U.S. patent application number 12/807555 was filed with the patent office on 2011-01-06 for cryopreserved selected sperm cell sample.
This patent application is currently assigned to -XY, LLC. Invention is credited to John L. Schenk.
Application Number | 20110004052 12/807555 |
Document ID | / |
Family ID | 26863156 |
Filed Date | 2011-01-06 |
United States Patent
Application |
20110004052 |
Kind Code |
A1 |
Schenk; John L. |
January 6, 2011 |
Cryopreserved selected sperm cell sample
Abstract
The present invention provides a method of cryopreserving sperm
that have been selected for a specific characteristic. In a
preferred embodiment, the method is employed to freeze sex-selected
sperm. Although the cryopreservation method of the invention can be
used to freeze sperm selected by any number of selection methods,
selection using flow cytometry is preferred. The present invention
also provides a frozen sperm sample that has been selected for a
particular characteristic, such as sex-type. In preferred
embodiments, the frozen sperm sample includes mammalian sperm, such
as, for example, human, bovine, equine, porcine, ovine, elk, or
bison sperm. The frozen selected sperm sample can be used in a
variety of applications. In particular, the sample can be thawed
and used for fertilization. Accordingly, the invention also
includes a method of using the frozen selected sperm sample for
artificial insemination or in vitro fertilization.
Inventors: |
Schenk; John L.; (Fort
Collins, CO) |
Correspondence
Address: |
CR MILES P.C.
405 Mason Court, Suite 119
Fort Collins
CO
80524
US
|
Assignee: |
-XY, LLC
|
Family ID: |
26863156 |
Appl. No.: |
12/807555 |
Filed: |
September 7, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11608079 |
Dec 7, 2006 |
7820425 |
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12807555 |
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10266562 |
Oct 7, 2002 |
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11608079 |
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09577246 |
May 24, 2000 |
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10266562 |
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09478299 |
Jan 5, 2000 |
7208265 |
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09577246 |
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60167423 |
Nov 24, 1999 |
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Current U.S.
Class: |
600/35 ;
435/325 |
Current CPC
Class: |
A01N 1/021 20130101;
A01N 1/0215 20130101; A01N 1/02 20130101; A01N 1/0221 20130101;
A01N 1/0226 20130101 |
Class at
Publication: |
600/35 ;
435/325 |
International
Class: |
A61B 17/43 20060101
A61B017/43; C12N 5/076 20100101 C12N005/076; A61D 19/02 20060101
A61D019/02 |
Claims
1. A frozen selected sperm sample comprising a portion of the sperm
present in a source sample, said portion of sperm selected for a
characteristic.
2. The frozen selected sperm sample of claim 1, wherein said frozen
selected sperm sample comprises sex-selected sperm.
3. The frozen selected sperm sample of claim 1, wherein said frozen
selected sperm sample comprises mammalian sperm.
4. The frozen selected sperm sample of claim 1, wherein said frozen
selected sperm sample is produced by a method comprising: (a)
obtaining a selected sperm sample, said selected sperm sample
containing a sufficient number of selected sperm cells to fertilize
an egg of a non-human mammal; and (b) freezing said selected
sperm.
5. The frozen selected sperm sample of claim 4, wherein said frozen
selected sperm sample is produced by the method further comprising
the step of adding an extender to said selected sperm sample.
6. The frozen selected sperm sample of claim 5, wherein said
extender comprises a final extender added to said selected sperm
sample prior to said freezing step, said final extender including
at least one cryoprotectant.
7. The frozen selected sperm sample of claim 4, wherein said frozen
selected sperm sample is produced by the method further comprising
the step of isolating selected sperm from said selected sperm
sample to produce isolated sperm.
8. The frozen selected sperm sample of claim 7, wherein said
extender comprises an initial extender added to said selected sperm
sample.
9. The frozen selected sperm sample of claim 8, wherein said
initial extender includes a component that maintains osmolality and
buffers pH.
10. The frozen selected sperm sample of claim 9, wherein said
initial extender further includes an organic substance that reduces
cold shock and preserves fertility of sperm.
11. The frozen selected sperm sample of claim 9, wherein said
initial extender further includes an energy source.
12. The frozen selected sperm sample of claim 9, wherein said
initial extender further includes an antibiotic.
13. The frozen selected sperm sample of claim 9, wherein a flow
cytometer selects said sperm, and wherein a sheath fluid flowed in
said flow cytometer comprises said initial extender.
14. The frozen selected sperm sample of claim 8, wherein said
initial extender further includes at least one cryoprotectant, said
initial extender including said at least one cryoprotectant added
after the step of isolating selected sperm as a final extender.
15. The frozen selected sperm sample of claim 14, wherein said
frozen selected sperm sample is produced by the method further
comprising the step of cooling said selected sperm sample.
16. The frozen selected sperm sample of claim 15, wherein said
frozen selected sperm sample is produced by the method further
comprising the step of cooling said selected sperm sample between
about 4.degree. Celsius and about 5.degree. Celsius.
17. The frozen selected sperm sample of claim 16, wherein said
frozen selected sperm sample is produced by the method further
comprising the step of cooling over a period of about 60 minutes to
about 240 minutes.
18. A method comprising using the frozen selected sperm sample of
claim 1 for artificial insemination.
19. A method comprising using the frozen selected sperm sample of
claim 1 for in vitro fertilization.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 10/266,562, filed Oct. 7, 2002, which is a
continuation of U.S. patent application Ser. No. 09/577,246, filed
May 24, 2000, which is a divisional of U.S. patent application Ser.
No. 09/478,299 filed Jan. 5, 2000 which claims the benefit of U.S.
Provisional Application No. 60/167,423, filed Nov. 24, 1999, each
hereby incorporated by reference herein.
FIELD OF THE INVENTION
[0002] The invention relates to a method for freezing sperm
selected for a particular characteristic, as well as to a frozen
selected sperm sample and methods of using such a sample. The
invention is particularly useful for preserving sex-selected
sperm.
BACKGROUND OF THE INVENTION
[0003] Over half a century ago, artificial insemination was
introduced in the United States as a commercial breeding tool for a
variety of mammalian species. Although artificial insemination was
initially limited to regions relatively close to the site of sperm
collection, advances in the cryopreservation and storage of sperm
have facilitated widespread distribution and commercialization of
sperm intended for artificial insemination or in vitro
fertilization.
[0004] Further improvements in mammalian sperm collection,
selection, cryopreservation, storage, and handling techniques have
enhanced the ability of breeders to produce animals having desired
traits. For example, advances in selection of mammalian sperm based
on slight differences in physical characteristics has made it
possible to separate sperm based on sex-type, that is, to select
for cells containing either the X or Y chromosome. This technique
allows the breeder to manipulate the relative percentage of X- or
Y-type sperm in a sample and thereby determine offspring sex. The
ability to select sperm based on sex-type or any other desirable
characteristic provides an important tool for accelerating genetic
progress, increasing production efficiency, and achieving greater
flexibility in livestock management. Full exploitation of this
tool, however, depends on the ability to freeze and store selected
sperm.
[0005] A variety of methods are available for selecting cells;
however, the selection and subsequent processing of sperm presents
unique challenges because sperm are incapable of DNA repair and
because of sperm morphology. Each sperm has an acrosome overlying
the head and a tail, which are important for fertility and which
are relatively susceptible to physical injury. In addition, sperm
fertility decreases with increasing time between collection and
use. As most of the available selection methods involve physical
stresses and take time, selected sperm are typically somewhat
compromised compared to non-selected cells. Fertility may be
further reduced if the selection technique involves significant
dilution. It has been suggested that this "dilution effect" may be
due to the loss of protective components in seminal plasma.
[0006] Flow cytometry is a particularly efficient selection method
that has been employed for sorting sperm by sex-type. However,
sorted sperm are subject to stresses beyond those normally
encountered in standard artificial insemination or in vitro
fertilization protocols. In particular, flow cytometry is time
consuming, and, because of the physical constraints of flow
cytometers, sperm must be diluted for sorting to levels that are
not optimal for storage. (usually to on the order of
10.sup.5-10.sup.6/ml). Furthermore, sorted sperm intended for
artificial insemination must be concentrated so that conventional
packaging and delivery equipment can be used. The need for a
concentration step thus exposes already somewhat compromised sperm
to additional physical stresses.
[0007] The freezing of sperm also invariably reduces fertility,
motility, and/or viability, and, although techniques for freezing
unselected sperm are well known, no technique for cryopreservation
of selected sperm has been described.
SUMMARY OF THE INVENTION
[0008] The present invention provides a method of cryopreserving
sperm that have been selected for a specific characteristic. The
method is particularly useful for cryopreserving sperm selected by
a method that results in dilution of the sperm, since the method
provides for the isolation of sperm from a selected sperm sample,
followed by addition of a final extender to the isolated sperm to
produce a suspension having a desired concentration of sperm. In a
preferred embodiment, the method is employed to freeze sex-selected
sperm. Although the cryopreservation method of the invention can be
used to freeze sperm selected by any number of selection methods,
selection using flow cytometry is preferred.
[0009] The present invention also provides a frozen sperm sample
that has been selected for a particular characteristic, such as
sex-type. In preferred embodiments, the frozen sperm sample
includes mammalian sperm, such as, for example, human, bovine,
equine, porcine, ovine, elk, or bison sperm. Also within the scope
of the invention is a container including a frozen sperm sample
according to the invention.
[0010] The frozen selected sperm sample can be used in a variety of
applications. In particular, the sample can be thawed and used for
fertilization. Accordingly, the invention also includes a method of
using the frozen selected sperm sample for artificial insemination
or in vitro fertilization.
DETAILED DESCRIPTION OF THE INVENTION
[0011] The present invention allows cryopreservation of sperm that
have been selected for a particular characteristic, facilitating
storage and/or shipment of selected sperm samples to sites distant
from the collection site. Thawing yields viable sperm that can be
used in procedures such as artificial insemination ("AI") and in
vitro fertilization ("IVF"). This result was surprising because of
the well-documented fragility of sperm. Prior researchers had
demonstrated that the stresses associated with various selection
methods or with cryopreservation resulted in significant losses in
fertility and/or viability. The present inventors have
demonstrated, for the first time, that pregnancies can be achieved
with sperm that have been selected and then frozen.
[0012] The invention represents an important advance in livestock
management, where selection of sperm for use in such procedures can
be used to increase the production of offspring having desirable
traits. For example, selection to obtain sperm carrying either the
X or the Y chromosome allows control over offspring sex, which is
advantageous for producers of animals such as dairy or beef cattle.
Sex selection also finds application in breeding valuable (e.g.,
show or race horses) or endangered animals. The ability to freeze
selected sperm, which the invention provides, will enable
widespread use of such selection methods to, e.g., increase
livestock production efficiency as well as quality.
DEFINITIONS
[0013] The term "acrosome" or "acrosomal cap" refers to the cap
that covers the anterior half of the head of sperm and that
contains enzymes necessary for ovum penetration.
[0014] The term "sex-type" refers to the type of sex chromosome
present in the sperm (i.e., the X or Y chromosome).
[0015] The term "capacitation" refers to the specific changes a
sperm undergoes to develop the capacity to fertilize ova, such as
enzymic changes on the surface of the acrosome that lead to release
of acrosomal enzymes that facilitate penetration of the sperm into
the ovum.
[0016] As used with reference to sperm, the term "cryoprotectant"
refers to a molecule that protects sperm during a freeze-thaw
cycle, promoting survival and retention of fertilizing
capacity.
[0017] The term "dilution effect" refers to the rapid decline in
motility and/or viability of sperm when highly diluted.
[0018] As used herein, the term "selection" refers to a method
whereby a sample is subdivided based on presence or absence of a
specific characteristic (unless context dictates otherwise). Thus,
a "selected sperm sample" is a sample obtained by subjecting a
source sample to selection for the specific characteristic. A
selected sperm sample is therefore enriched, relative to the source
sample, in sperm having the specific characteristic.
[0019] The term "sorting" is used herein to describe a selection
method carried out using a fluorescence-activated cell sorter
(FACS).
[0020] The term "extender" refers to any medium that tends to
preserve sperm viability. The term "extension" refers to the
dilution of sperm with extender.
[0021] The term "initial extender" refers to a medium used to
extend sperm prior to the isolation step of the method of this
invention.
[0022] The term "final extender" refers to a medium used to extend
sperm prior to the freezing step of the method of this
invention.
[0023] An "organic substance" in an extender described herein is
any organic substance that tends to reduce cold shock and preserve
fertility of sperm.
[0024] An "energy source" in an extender described herein is any
substance or substrate that sperm can utilize for cell maintenance
and/or motility.
[0025] The term "osmolality," as used herein, is a measure of the
osmotic pressure of dissolved solute particles in a an aqueous
solution (e.g., an extender). The solute particles include both
ions and non-ionized molecules. Osmolality is expressed as the
concentration of osmotically active particles (i.e., osmoles)
dissolved in 1 kg of water.
Cryopreservation Method
[0026] The invention provides a method of cryopreserving selected
sperm includes the following steps:
[0027] (1) obtaining a selected sperm sample;
[0028] (2) cooling the selected sperm sample;
[0029] (3) isolating sperm from the selected sperm sample;
[0030] (4) adding final extender to the isolated sperm to produce a
suspension of sperm; and
[0031] (5) freezing the suspension of sperm.
Obtaining a Selected Sperm Sample
[0032] The first step in the cryopreservation method of the
invention encompasses obtaining a previously selected sperm sample,
as well as subjecting a source sample to any suitable selection
method. Sperm from any species can be selected and frozen according
to the method of the invention. The method can be carried out with
sperm from domesticated animals, especially livestock, as well as
with sperm from wild animals (e.g., endangered species).
Preferably, the selected sperm sample contains mammalian sperm.
Human sperm, bovine, equine, porcine, ovine, elk, and bison sperm
are particularly preferred.
[0033] Generally, the selected sperm sample contains normal, viable
sperm. To this end, the ejaculate from which the sperm are obtained
typically has at least about 50%, and preferably at least about 75%
morphologically normal sperm. In these embodiments, generally at
least about 40%, and preferably at least about 60% of the sperm in
the ejaculate exhibit progressive motility.
[0034] A wide variety of methods for selecting cells from a mixed
populations are available, including, for example, selection based
on binding of cells or cell components with antibodies, antibody
fragments, or other binding partners and differential staining.
[0035] The invention is exemplified herein with selection based on
sex-type, and sex-selected sperm for use in the invention can be
obtained using any selection strategy that takes advantage of
slight differences in characteristics between X- and Y-type sperm.
Exemplary sex-selection methods include magnetic techniques (see,
e.g., U.S. Pat. No. 4,276,139), columnar techniques (see, e.g.,
U.S. Pat. No. 5,514,537) gravimetric techniques (see, e.g., U.S.
Pat. No. 3,894,529, reissue Pat. No. 32350, U.S. Pat. Nos.
4,092,229, 4,067,965, and 4,155,831). Sex-selection based on
differences in electrical properties is disclosed in U.S. Pat. No.
4,083,957, and techniques that select based on differences in
electrical and gravimetric properties are discussed in U.S. Pat.
Nos. 4,225,405, 4,698,142, and 4,749,458. U.S. Pat. Nos. 4,009,260
and 4,339,434 describe selection based on differences in motility.
Biochemical techniques relying on antibodies are disclosed in U.S.
Pat. Nos. 4,511,661, 4,999,283, 3,687,806, 4,191,749, 4,448,767,
whereas U.S. Pat. Nos. 5,021,244, 5,346,990, 5,439,362, and
5,660,997 describe selection based on differences in membrane
proteins.
[0036] Flow cytometry is a preferred method for separating cells
from mixed populations based on differential staining with
fluorescent dyes or binding to fluorescently labeled molecules,
such as antibodies or nucleic acids. In fluorescence activated cell
sorting ("FACS"), cells are "sorted" into different populations
based on the fluorescence intensity upon irradiation. FACS can be
used for sex-selection of sperm because the X chromosome contains
slightly more DNA than the Y chromosome. When sperm are stained
with a fluorescent DNA-binding dye, X-chromosome bearing sperm
absorb more dye than Y chromosome bearing sperm and the two
populations can therefore can be separated by FACS. This strategy
was discussed in U.S. Pat. No. 4,362,246 and significantly expanded
upon in U.S. Pat. No. 5,135,759 (issued to Johnson). Separation has
been enhanced through-the use of high-speed flow cytometers, such
as the MoFlo.RTM. flow cytometer produced by Cytomation, Inc. (Ft.
Collins, Colo.) and described in U.S. Pat. Nos. 5,150,313,
5,602,039, 5,602,349, and 5,643,796, as well as in PCT Publication
No. WO 96/12171.
[0037] The selection method used to obtain the selected sperm
sample is preferably one that preserves sperm viability. Because of
the relative fragility of sperm, normal flow cytometry techniques
should generally be modified for sorting sperm. More specifically,
the flow cytometry entails staining, dilution, and interrogation of
cells with light. All of these steps represent stresses that can
reduce sperm viability. The sensitivity of sperm to these stresses
can vary between species and even between individuals within
species. Such sensitivities have either been documented or can
readily be determined by empirical studies, such as those described
in Examples 1-5.
[0038] Modifications that enhance viability are described the
patent publications discussed above. For instance, procedures that
provide improved sheath and collector systems for sorting sperm are
disclosed in PCT Publication No. WO 99/33956 (Application No.
PCT/US98/27909). Further, Examples 1-7 below describe exemplary
procedures for staining and sorting sperm. Example 3 describes a
study of the effects of laser intensity and dye concentration of
post-thaw motility of sorted frozen sperm. This study indicates
that the use of lower laser intensities during sorting can increase
post-thaw motility.
[0039] The selected sperm sample can contain a variety of
components besides sperm and will often contain components added to
protect the sperm during the selection process. In the case of
FACS, the selected sperm sample can contain component(s) of the
solutions used for staining and sorting (e.g., the sheath fluid and
the catch buffer).
[0040] In addition, the selected sperm sample typically contains an
extender or extender fraction. For example, "two-step" extenders
including an "A fraction" lacking glycerol and a "B fraction"
containing glycerol are well known. The A fraction is added to
sperm first, followed by addition of an equal volume of the B
fraction. For this step, the B fraction is often divided into at
least two aliquots and added sequentially; e.g., the second B
fraction aliquot is added 15 minutes after the first.
[0041] If no extender components are present, an extender or
extender fraction is typically added to the selected sperm sample
before the sperm are isolated from the sample. If only some
extender components are present, additional components can
optionally be added so that selected sperm sample includes a
complete extender or an extender fraction before the isolation
step. In exemplary embodiments, bovine sperm are flow-sorted so as
to produce a selected sperm sample including the A fraction of an
extender (see Examples 2, 3, and 4). If desired, the B fraction can
then be added to the selected sperm sample before the isolation
step (see Example 5). The pre-isolation step extender (or extender
fraction) is termed "the initial extender" to distinguish it from
the "final extender" employed for the extension of isolated sperm
before freezing. If the selected sperm sample was selected using
FACS, the initial extender can be matched to the sheath fluid
employed for sorting. Exemplary matched sheath fluids and extenders
are described in detail in Example 4.
[0042] An extender suitable for use in the selected sperm sample
includes a physiologically acceptable carrier. The physiologically
acceptable carrier is typically aqueous, and, in preferred
embodiments, includes deionized water. Suitable extenders commonly
comprise one or more of the following additional components: a
cryoprotectant, a component that maintains osmolality and buffers
pH, an organic substance that prevents cold shock and preserves
fertility of sperm, a detergent that acts synergistically with
certain organic substances to enhance preservation of sperm, an
energy source that can be readily utilized by sperm, an
antioxidant, which protects sperm from cold shock, a substance that
facilitates sperm capacitation, and one or more antibiotics.
[0043] Although cryoprotectants useful in the invention are not
limited to those acting by a particular mechanism, most
conventional cryoprotectants act, at least in part, by reducing
intracellular dehydration. Specifically, freezing is accompanied by
an increase in solute concentration in the medium surrounding
sperm. This increase in solute concentration draws water out of the
cells, which increases intracellular electrolyte concentration.
Exemplary cryoprotectants include glycerol, dimethyl sulfoxide,
ethylene glycol, propylene glycol, and the like. The cryoprotectant
suitable for use in a given extender can vary, depending on the
species from which sperm are derived. For example, glycerol is
suitable for use in cryopreservation of human and bovine sperm, but
is generally not used for cryopreservation of porcine or rabbit
sperm. Such preferences are well known for many commercially
valuable sperm and can readily be determined empirically for other
types of sperm.
[0044] The extender useful in the invention optionally includes one
or more components that help maintain osmolality and provide
buffering capacity. In preferred embodiments of the invention, the
osmolality of the extender approximates that of physiological
fluids. More preferably, the osmolality of the extender is in the
range of about 280 mOsm to about 320 mOsm. The pH is also
preferably within a physiologically acceptable range, more
preferably in the range of about 6.5 to about 7.5.
[0045] Substances helpful in maintaining osmolality and pH within
these ranges are well known in the art and can be added to the
extender as a solid or already in solution. A buffer containing a
salt, a carbohydrate, or a combination thereof can be employed for
this purpose. Specific examples include sodium citrate,
Tris[hydroxymethyl]aminomethane, and TES (N-Tris
[Hydroxymethyl]methyl-2-aminoethanesulfonic acid), and monosodium
glutamate buffers; milk; HEPES-buffered medium; and any combination
thereof. The component employed to help maintain osmolality and
provide buffering capacity in a particular application can vary
depending on the other components of the extender and, in some
cases, on the species from which the sperm are derived. The
selection of such a component for use in the present invention is,
however, within the level of skill in the art.
[0046] One or more organic substances that protect sperm against
cold shock and help preserve fertilizing capacity can also be
included in the extender. Such substances are well known and are
sometimes described as "nonpenetrating cryoprotectants." One
skilled in the art can readily determine an organic substance
suitable for a particular application of the cryopreservation
method described herein. For example, organic substances containing
protective constituents (e.g., lipoproteins, phospholipids,
lecithin) that are believed to reduce the impact of cold shock and
the dilution effect can be included in the extender. Suitable
organic substances include disaccharides, trisaccharides, and any
combination thereof. Exemplary organic substances include egg yolk,
an egg yolk extract, milk, a milk extract, casein, albumin,
lecithin, cholesterol, and any combination thereof.
[0047] The extender can also include a detergent. Alkyl ionic
detergents, such as sodium dodecyl sulfate (SDS), have been
reported to act synergistically with egg yolk to enhance protection
against cold shock. Other detergents useful in the cryopreservation
of cells can also be employed in the extender, and the selection of
a particular detergent for a specific application is within the
level of skill in the art in light of the guidance provided herein.
See, e.g., Example 5.
[0048] Preferably, the extender includes an energy source that is
readily utilized by sperm. In the absence of an energy source,
sperm may oxidize intracellular phospholipids and -other cellular
components. Thus, the inclusion of an energy source in the extender
protects intracellular reserves and cellular components. As is well
known in the art, sugars, particularly monosaccharides, provide a
convenient energy source, although any conventional energy source
can be employed in the extender. Exemplary monosaccharides useful
in the extender include glucose, fructose, and/or mannose.
[0049] One or more antioxidants can optionally be included in the
extender to provide additional protection against cold shock.
Exemplary antioxidants include butylated hydroxytoluene (BHT), its
derivatives, and the like. However, other antioxidants useful in
the cryopreservation of cells can also be employed in the extender,
and the selection of a particular antioxidant for a specific
application is within the level of skill in the art in light of the
guidance provided herein.
[0050] The extender can also contain a substance that facilitates
sperm capacitation. A variety of capacitation facilitators are
known in the art and any can be employed in the extender. Examples
include enzymes such as alpha amylase, beta amylase, beta
glucuronidase, which can be used in combination, if desired.
[0051] Finally, the extender preferably includes an antibiotic,
since substantial bacterial growth can threaten sperm viability and
increase the risk of infection of the host in artificial
insemination or in vitro fertilization procedures. Any of a variety
of antibiotics useful in the cryopreservation of cells can also be
employed in the extender. The selection of a suitable antibiotic
depends on the species from which the sperm was obtained, the
procedures involved in obtaining and handling the sperm sample, and
the specific microorganism(s) to be targeted. Exemplary antibiotics
include tylosin, gentamicin, lincomycin, spectinomycin,
linco-spectin (a combination of lincomycin and spectinomycin),
penicillin, streptomycin, and ticarcillin, which can be used alone
or in combination. However, one skilled in the art can readily
determine other antibiotics suitable for use in the extender.
[0052] Exemplary extenders are discussed in greater detail below
and in the examples.
[0053] The sperm concentration is typically lower in the selected
sperm sample than in the source sample, and, as indicated above,
when FACS is employed, the dilution is significant. A typical sort
based on sex-type can produce a sample containing sperm at
6.times.10.sup.5 cells/ml catch buffer. As such a low concentration
is not optimal for storage (at least for most species tested), the
cryopreservation method of the invention generally concentrates the
selected sperm sample.
Cooling the Selected Sperm Sample
[0054] The second step in the cryopreservation method entails
cooling the selected sperm sample, typically, by reducing the
temperature at a controlled rate. Cooling too rapidly can cause
cold shock, which can result in a loss of membrane integrity and
cell function. The severity of the effects of cold shock vary from
species to species and depend on factors such as the rate of
cooling and the temperature range. Under suitable controlled
cooling conditions, the sperm are able to adapt to thermal effects.
Example 2, among others, describes conditions for cooling bovine
sperm, and determining suitable conditions for cooling sperm of
other species is within the level of skill in the art.
[0055] In a preferred embodiment of the invention, the selected
sperm sample is cooled typically from about 22.degree. Celsius, to
about 5.degree. Celsius, and cooling is generally carried out over
a period of about 60 minutes to about 24 hours, preferably over a
period of about 90 minutes to about 240 minutes, and most
preferably over a period of about 90 minutes to about 120 minutes.
Cooling can be accomplished by any convenient method, including
simply placing the selected sperm sample in a 5.degree. Celsius
environment.
Isolation of Sperm Cells from the Selected Sperm Sample
[0056] After initial extension of the selected sperm sample, sperm
are isolated from the sample using any sufficiently gentle
isolation method that provides at least about 50% recovery of
sperm, more preferably about 75% to about 90% recovery of sperm,
and most preferably about 80% to about 90% recovery of sperm.
During the isolation step, the cooled sperm should generally be
kept cold, i.e., between about 1 and about 8.degree. Celsius, and
preferably close to 4 or 5.degree. Celsius.
[0057] Any of a variety of methods suitable for recovering cells
from a suspension can be used to isolate the sperm, including for
example, filtration, sedimentation, and centrifugation. In an
exemplary, preferred embodiment, the selected sperm sample is
aliquoted into 50 ml tubes at volumes not exceeding about 27 ml,
and preferably between about 20 to about 27 ml. Centrifugation is
carried out at about 4.degree. Celsius, at about 850.times.g, for
about 20 minutes. Preferably, the centrifugation step provides at
least about 50% to about 90% recovery of sperm, more preferably
about 60% to about 90% recovery of sperm, and most preferably about
70% to about 90% recovery of sperm. After isolation, the
supernatant is removed and the pellet is suspended by vortexing
gently or repeated aspiration at 4.degree. Celsius. The sperm
concentration is then typically determined (e.g., using a
hemacytometer).
Final Extension of Isolated Sperm Cells
[0058] After isolation, the sperm are pooled, if desired, and
extended with final extender to an appropriate concentration for
freezing. The concentration of sperm after the final extension and
prior to freezing is preferably in the range of about
1.times.10.sup.6/ml to about 300.times.10.sup.6/ml, more preferably
about 10.times.10.sup.6/ml to about 50.times.10.sup.6/ml, and most
preferably about 10.times.10.sup.6/ml to about
20.times.10.sup.6/ml.
[0059] The description of the initial extender above also applies
to the final extender, which can be the same as or different from
the initial extender. In particular embodiments, the composition of
the sperm sample extended with the final extender is substantially
similar to (if not the same as) the composition of the sperm sample
after addition of the initial extender.
[0060] In a preferred embodiment of the invention, an egg yolk-Tris
extender is used. After the addition of the extender, the sperm
suspension comprises glycerol (cryoprotectant); citric acid and
Tris[hydroxymethyl]aminomethane (buffer); egg yolk (organic
substance); fructose (energy source); tylosin, gentamicin, and
linco-spectin (antibiotics). The typical approximate concentrations
of these components after addition of the final extender to the
isolated sperm are:
Components of Egg Yolk-Tris Extender
[0061] Glycerol: 4-8% vo/vol [0062] Citric Acid: 55-75 mM [0063]
Tris [hydroxymethyl]aminomethane: 190-210 mM [0064] Egg yolk: 5-25%
vol/vol [0065] Fructose: 45-65 mM [0066] Tylosin: 25-100 .mu.g/ml
[0067] Gentamicin: 200-300 .mu.g/ml [0068] Linco-spectin: 100-400
.mu./ml* *100-400 .mu.g/ml lincomycin and 100-400 .mu.g/ml
spectinomycin
[0069] In a variation of this embodiment particularly suitable for
freezing bovine sperm, the concentrations of these components after
addition of the final extender to the isolated sperm are about 6%
(vol/vol) glycerol, about 65 mM citric acid, about 200 mM
Tris[hydroxymethyl]aminomethane, about 20% (vol/vol) egg yolk,
about 56 mM fructose, about 50 .mu.g/ml tylosin, about 250 .mu.g/ml
gentamicin, and about 150/300 .mu.g/ml linco-spectin (i.e., 150
.mu.g/ml lincomycin and 300 .mu.g/ml spectinomycin), in deionized
water.
[0070] In an alternative embodiment, an egg yolk-citrate extender
is employed. After the addition of the extender, the sperm
suspension comprises glycerol (cryoprotectant); sodium citrate
(buffer); egg yolk (organic substance); tylosin, gentamicin, and
lino-spectin (antibiotics). The typical approximate concentrations
of these components after addition of the final extender to the
isolated sperm are:
Components of Egg Yolk-Citrate Extender
[0071] Glycerol: 4-8% vol/vol [0072] Sodium Citrate: 60-80 mM
[0073] Egg yolk: 5-25% vol/vol [0074] Tylosin: 25-100 .mu.g/ml
[0075] Gentamicin: 200-300 .mu.g/ml [0076] Linco-spectin: 100-400
.mu.g/mL* *100-400 .mu.g/ml lincomycin and 100-400 .mu.g/ml
spectinomycin
[0077] Exemplary, preferred concentrations for freezing bovine
sperm are about 7% (vol/vol) glycerol, about 72 mM sodium citrate,
about 20% (voUvol) egg yolk, about 50 .mu.g/ml tylosin, about 250
.mu.g/ml gentamicin, and about 250/300 .mu.g/ml linco-spectin.
[0078] In another alternative embodiment, an egg yolk-TES-Tris ("EY
TEST") extender is employed. After the addition of the extender,
the sperm suspension comprises glycerol (cryoprotectant); egg yolk
and heated milk, e.g., homogenized milk containing 1.25% fructose
with 10% glycerol (organic substances); tylosin, gentamicin, and
linco-spectin (antibiotics). The typical approximate concentrations
of these components after addition of the final extender to the
isolated sperm are:
Components of Egg Yolk TES-Tris Extender
[0079] Glycerol: 3-7% vol/vol Tris
[hydroxymethy-methyl]-2-aminoethanesulfonic acid: 140-170 mM Tris
[hydroxymethyl]aminomethane; 60-80 mM Egg yolk: 5-25% voUvol
Fructose: 5-12 mM
Tylosin: 50-150 .mu./ml
[0080] Gentamicin: 400-600 .mu.g/ml Linco-spectin: 200-700
.mu.g/mL* *200-700 .mu.g/mllincomycin and 200-700 .mu.g/ml
spectinomycin
[0081] Exemplary, preferred concentrations for freezing bovine
sperm are about 5% (vol/vol) glycerol, about 158 mM
Tris[hydroxymethy-methyl]-2-aminoethanesulfonic acid, about 72 mM
Tris[hydroxymethyl]aminomethane, about 20% (vol/vol) egg yolk,
about 8 mM fructose, about 100 .mu.g/mL tylosin, about 500 .mu.g/ml
gentamicin, and about 300/600 .mu.g/ml linco-spectin.
[0082] In yet another alternative embodiment of the invention, a
Milk extender is employed. After the addition of the extender, the
sperm suspension comprises glycerol (cryoprotectant); heated
homogenized milk (organic substance); fructose (energy source); and
tylosin, gentamicin, and linco-spectin (antibiotics). The typical
approximate concentrations of these components after addition of
the final extender to the isolated sperm are:
Components of Milk Extender
Homogenized Milk 90% (Vol/Vol)
[0083] Glycerol: 3-7% (vol/vol) Fructose: 1.25% (wt/vol) Tylosin:
50 .mu.g/ml Gentamicin: 250 .mu.g/ml Linco-spectin: 250/300
.mu.g/ml* *250-300 .mu.g/ml lincomycin and 250-300 .mu.g/ml
spectinomycin
[0084] Exemplary preferred concentrations for freezing bovine sperm
are about 90% milk, about 10% (vol/vol) glycerol, about 1.25%
fructose (wt/vol?), about 50 .mu.g/ml tylosin, about 250 .mu.g/ml
gentamicin, and about 250/300 .mu.g/ml linco-spectin.
[0085] Other extenders standardly used to freeze sperm can also be
employed as the final extender in freezing selected sperm. A
variety of extenders optimized for use in freezing sperm from
various species have been described, and many are commercially
available. Freezing extenders for equine sperm typically consist of
milk, egg yolk, various sugars, electrolytes and a cryoprotectant.
Exemplary freezing extenders are described by Squires, E. L., et
al., Cooled and Frozen Stallion Semen Animal Reprod. and
Biotechnology Laboratory, Bulletin No. 69, Chapter 8, "Seminal
Extenders" pp. 49-51 (July, 1999).
Equilibration and Freezing of Sperm
[0086] Extension of the sperm sample produces a suspension of
sperm, which is then transferred into containers for freezing. If
the sperm are intended for use in fertilization, the cells are
conveniently aliquoted into individual doses sufficient to achieve
fertilization. The required dose can vary substantially from one
species to the next and is either well-known (e.g., for cattle and
horses) or can readily be determined. In the case of sex-selected
bovine sperm, convenient doses range from about 1.0.times.10.sup.6
sperm to about 3.0.times.10.sup.6 sperm.
[0087] Any suitable container can be employed for freezing,
including, for example, an ampule, a vial, and a straw. Sperm
intended for AI are typically frozen in straws (e.g., 0.25 ml or
0.50 ml straws) designed for use with an insemination gun.
Preferably, a bolus of extender is drawn into the straw, followed,
in sequence, by air, sperm, air, and extender, so that the sperm
are flanked on either side by an air space, which separates the
sperm from a bolus of extender at either end of the straw.
[0088] Prior to freezing, the sperm are generally allowed to
equilibrate at about 5.degree. C. Preferably, the sperm are allowed
to equilibrate for a period in the range of about 1 hour to about
18 hours, more preferably between about 3 hours and about 18 hours,
and most preferably between about 3 hours and about 6 hours (see
Example 2). Following equilibration, any standard freezing method
can be employed, provided the freezing rate is not too rapid (i.e.,
not in excess of about 0.5.degree. C./minute). Preferably, the
freezing rate is about 0.5.degree. C./minute. In an exemplary,
preferred embodiment, the sperm are placed in static liquid
nitrogen vapor, and freezing is carried out in three distinct
stages over a period of about 10 minutes. In the first stage of
freezing, the sperm are cooled from about 5.degree. C. to about
-15.degree. C. at a rate of about 40.degree. C./minute to about
65.degree. C./minute. In the second stage of freezing, the sperm
are cooled from about -15.degree. C. to about -60.degree. C. at a
rate of about 25.degree. C./minute to about 35.degree. C./minute.
In the third stage, the sperm are plunged into liquid nitrogen at
about -100.degree. C.
Selected Sperm Samples
[0089] In addition to a freezing method, the invention provides a
frozen sperm sample including sperm selected from a source sample
for a particular characteristic. The sperm can be from any species,
including any of those discussed above with reference to the
freezing method. The invention encompasses frozen sperm selected
for any characteristic by any suitable method, such as those
described above. Preferred embodiments include frozen sex-selected
human, bovine, equine, porcine, ovine, elk, or bison sperm.
Sex-selection is preferably carried out using flow cytometry as
described generally above.
[0090] Also within the scope of the invention is a container
containing a frozen sperm sample according to the invention. The
container can be formed from any material that does not react with
the frozen sperm sample and can have any shape or other feature
that facilitates use of the sample for the intended application.
For samples intended for use in AI, for example, the container is
conveniently a straw (e.g., 0.25 ml or 0.5 ml straw) designed for
use with an insemination gun. The container is sealed in any manner
suitable for preserving the sample at the intended storage
temperature, which is typically below -80.degree. Celsius. 0.25 ml
straws can be sealed, for instance, with PVC powder,
ultrasonically, or with a cotton-polyvinyl plug and/or a stainless
steel ball (BB).
[0091] As the frozen sperm sample of the invention is typically
thawed before use, the invention also provides a thawed, previously
frozen, selected sperm sample and a container including such a
thawed sample.
Methods of Using the Selected Sperm Sample
[0092] The frozen selected sperm sample of the invention is
suitable for use in any method in which sperm are used. The sample
can be thawed and used in any conventional fertilization method,
such as artificial insemination or in vitro fertilization. Thawing
is carried out in the same manner as for frozen, non-selected
sperm. Briefly, the straw containing the frozen sperm is submerged
in a water bath maintained at a temperature of about 35.degree. C.
to about 37.degree. C. for a period of about 20 to about 30
seconds. After thawing, semen deposition (e.g., insemination) is
carried out according to standard procedures, taking care to
protect the sperm from environmental fluctuations.
EXAMPLES
Example 1
Effects of Dilution on Sperm
[0093] Objective: to determine the effect of sperm concentration on
sperm motility for non-frozen, non-sorted, but highly diluted
sperm.
A. EFFECTS OF DILUTION ON NON-WASHED SPERM
[0094] 1. Collection of Source Sample. Sperm were collected from
bulls on a routine collection schedule using an artificial vagina
as described in Schenk J., Proc 17th NAAB, p. 48-58 (1998), and
Saacke R G, Proc NAAB Tech Conf A1 Reprod. 41:22-27 (1972). All
ejaculates used contained greater than 50% progressively motile and
greater than 75% morphologically normal sperm. Antibiotics were
added to the raw ejaculate as described by Shin S., Proc NAAB Tech
Conf AI Reprod. 11:33-38 (1986) within 15 minutes of collection,
and the concentration of sperm was determined using a
spectrophotometer.
[0095] 2. Methods. Sperm from 4 bulls were diluted to 1.25, 2.5, 5,
10, 15, and 20.times.10.sup.6/ml using an egg yolk-citrate extender
(EYC) prepared with 20% egg yolk (vol/vol) in 72 mM sodium citrate,
50 .mu.g/ml tylosin, 250 .mu.g/ml gentamicin, and 250/300 .mu.g/ml
linco-spectin. Each sample was prepared in duplicate (2
tubes/dilution/bull) and comprised 8 ml total volume per tube. All
samples were incubated for 60 minutes at 22.degree. C., after which
they were centrifuged using a swinging bucket centrifuge
(Eppendorf, Model # 5810R) at 600.times.g for 10 minutes to
concentrate the sperm. After centrifugation, the supernatant from
one set of the duplicate tubes was not removed; the sperm were
resuspended in the same medium and at the original concentration by
repeated gentle aspiration using a 5-ml serological pipette. (The
second set of the duplicate tubes were used in Example IB.) Sperm
samples were then cooled to 5.degree. C. at 0.2.degree. C./min over
90 minutes. These sperm were termed "non-washed sperm." All samples
were incubated at 5.degree. C. for 24 or 48 h post-collection.
[0096] 3. Evaluation of Motility. After incubation, the samples
were warmed to 37.degree. C. using a dry block incubator for 10
minutes prior to determination of motility. For this experiment, a
single, blind estimate of the percentage of progressively motile
sperm was determined for each sample. Progressive sperm motility
was determined subjectively for each subclass by a single observer
(.times.200, phase-contrast microscopy); another person prepared
the microscope slides in a randomized manner so the observer was
unaware of treatments.
[0097] 4. Statistical Analysis. Data were analyzed by analysis of
variance (SAS Institute, Cary, N.C.) with factors bulls and initial
dilution concentration. Separate analyses were done for each
incubation time. Dilution trends were tested using (log) linear
contrasts.
[0098] 5. Results. Data for non-washed sperm (Table 1) revealed
(log) linear relationships (P<0.01) for both incubation times.
Percentages of motile sperm increased as sperm concentration
increased from 1.25.times.10.sup.6/ml to 10.times.10.sup.6/ml, but
there was little difference thereafter. The cubic term was
significant (P<0.05) for 24-h and marginally significant
(P<0.1) for 48-h incubations. There was a bull effect
(P<0.01) at both times.
TABLE-US-00001 TABLE 1 Effects of cooling on non-washed sperm
motility (%) after cooling to 5.degree. C. Dilution Incubation at
5.degree. C. (10.sup.6/ml) 24 h.sup.a 48 h.sup.b 1.25 18.sup.c
0.sup.c 2.5 38.sup.c,d 6.sup.c,d 5.0 56.sup.d 31.sup.d,e 10.0
61.sup.d 42.sup.e 15.0 55.sup.d 44.sup.e 20.0 58.sup.d 41.sup.e
S.E.sup..f 5.6 6.4 .sup.a(log) linear (P < 0.01) and cubic
effects (P < 0.05). .sup.b(log) linear (P < 0.01) and cubic
effects (P < 0.1). .sup.c,d,eMeans within columns without common
superscripts differ (P < 0.05). .sup.f {square root over (error
mean square of ANOVA)} / {square root over (N)} (SAS Institute,
Cary, NC, USA)
B. EFFECTS OF DILUTION ON WASHED SPERM
[0099] 1. Collection of Source Sample. The second set of the
duplicate tubes containing samples prepared in Example 1A were used
in this experiment.
[0100] 2. Methods. The sperm were diluted, incubated and
concentrated by centrifugation as in Example IA. Following
centrifugation, 7.1 ml of the supernatant was aspirated from each
tube, removing most of the seminal plasma and leaving the sperm in
a 900-.mu.l pellet. The sperm were diluted with EYC (see Example
1A) to make 10.times.10.sup.6/ml or 20.times.10.sup.6/ml sperm
suspensions. The samples were then cooled to 5.degree. C. over 90
minutes as in Example 1A.
[0101] 3. Evaluation of Motility. The samples were warmed and
evaluated for progressive motility as in Example 1A.
[0102] 4. Statistical Analysis. Data were analyzed as in Example
1A. In addition, data in Example 1B were analyzed for incubation
concentration at 5.degree. C.
[0103] 5. Results. Data for washed sperm (Table 2) revealed no
significant treatment effects when sperm were evaluated after 24 h.
However, after storage for 48 h at 5.degree. C., there were bull,
initial dilution, incubation concentration and bull by incubation
effects (P<0.05). More sperm remained motile when held at
20.times.10.sup.6/ml than at 10.times.10.sup.6/ml (31% vs. 20%;
P<0.05). Initial dilutions of 1.25, 2.5, and 5.times.10.sup.6
sperm/ml resulted in lower progressive motility than
10.times.10.sup.6 sperm/ml (P<0.05), with respective main effect
means of 19, 20, 27, and 37% motile sperm.
TABLE-US-00002 TABLE 2 Cumulative effects of washing, dilution,
concentration and cooling on progressive sperm motility (%) Sperm
conc (10.sup.6/ml) Storage at 5.degree. C.--Sperm Concentration
during 1 h and Duration preincubation 24 h 48 h.sup.a at 37.degree.
C. 20 .times. 10.sup.6/m1 10 .times. 10.sup.6/ml 20 .times.
10.sup.6/ml 10 .times. 10.sup.6/ml.sup.b 1.25 45 49 24 15 2.5 51 40
29 11 5.0 54 54 32 21 10.0 51 50 40 34 15.0 60 41 20.0 55 40
.sup.aConcentration to 20 .times. 10.sup.6 sperm/ml was superior (P
< 0.05) to 10 .times. 10.sup.6 sperm/m1 after 48 h storage.
Also, initial dilution to 10 .times. 10.sup.6 was superior to lower
dilutions (P < 0.05). Pooled standard errors ({square root over
(error mean square of ANOVA)} / {square root over (N)} were 4.0 for
24 h, and 2.8 for 48 h incubations. .sup.bSignificant (log) linear
trend (P < 0.06).
C. CONCLUSION
[0104] High sperm dilution and cooling resulted in a substantial
reduction in the percentage of motile sperm, regardless of the
presence or removal of seminal plasma. However, this dilution
effect was greatly attenuated by concentrating the diluted sperm to
10.times.10.sup.6/ml and even more, to 20.times.10.sup.6/ml before
storage at 5.degree. C. Sperm from some bulls tolerated dilution
better than sperm from other bulls; however, the bull differences
found are typical. Extremely dilute sperm might be compromised
during sorting, in part, by removal of protective compounds in
seminal plasma.
Example 2
Effects of Equilibration Time Before Freezing Sorted Sperm
[0105] Objective: to evaluate the effect of equilibration times (3,
6 and 18 h, 5.degree. C.) before freezing on flow-sorted sperm.
[0106] The following experiment was replicated in its entirety
using the same bulls:
[0107] 1. Collection of Source Sample. Sperm of 4 bulls were
collected and prepared as described in Example 1A.
[0108] 2. Methods. [0109] a) Staining and Preparation for Sort.
[0110] i) Preparation of Stain Stock Solution: a stock solution of
8.89 mM Hoechst 33342 (bis-Benzimide H-33342; #190305, ICN
Biomedicals Inc., Aurora, Ohio) was prepared in deionized water.
[0111] ii) Sperm Stain Procedure: sperm were diluted in a modified
TALP buffer (Table 3) to 400.times.10.sup.6 sperm/ml. Following
dilution, Hoechst 33342 dye was added to the sperm suspensions at a
concentration of 224 .mu.M. After the stain was added to the sperm
suspensions, the samples were incubated for 60 minutes at
34.degree. C. Following incubation, sperm were diluted to
100.times.10.sup.6/ml with TALP containing 2.67% clarified egg yolk
and 0.002% food coloring dye (FD& C #40) which quenches the
fluorescence of Hoechst 33342 in sperm with compromised cell
membranes, allowing them to be gated out during the sorting
process. Just prior to flow sorting, samples were filtered at unit
gravity through a 40-.mu.m nylon mesh filter to remove any debris
and/or clumped sperm. [0112] b) Sorting. A two-line argon laser
operating at 351 and 364 nm and 150 mW was used to excite the
Hoechst 33342 dye. The flow cytometer/cell sorter used was an SX
MoFlo.RTM. (Cytomation, Inc., Fort Collins, Colo., USA) operating
at 50 psi, A Tris-based sheath fluid was used, consisting of Tris
(hydroxymethyl) aminomethane (Tris; 197.0 mM; #T-1503, Sigma
Chemical Co., St. Louis, Mo., USA), citric acid monohydrate (55.4
mM; #C-7129, Sigma Chemical Co., St. Louis, Mo., USA) and fructose
(47.5 mM; #F-0127, Sigma Chemical Co., St. Louis, Mo., USA).
Baseline antibiotics were also added to the Tris-based sheath fluid
consisting of 0.58 g/L of penicillin and 0.05 g/L of streptomycin
sulfate. The sperm were sorted by a process referred to as "bulk
sorting" which permits rapid accumulation of large numbers of sperm
so that large-scale examples can be done within a reasonable time.
The sperm pass through the flow cytometer under the standard
operating conditions with the exception that all droplets
containing viable sperm were collected into a single tube rather
than being sorted into 2 tubes based upon specific characteristics
(e.g., sorting by sex-type). Sperm were sorted on the basis of
viability; hence, sperm that have compromised plasma membranes were
excluded during bulk sorting.
[0113] Stained sperm were maintained at 22.+-.1.degree. C. during
sorting. Bulk sorted sperm were collected in 50-ml plastic tubes
containing 2 ml of 20% egg yolk-Tris extender prepared with 20% egg
yolk (vol/vol) in 200 mM Tris, 65 mM citric acid, 56 mM fructose,
50 .mu.g/ml tylosin, 250 .mu.g/ml gentamicin, and 150/300 .mu.g/ml
linco-spectin in deionized water. The egg yolk-Tris extender was
termed "Tris-A fraction" to denote the lack of glycerol at this
point in the procedure. Sperm were collected in tubes to contain 12
ml and approximately 6.times.10.sup.6 sperm. The sperm were
subsequently incubated at 22.degree. C. for 1 to 3 h to simulate
conditions of a sort based on sex-type. [0114] c) Preparation for
Freezing. Following incubation, the sorted sperm were cooled to
5.degree. C. over the period of 70 minutes. After cooling, the
contents of the two tubes were pooled and transferred to a
refrigerated, swinging bucket centrifuge set at 5.degree. C. and
centrifuged at 850.times.g for 20 minutes. After removing the
supernatant, processing continued at 5.degree. C. by adding about
150 .mu.l of Tris-A fraction extender to about 150-.mu.l of sperm
pellet to bring the sperm concentration to approximately
40.times.10.sup.6/ml. The sperm of individual bulls were pooled and
diluted immediately with an equal volume of egg yolk-Tris extender
containing 12% (v/v) glycerol ("Tris-B fraction"). The Tris-B
fraction was added to the sperm suspension as 2 equal volumes at
15-minute intervals to adjust the final sperm concentration to
20.times.10.sup.6/ml. The final glycerol concentration of the
complete egg yolk-Tris extender containing the sperm was 6% (v/v).
[0115] d) Equilibration and Freezing. Extended sperm were then
packaged into 0.25-ml polyvinylchloride straws to be frozen by
routine procedures on racks in static liquid nitrogen vapor. Two
straws from each of 4 bulls were frozen after 3, 6 and 18 h of
total equilibration time at 5.degree. C.
[0116] 3. Evaluation of Post-Thaw Motility. Straws were thawed in a
37.degree. C. water bath for 30 sec. Blind estimates of progressive
motility were made after incubating samples at 37.degree. C. for 0,
1 and 2 h post-thawing. Each of two observers estimated progressive
sperm motility from each of two straws of semen. These four blind
estimates for each experimental unit represent subsampling.
[0117] 4. Statistical Analysis. Statistically, the subsamples were
analyzed as a subplot to the main plot least-squares ANOVAs to
analyze effects of any observer and observer x treatment
interaction. N refers to the number of experimental units, not
subsamples; standard errors were calculated on the basis of means
of the 4 subsamples from error mean squares of ANOVAs and the
numbers of experimental units; least-squares means are
presented.
Treatment effects were evaluated via separate ANOVAs for each
incubation time. The model included bulls as a random effect and
equilibration time and observer as fixed effects; the subplot
consisted of the observer term and related interactions.
[0118] 5. Results. The 3- or 6-h equilibration times were superior
to 18-h (Table 4), based on the percentage of progressively motile
sperm, for 0 and 1 h (P<0.01) but not 2 h of post-thaw
incubation. Effects of bull were evident at 1 and 2 h incubation
times (P<0.05), but not at 0 h. There was no significant
(P>0.1) bull by equilibration time interaction nor was there a
significant observer effect for any response.
TABLE-US-00003 TABLE 3 Modified TALP Buffer Ingredient
Concentration NaCl 95.0 mM KCl 3.0 mM NaHPO.sub.4 0.3 mM
NaHCO.sub.3 10.0 mM MgCl.sub.2 .cndot. 6H.sub.2O 0.4 mM Na Pyruvate
2.0 mM Glucose 5.0 mM Na lactate 25.0 mM HEPES.sup.a 40.0 mM Bovine
serum albumin.sup.b 3.0 mg/ml Gentamycin Sulfate 30.0 .mu.g/m1
.sup.a#H3375, Sigma Chemical Co., St. Louis, MO, USA
.sup.b#US70195, fraction V; Amersham/Life Science, Cleveland, OH,
USA
TABLE-US-00004 TABLE 4 Effect of pre-freeze equilibration time on
post-thaw progressive motility (%) Equilibration Post-thaw
incubation at 37.degree. C. at 5.degree. C. 0 h 1 h 2 h 3 h
41.sup.a 36.sup.a,b 16 6 h 41.sup.a 37.sup.a 18 18 h 35.sup.b
31.sup.b 12 S.E..sup.c 1.5 0.8 2.0 .sup.a,bWithin columns, means
without common superscripts differ (P < 0.05), Tukey's HSD.
.sup.cPooled standard errors, {square root over (error mean square
of ANOVA)} / {square root over (N)}
[0119] 6. Conclusion. The results indicated no differences in
post-thaw sperm motility between 3 and 6 h of total equilibration
time at 5.degree. C., but there was a significant decline in sperm
motility following 18 h of equilibration at 5.degree. C. before
freezing. The 3- to 6-h range permits pooling 2 consecutive 3-h
sorting batches for freezing sperm without decreasing post-thaw
motility.
[0120] As the bull by equilibration-time interaction was not
significant, 3 to 6 h equilibration was adequate, with the caveat
that only 4 bulls were used. The optimum equilibration time for a
minority of bulls is expected to be >6 h.
Example 3
Effects Of Stain Concentration And Laser Power on Sorted Sperm
[0121] Objective: to evaluate the effects of Hoechst 33342 dye
concentration in combination with laser intensity on flow-sorted
sperm.
[0122] 1. Collection of Source Sample. Sperm of 6 bulls were
collected and prepared as described in Example 1A.
[0123] 2. Methods. [0124] a) Experimental Design. One ejaculate (2
bulls) and 2 ejaculates on different days (4 bulls) were used in a
2 by 2 design plus control. [0125] b) Staining and Sorting.
Staining, preparation for sorting and sorting sperm were achieved
as described in Example 2 except that the Hoechst 33342 dye was
added to sperm suspensions at a final concentration of 149 .mu.M or
224 .mu.M; and sperm were bulked-sorted with the laser operating at
100 mW or 150 mW of incident power. Bulk-sorted sperm were
collected into 50-ml plastic tubes as described in Example 2. Four
tubes containing approximately 15.times.10.sup.6 total sperm/tube
were collected over 1 h for each bull. The sorted sperm were
incubated for 1 h at 22.degree. C. to simulate a longer sorting
time. [0126] c) Preparation for Freezing. Following incubation, the
sperm were cooled as in Example 2. The sperm were then concentrated
by centrifugation at 5.degree. C. at 850.times.g for 20 minutes.
After removing the supernatant, 150 .mu.l of Tris-A fraction
extender was added to each 150-.mu.l sperm pellet at 5.degree. C.
All of the sperm pellets were suspended by gentle repeated
aspiration and the sperm of individual bulls were pooled. Tris
B-fraction extender was added stepwise as described in Example 2. A
non-stained, non-sorted control for each bull was prepared at
20.times.10.sup.6 sperm/ml in Tris extender containing 6% glycerol
and cooled to 5.degree. C. while the bulk-sorted sperm were being
prepared. [0127] d) Equilibration and Freezing. The control and
sorted sperm were packaged into 0.25-ml polyvinylchloride straws as
described in Example 2, equilibrated at 5.degree. C. for 3 h and
then frozen conventionally.
[0128] 3. Evaluation of Post-Thaw Motility. Straws were thawed and
evaluated as described in Example 2.
[0129] 4. Statistical Analysis. A general description of
statistical analyses is provided in Example 2. Specifically,
treatment effects were evaluated via ANOVA. The model included dye
concentration, laser intensity and bulls in the main plot, and
observer and related interactions in the subplot. Bulls were
considered a random effect and the other factors as fixed.
[0130] 5. Results. Bull effects were significant for percentages of
progressively motile sperm immediately after thawing (P<0.1) and
after 1 h and 2 h of incubation at 37.degree. C. (P<0.05). There
was no effect of dye concentration or bull by dye concentration on
sperm motility at any incubation time. With bulls considered as a
random effect, 150 mW of laser power resulted in lower post-thaw
motility of sperm than 100 mW at 0 h of incubation (P<0.1), but
not at other incubation times (Table 5). If bulls are considered as
fixed effects, 150 mW of power resulted in lower sperm motility
than 100 mW (P<0.05) at all 3 incubation times. There was an
effect of bull by laser power (P<0.05) on sperm motility at 1 h,
but not at 0-h or 2-h incubation times. Also, the higher laser
power resulted in lower sperm motility than the control (P<0.05)
at 0- and 1-h incubation times (Table 5). There was a significant
observer effect at 1-h, but not at 0-h or 2-h, incubation times.
There was no observer by treatment interaction (P>0.1).
TABLE-US-00005 TABLE 5 Effects of laser intensity and dye
concentration on post-thaw motility (%). Incubation at 37.degree.
C. Main effect means 0 h 1 h 2 h Control 49 44 33 Dye Concentration
149 .mu.M 41 39 30 224 .mu.M 42 39 30 Laser Intensity 100 mW 46 42
33 150 mW 38.sup.a 35.sup.b 27 S.E..sup.c 2.2 1.2 1.3
.sup.aSignificant main effect (P < 0.1) and differs from control
(P < 0.05). .sup.bDiffers from control (P < 0.05).
.sup.cPooled standard errors, {square root over (error mean square
of ANOVA)} / {square root over (N)}
[0131] 6. Conclusion. Percentages of progressively motile sperm
post-thaw were diminished by the staining and sorting process.
Higher laser intensity was more damaging than the lower laser
intensity. There was no effect of dye concentration on post-thaw
sperm motility. Thus, excitation of the sperm-bound Hoechst 33342
dye at lower laser intensities is less damaging and that staining
sperm at the higher dye concentration had no detrimental effect on
post-thaw motility. The damage observed was presumably to the
sperm-motility apparatus.
Example 4
Evaluation of Pre-Sort Staining Procedures and Selection of
Extenders for the Cryopreservation Of Sperm
[0132] Objective: (1) to evaluate three pre-sort treatments for
sperm; and, (2) and to evaluate sheath fluid and extender
combinations for the cryopreservation of flow-sorted sperm. The
following experiment was replicated in its entirety:
[0133] 1. Collection of Source Sample. Sperm from 4 bulls were
collected and prepared as described in Example 1A.
[0134] 2. Methods. [0135] a) Experimental Design. A 3 (pre-sort
treatments) by 3 (extenders) by 2 (sheath fluids) by 4 (bulls) by 2
(observers) factorial experiment was designed to determine the best
procedure to hold sperm prior to sorting, and to evaluate three
extenders for cryopreserving the sorted sperm. [0136] b) Sample
Preparation and Staining. Freshly collected sperm from each of 4
bulls were treated as follows: [0137] (1) diluted to
400.times.10.sup.6/ml in modified TALP (see Example 2, Table 3) and
stained for 1 h at 34.degree. C. before bulk-sorting ("Dilute-0
h"); [0138] (2) incubated neat at 22.degree. C. for 3 h before
dilution, staining and sorting ("Neat-3 h"); or, [0139] (3) diluted
and stained as "Dilute-0 h and then incubated at 22.degree. C. for
3 h before bulk-sorting ("Diluted-3 h"). [0140] c) Extenders. The
following freezing extenders were compared: EYC (see Example 1)
containing 7% glycerol, egg yolk-Tris (see Example 2) containing 6%
glycerol, and egg yolk-TES-Tris (TEST) containing 5% glycerol. EYC
"A Fraction" refers to the EYC extender containing no glycerol, and
EYC "B Fraction" refers to EYC extender containing twice the final,
desired glycerol concentration (i.e., 14%). Thus, when EYC A and B
fractions are combined in equal volume, the final EYC extender
contains 7% glycerol. Tris A and B fractions are similarly named,
and described in Example 2. TEST extender is prepared as a complete
extender containing 5% glycerol; hence, there were no "A" and "B"
fractions for TEST. [0141] d) Sheath Fluid. Sheath fluid was either
98.6 mM sodium citrate dihydrate (#S279-3, Fisher Scientific, Fair
Lawn, N.J.) or Tris as described in Example 2. Both types of sheath
fluid were adjusted to pH 6.8; osmolality was about 270 to 280
mOsm/kg. Tris sheath fluid was used to collect sperm that were
later extended in egg yolk-Tris and TEST freezing extenders. Sheath
fluid containing 98.6 mM sodium citrate dihydrate was used to
collect sperm to later be extended in EYC freezing extender. [0142]
e) Sorting. Approximately 58.times.10.sup.6 sperm for each
combination of pre-sort treatment, sheath fluid and extender were
bulk-sorted as described in Example 2 using 150 mW of incident
laser power. For each sort, sperm were collected over approximately
1 h. After sorting, the samples were incubated at 22.degree. C. for
2 h to simulate a 3 h sort. [0143] f) Preparation for Freezing.
Following incubation, the sperm were cooled as described in Example
2. After cooling, the samples were centrifuged at 5.degree. C. at
850.times.g for 20 min. Each sample comprised about 28 ml total
volume and was contained in a 50-ml plastic tube [0144] After the
supernatant was removed, the sperm were returned to a 5.degree. C.
cold room for extension. Samples were extended to
40.times.10.sup.6/ml by depositing 131 .mu.l of the sperm
suspension into 69 .mu.l of A-fraction EYC, A-fraction egg yolk
Tris, or TEST extender. Immediately, suspensions were adjusted to
20.times.10.sup.6 sperm/ml with the addition of the matched
glycerol containing extender (i.e., B-fraction EYC, B-fraction
Tris) or TEST. B-fraction extenders were added to their respective
samples stepwise (2.times.) at 15-min intervals as described in
Example 2. The TEST was added to sperm stepwise in the same manner
as B fraction EYC and Tris extenders. [0145] g) Equilibration and
Freezing. Sperm were packaged into 0.25-ml polyvinylchloride
straws, equilibrated for 3 h at 5.degree. C. and then frozen in
static liquid nitrogen vapor.
[0146] 3. Evaluation of Post-Thaw Motility. Thawing and post-thaw
evaluations of sperm were done as described for Example 2.
[0147] 4. Statistical Analysis. A general description of
statistical analyses is provided in Example 2. Specifically,
treatment effects were evaluated via separate analyses of variance
for each post-thaw incubation time. The main plot included pre-sort
treatment, extenders, and bulls; the subplot consisted of observers
and associated interactions. Bulls were considered a random effect,
and the other factors, fixed. The entire experiment was replicated
twice. Tukey's HSD test was used to separate means.
[0148] 5. Results. Post-thaw progressive motility of bulk-sorted
sperm was affected (P<0.05) by extender and bulls at each
post-thaw incubation time and by pre-sort procedure at 0 h of
incubation (Table 6). There were no differences due to sheath
fluids (P>0.05). At 0-h post-thaw incubation, use of the neat-3
h treatment resulted in more motile sperm after freezing and
thawing than the other 2 pre-sort staining treatments (P<0.05;
Table 6). However, pre-sort procedures were not statistically
significant after post-thaw incubation of sperm for 1 or 2 h with
bulls considered as a random effect. Importantly, at these 2
incubation times, there were significant pre-sort treatment by bull
interactions (P<0.05). Furthermore, pre-sort treatment would
have been a significant effect at all post-thaw incubation times
had bulls been considered as fixed effects.
[0149] Immediately after thawing (0 h), TEST was the best extender,
but after 1 or 2 h of incubation of 37.degree. C., Tris was the
best extender. Importantly, there was no pre-sort treatment by
extender interaction for any response. There were observer effects
(P<0.01) at all incubation times, but no observer by treatment
interactions. There was a bull by extender interaction (P<0.05)
at all 3 incubation times.
TABLE-US-00006 TABLE 6 Main effects of pre-sort treatment and
freezing extenders on post-thaw progressive motility (%) Incubation
at 37.degree. C. Pre-sort procedure Extender 0 h 1 h 2 h Dilute - 0
h Mean 39.sup.a 32 22 Neat - 3 h Mean 43.sup.b 36 25 Dilute - 3 h
Mean 38.sup.a 31 19 Mean EYC 36.sup.a 29.sup.a 17.sup.a Mean Tris
40.sup.b 39.sup.b 29.sup.b Mean TEST 44.sup.c 33.sup.c 20.sup.a
S.E..sup.d 0.8 0.8 0.7 .sup.a,b,cMeans within columns, within main
effects, without common superscripts differ (P < 0.05).
.sup.dPooled standard errors {square root over (error mean square
of ANOVA)} / {square root over (N)}
[0150] 6. Conclusion. This study showed that holding sperm neat for
3 h before dilution, staining and sorting was better than immediate
dilution and staining 0 h or 3 h later. Thus, by 3 h into the sort,
it is best to continue with a new aliquot of the original ejaculate
that was held neat 3 h and then stained, rather than continuing
with the original sample of sperm stained and held at
400.times.10.sup.6 sperm/ml.
[0151] Even though TEST extender provided higher pott-thaw motility
at 0 h, Tris was the superior extender when sperm were stressed by
incubation at 37.degree. C. Either sheath fluid worked equally well
for each extender. Based on these results, we have incorporated the
use of Tris sheath fluid in combination with Tris freezing extender
into our standard operating procedure.
Example 5
Effects Of Extender Additives on Sorted Sperm
[0152] Objective: to evaluate the effect of adding sodium dodecyl
sulfate ("SDS") to the freezing extender on flow-sorted sperm.
A. Evaluation of Effect of Concentration of SDS in Freezing
Extender
[0153] 1. Collection of Source Sample. Sperm of 6 bulls were
collected and prepared as described in Example 1A.
[0154] 2. Methods. Sperm from each of 6 bulls were extended to
20.times.10.sup.6/ml in 20% whole egg Tris ("WET") extender
containing 0, 0.03, 0.06, 0.09, or 0.12 percent SDS, packaged into
straws and frozen. WET extender was prepared using 3.028 g of
Tris[hydroxymethyl] aminomethane, 1.78 g of citric acid
monohydrate, and 1.25 g of fructose per 100 ml of double distilled
water, to which 20% whole egg (vol/vol) was added. The WET extender
was prepared at a pH of about 7.0 and contained a final glycerol
concentration of about 6% (vol/vol). The WET extender also
contained 1000 IU of penicillin "G" sodium and 100 .mu.g of
streptomycin sulfate/ml.
[0155] 3. Results. The respective means (n=1 sample from each of 6
bulls) were 51, 51, 50, 51, and 48% progressive motile sperm
approximately 10 minutes post-thaw. Based on these results, 0.06
percent SDS was used in Example 5B.
B. Evaluation of the Effects of 0.06 Percent SDS in Various
Freezing Extenders on Post-Thaw Motility of Flow-Sorted Sperm
[0156] 1. Collection of Source Sample. Sperm of 8 bulls were
collected and prepared as described in Example 1A.
[0157] 2. Methods. Post-thaw motility was studied for sperm frozen
in egg yolk-Tris (see Example 2) and WET extenders (see Example 5A)
with and without 0.06% SDS. Final glycerol content for both
extenders was 6%. [0158] a) Staining. Preparation for Sort,
Sorting. Stained sperm samples were prepared from an ejaculate from
each of 8 bulls as described in Example 2. Stained sperm were
bulked-sorted using Tris sheath fluid as described in Example 2
except that the sort was achieved using 135 mW of incident laser
power. Sorted sperm were collected in a 50-ml plastic tube
containing 2 ml of A-fraction freezing buffer for each extender;
15.times.10.sup.6 total sorted sperm (25 ml) for each treatment
were collected and incubated for 1 h at 22.degree. C. to simulate
longer sorting. [0159] b) Preparation for Freezing. Diluted sperm
were then cooled to 5.degree. C. over minutes. An equal volume of
appropriate B-fraction extender was added stepwise (2.times.) at
15-minute intervals to each 50-ml plastic tube containing sorted
sperm. Aliquots, of 25 ml/extender treatment were concentrated by
centrifugation for 20 minutes at 850.times.g in a refrigerated
centrifuge. The supernatant was removed leaving a 600 .mu.L sperm
pellet, which was suspended by gentle vortexing for 15 seconds. No
additional extender was added to the sperm pellet since the
suspension containing the pellet already contained glycerol. The
concentration of the sperm suspension was approximately
20.times.10.sup.6/ml. A non-stained, non-sorted control for each
bull was prepared at 20.times.10.sup.6 sperm/ml in egg-yolk-Tris
extender containing 6% glycerol. The control was placed in a
5.degree. C. cold room while bulk-sorting occurred. [0160] c)
Equilibration and Freezing. All control and bulk-sorted sperm were
packaged and frozen at the same time. Sperm were packaged into
0.25-ml polyvinylchloride straws, equilibrated for about 3 h to
about 6 h at 5.degree. C. and then frozen in static liquid nitrogen
vapor.
[0161] 3. Evaluation of Post-Thaw Motility. Thawing and post-thaw
evaluations of sperm were done as described for Example 2 with the
exception that progressive motility was evaluated 0.5 and 2.0 h
after incubation.
[0162] 4. Statistical Analysis. A general description of
statistical analyses is provided in Example 2. Specifically,
treatment effects were evaluated via separate analyses of variance
for each incubation time; the model included bull and extender in
the main plot and observer and related interactions in the subplot.
Differences in means were determined by the least significant
difference test.
[0163] 5. Results. Extender affected (P<0.05) progressive
motility of sperm after 0.5 or 2 h post-thaw incubation (Table 7).
At 0.5 h, WET plus SDS resulted in lower motility than Tris with
SDS. At 2 h, all treatments with bulk-sorted sperm were worse than
the non-sorted control sperm. There were significant bull and
observer effects (P<0.01) at both incubation times, but no
observer by treatment interactions.
TABLE-US-00007 TABLE 7 Effect of extender on post-thaw progressive
motility (%) Incubation at 37.degree. C. Extender 0.5 h 2 h Tris
(non-sort) 42.sup.a 41.sup.a Tris w/o SDS 40.sup.a,b 35.sup.b Tris
w/SDS 42.sup.a 37.sup.b WET w/o SDS 40.sup.a,b 35.sup.b WET w/SDS
38.sup.b 35.sup.b S.E..sup.c 1.0 1.2 .sup.a,bMeans within columns
without common superscripts differ (P < 0.05). .sup.c{square
root over (error mean square of ANOVA)} / {square root over
(N)}
[0164] 6. Conclusion. The inclusion of SDS in Tris or WET extenders
did not benefit sperm quality as determined by visual estimates of
motility after thawing. Also, results using WET and Tris extenders
were similar; hence, WET appeared as efficacious as Tris for
cryopreserving sorted bovine sperm.
Example 6
Quality of Sperm Sexed by Flow Sorting for Field Trials
[0165] Objective: to evaluate post-thaw quality of sorted sperm
based on acrosomal integrity.
[0166] 1. Collection of Source Sample. Sperm of 3 bulls were
collected and prepared as described in Example 1A.
[0167] 2. Methods. Sorted and non-sorted control sperm from the
same ejaculate were stained, processed, and sorted as described in
Example 2 except the sperm were sorted for sex-type at a 90% purity
level. Sorted sperm were collected to a volume of approximately 20
ml and were cooled to 5.degree. C. for 90 minutes (0.2.degree.
C./min). After cooling, an equal volume of egg yolk-Tris B extender
(see Example 2) was added to the sorted sperm in 2 equal volumes at
15-minute intervals. Centrifugation and aspiration of the
supernatant were achieved as described in Example 5. After
centrifugation and aspiration, egg yolk-Tris extender containing 6%
glycerol (v/v) was added to the sperm pellet to bring the
concentration of sperm to about 20.times.10.sup.6/ml. Freezing and
thawing were done as described in Example 2 except that
equilibration time was about 3 h.
[0168] 3. Evaluation of Post-Thaw Motility. Visual estimates of the
percentage of progressively motile sperm at 37.degree. C. were made
approximately 10 minutes after thawing. The acrosomal integrity of
sperm was assessed using differential interference-contrast
microscopy (.times.1000) after 2 h of incubation at 37.degree. C.
Sperm were treated with 40 mM sodium fluoride, a wet was smear
made, and 100 sperm per treatment were examined. Acrosomes were
classified as: (a) intact acrosome, (b) swollen or damaged
acrosome, or (c) missing acrosome (non-intact).
[0169] 4. Statistical Analysis. The data analyzed were from 19
different freeze dates balanced across 3 bulls used in field
trials. Treatment effects (sort vs. control) were evaluated via
analysis of variance with bulls as a fixed effect.
[0170] 5. Results. The percentage of progressively motile sperm
post-thaw was significantly higher (P<0.05) for non-sorted sperm
(50%) than for sorted sperm (46%; Table 8), despite removal of dead
sperm during sorting. However, the percentage of sperm with an
intact acrosome was not different. Sorting increased the percentage
of sperm missing an acrosome, but also reduced the percentage of
sperm with a damaged acrosome, relative to control sperm
(P<0.05). There were significant differences among bulls for
percent of intact acrosomes (P<0.05), percent of non-intact
acrosomes (P<0.01), and post-thaw progressive motility
(P<0.01). There was a bull by sorting effect for post-thaw
motility (p<0.01) but not for the other responses. From bulls A
and B, differences in post-thaw motility between sorted and
unsorted sperm were near zero; for bull C, sorted sperm were 10
percentage points (19%) lower in motility than control sperm.
TABLE-US-00008 TABLE 8 Effect of sorting on post-thaw motility (%)
and acrosomal status (%) Acrosomal status Intact Damaged Non-intact
Post-thaw motility Control 64.sup.a 20.sup.a 15.sup.a 50.sup.a
Sorted 65.sup.a 14.sup.b 21.sup.b 46.sup.b .sup.a,bColumn means
with different superscripts differ (P < 0.05).
[0171] 6. Conclusion. Visual estimates of progressive motility for
sorted, frozen sperm on average were slightly lower (4 percentage
points; 8%) than for control sperm, although this difference was
larger for one bull. These evaluations were made approximately 10
minutes after thawing. The small average difference is consistent
with that for non-intact acrosomes after 2 h of incubation. Sperm
with a damaged or missing acrosome are likely to be immotile. The
increased percentage of sperm with a non-intact acrosome, for
sorted samples, indicates damage associated with sorting or with
cryopreservation before or after actual sorting. Presumably,
sorting converted damaged acrosomes to missing acrosomes. Based on
standard procedures for evaluation of sperm quality, there is no
basis for assuming that fertilizing potential of these flow-sorted
sperm should be severely compromised for most bulls.
Example 7
Sex-Selection and Cryopreservation of Bull Sperm Using 20% Egg
Yolk-Tris Extender
[0172] Objective: to provide a protocol for the cryopreservation of
flow-sorted bull sperm.
[0173] 1. Collection and Ejaculate Assessment. Collect and prepare
ejaculates as described in Example 1A. Select ejaculates from those
bulls with >75% morphologically normal sperm. Visually estimate
the percentage of progressively motile sperm (ejaculates that have
progressive motility >60% are best for sorting). Add antibiotics
to raw semen as follows: tylosin at a final concentration 100
.mu./ml, gentamicin at a final concentration of 500 .mu.l, and
linco-spectin at a final concentration of 300/600 .mu.g/ml.
[0174] 2. Staining and Preparation for Sort. Following the addition
of the antibiotics to the raw semen sample, allow 15-20 minutes
before staining. Stain samples as described in Example 2.
[0175] 3. Sorting. Sort for both X- and Y-type sperm, setting the
sorting gates for 90% purity. Sort sperm into 50-nil Falcon tubes
containing 2 ml 20% egg yolk-Tris A-fraction extender (see Example
2) until each tube contains a maximum of 20 ml total volume (or a
maximum of 2 h per sort) and final sorted sperm concentration is
6.times.10.sup.5/ml. Note that additional 20% egg yolk-Tris-A
fraction catch buffer must be added after the sort and prior to
cooling so that the final percentage of egg yolk is at least
3%.
[0176] 4. Preparation for Freezing. Following the sort, cool the
sorted samples to 5.degree. C. over a period of 90 minutes. After
cooling, add 20% egg yolk-Tris B-fraction extender (see Example 2)
stepwise (2.times.) at 15 minutes intervals. The final volume of
Tris B-fraction extender added to the sperm sample should be equal
to the volume of Tris A-fraction extender. The total volume of
sperm sample after the Tris B-fraction extender is added should not
exceed 27 ml total volume.
[0177] After the Tris B-fraction extender is added to the sperm
sample, concentrate the sample by centrifugation for 20 minutes at
850.times.g. Aspirate the supernatant leaving approximately 150
.mu.l sperm pellet. Resuspend the sperm and pool the sperm for each
individual bull.
[0178] 5. Freezing. Add complete egg yolk-Tris extender (6%
glycerol) to achieve a final sperm concentration of
20.times.10.sup.6/ml. Package the extended sperm into 0.25-ml
polyvinylchloride straws for freezing as described in Example
2.
Example 8
Evaluation of the Fertility of Flow-sorted, Frozen Bull Sperm in
Field Studies
Materials and Methods
Semen Collection and Processing
[0179] Semen from young bulls of unknown fertility was collected
via artificial vagina (see Example 1A). After determining sperm
concentration with a spectrophotometer and subjective evaluation of
progressive sperm motility, semen was processed and sorted as
described in Example 2 except that the sperm were sorted by
sex-type at 90% purity using a laser incident power of about 135 to
about 150 mW. Processing and freezing was achieved as in Example 2
except that the equilibration time was about 3 h. Cornell Universal
Extender (Seidel G E Jr., Theriogenology 1997; 48:1255-1264) was
used for liquid semen in field trials 1, 2, and 3. For frozen semen
in field trials 2 and 3, the extender used was 2.9% Na citrate+20%
egg yolk with a final glycerol concentration of 7% (see Example 1).
For field trials 4 through 11, sperm were frozen in a Tris-based
extender composed of 200 mM Tris, 65 mM citric acid, 56 mM
fructose, 20% egg yolk, and a final glycerol concentration of 6%
(see Example 2). The sheath fluid used in the flow cytometer was
2.9% Na citrate (see Example 4) for trials 1, 2, and 3, and a Tris
buffer for the remaining trials (see Example 2).
[0180] Sperm were packaged in 0.25-mi French straws in columns as
small as 50 .mu.l in the center of the straw. To minimize dilution
effects, low volumes were used so there were at least 10.sup.7
sperm/ml. In most trials, a column of extender without sperm was
aspirated into the straw first to wet the cotton plug, followed by
a small column of air, and then the sexed sperm. When sperm were
frozen, one straw from each batch was thawed in 35.degree. C. water
for 30 sec for quality control, and batches with less than 25%
progressive motility post thaw were discarded. A sample of sexed
sperm from each batch was sonicated and analyzed by flow cytometry
to determine the accuracy of sexing.
Heifer Management and Artificial Insemination
[0181] The heifers used were in 6 widely scattered production units
with different management practices. Seasonal and breed differences
contributed further to the heterogeneity of the experiments (Table
9). Insofar as possible, treatments and controls were alternated
systematically within bulls within inseminators as heifers entered
the insemination facilities.
[0182] Estrus was synchronized in one of 4 ways (Table 9): (1) 500
mg of melengesterol acetate (MGA) fed daily in 2.3 kg of grain for
14 days followed by an i.m. injection of 25 mg prostaglandin
F.sub.2.alpha. (Lutalyse, Upjohn, Kalamazoo, Mich., USA) 17, 18 or
19 days after the last day of feeding MGA (MGA/PG); (2) a single
injection of 25 mg of prostaglandin F.sub.2.alpha. (PG); (3) 20 or
25 mg of prostaglandin F.sub.2.alpha. injected i.m. at 12-day
intervals (PG/PG) or (4) 50 or .mu.g of GnRH injected i.m.,
followed by 25 mg of prostaglandin F.sub.2.alpha. 7 days later
(GnRH/PG).
[0183] Heifers were inspected visually for standing estrus mornings
and evenings, but inseminated only in the evenings after 16:00,
approximately 1/2 or 1 day after onset of estrus. Insemination was
either into the uterine body conventionally, or half into each
uterine horn using atraumatic embryo transfer sheaths (IMV,
Minneapolis, Minn., USA). In the latter case, semen was deposited
past the greater curvature of the uterine horn as far anterior as
could be accomplished without trauma, identically to nonsurgical
embryo transfer. In most cases, semen was deposited between the
anterior third and mid-cornua.
[0184] Most experiments included a frozen sperm control inseminated
into the uterine body with 20 or 40.times.10.sup.6 sperm/dose from
the same bulls used for sperm sorted for sex-type ("sexed"). This
control served as a composite estimate of the intrinsic, normal
fertility of the heifers under the specific field-trial conditions
as well as the fertility of the bulls used and the skills of the
inseminators. Some trials also included a low-dose, unsexed control
group. Sometimes numbers of control inseminations were planned to
be 1/2 or 2/3 the number used for each treatment to obtain more
information on sexed sperm. Frozen sexed and control sperm were
thawed for 20 to 30 sec in a 35 to 37.degree. C. water bath.
Various other details are summarized in Table 9.
[0185] Pregnancy was diagnosed by ultrasound 28 to 37 d post
insemination and/or 56 to 92 d post-insemination, at which time
fetal sex was determined in most trials, as described in Curran,
S., Theriogenology 1991; 36:809-814, without the operator's knowing
insemination treatments of controls. Sexes of calves born were
nearly identical to the fetal-sex diagnosis. Data were analyzed by
single-degree-of-freedom Chi square corrected for continuity;
2-tail tests were used unless 1-tail is specified. Fewer than 5% of
the inseminations were culled due to errors of insemination
treatment, frank infection of the reproductive tract, failure to
traverse the cervix, etc. Decisions to cull animals from
experiments were made shortly after insemination and were never
based on the pregnancy diagnosis.
TABLE-US-00009 TABLE 9 Procedural details of field trials
Insemination Breeds of Estrus Trial dates heifers Bulls used
Inseminators synchronization Comments 1 5/20-23, Angus N1, N2, AN4
A, B MGA/PG Included low- 1997 dose controls 2 2/18-5/22, Angus N3,
N4, N5, C, D PG/PG Low dose but no 1998 crossbred N6 normal-dose
controls; some heifers pregnant and aborted when synchronized 3
6/2-6/5, Angus AN4, AN5, B, D MGA/PG 1998 N7, N8 4 2/10-13,
Holstein J2, J4 C, D PG Very severe 1999 mud, snow, wind, and cold,
driving rain 5 2/24-26, Holstein J2, J4, J5 C, B, D PG/PG 1999 6
4/14-16, Holstein J2, J3, J4, J5 C, D PG Some heifers 1999 were
reproductive culls 7 4/27-5/1, Hereford& AN1, AN4 C MGA/PG
Semen for 1 bull 1999 Angus shipped 6 h crossbred before sorting;
severe weather 8 4/21-5/1 Angus H1, H2 E MGA/PG Feedlot heifers
1999 crossbred 9 5/5-8, 1999 Red Angus AR1, AR2 C, F MGA/PG 10
5/31-6/2 Angus AN4, AN7, B, D GnRH/PG 1999 AN8 11 7/28-30 Holstein
H2, H3 C, D PG/PG First replicate 1999 available in a much larger
trail
Results and Discussion
[0186] The data presented are from 11 consecutive, heterogeneous
field trials, constrained by logistical aspects of the studies,
such as having to match bulls to genetic needs of the herds,
unavailability of fertility information on bulls, limited numbers
of heifers, unavailability of the same inseminators across trials,
severe weather in some trials, limited amounts of sexed semen in
early trials, 2 sets of heifers in which some turned out to be
pregnant up to about 55 days at the time of estrus synchronization,
etc. Up to 4 bulls and 3 inseminators were involved with each
trial; this enabled us to sample populations to ensure that results
applied to more than one bull or technician; however, insufficient
data were produced to evaluate bull-to-bull differences in
fertility rigorously.
[0187] Most sets of heifers were from breeding herds located 140 to
250 km from our laboratory. There were no significant differences
in pregnancy rates between inseminators in any trial, but numbers
of breedings per inseminator were low, and differences likely would
be detected with larger numbers of inseminations.
[0188] Estrus synchronization methods were not compared within
trials, so it was not possible to compare pregnancy rates among
these methods. Pregnancy rates appeared to be satisfactory for all
four synchronization procedures used.
[0189] Since inseminations were done once a day, heifers in estrus
evenings were inseminated approximately 24 h after estrus was
detected. The pregnancy rate for these heifers with sexed sperm
pooled over all trials was 203/414 (49.0%), which was not
significantly different (P>0.1) from that of heifers in estrus
mornings and thus inseminated half a day after estrus detection
266/586 (45.4%). This tendency for higher fertility with later
insemination is in agreement with findings from other research that
it is preferable to inseminate later than normally recommended with
lower fertility bulls, when low sperm numbers are used, or when
conditions are otherwise suboptimal.
[0190] Pregnancy rates by treatments and, when available, fetal or
calf sex are presented in Tables 10 to 20. The objective was to
obtain female offspring, except in trial 8; accuracy was 95%, 83%,
90%, 83%, 82%, and 94% in Trials 1, 3, 8, 9, 10, and 11,
respectively. In the remainder of the trials, fetal or birth sexes
were not available because of timing of pregnancy diagnosis,
unavailability of persons skilled in sexing fetuses, and/or because
calves have not yet been born. This was not a major concern because
the main objective of this research was to determine fertility of
flow-sorted sperm inseminated at low doses.
[0191] The accuracy of sexing can be adjusted to virtually any
level desired between 50 and 95+% by adjusting the sorting
parameters. However, higher accuracy results in lower numbers of
sperm sorted per unit time, particularly for Y-chromosome sperm.
90% accuracy is sufficient for routine work.
[0192] The main findings from each field trial will be summarized
in turn. Note that total sperm numbers are given in table headings;
numbers of progressively motile sperm usually were 30 to 50% of
these values. Field trial 1 (Table 10) confirmed that pregnancy
rates with uterine horn insemination using low numbers of unsexed
sperm were similar to controls with normal sperm numbers. The day
64 to 67 pregnancy rate with unfrozen sexed sperm (42%) was 12
percentage points below the unsexed liquid control with sperm
diluted, stained, and centrifuged identically to the sorted sperm.
Accuracy of sexing was 95%; the sex of calves born from sexed sperm
matched the sex diagnosis of fetuses exactly; there was one mistake
in sexing fetuses of controls. There were no abortions between 2
months of gestation and term, and all 19 calves from the sexed
sperm treatment were normal and survived. For the sexed semen
treatment, the 2-month pregnancy rates for bulls N1, N2, and N3
were 41, 44, and 40%, respectively; 39% (13/33) of heifers in
estrus in the morning and 50% (6/12) in estrus in the evening
became pregnant.
TABLE-US-00010 TABLE 10 Results of field trial 1 -- Angus heifers
in Wyoming, 1997 No. pregnant Treatment/ No. No. day 31 to No.
pregnant No. site sperm heifers 33 day 64 to 67 calves Sexed, 3
.times. 10.sup.5 45 20(44%) 19(42%) 18(95%).sup.a 5.degree.
C./horns Control, 3 .times. 10.sup.5 28 15(54%) 15(54%)
5(53%).sup.b 5.degree. C./horns Frozen 40 .times. 10.sup.6 29
16(55%) 15(52%) 11(73%).sup.a,b control/body .sup.a,bSex ratios
without common superscripts differ (P < 0.02).
[0193] Field trial 2 (Table 11) provided the first evidence that
results with sexed, frozen sperm are similar to sexed, unfrozen
sperm if adjustment is made for numbers of sperm killed during
cryopreservation. There also was no difference in pregnancy rates
between sexed sperm stored at 5 versus 18.degree. C. Pregnancy
rates at 2+ months after insemination for sexed semen from
individual bulls ranged from 22 to 42% pregnant (P>0.05).
Embryonic loss between 1 and 2 months of gestation was very similar
for sexed and control pregnancies. Calving data were available from
39 heifers from this trial; each of these heifers (30 sexed
pregnancies, 9 controls) pregnant at 2 months calved after a
normal-length gestation.
TABLE-US-00011 TABLE 11 Results of field trial 2-Crossbred beef
heifers in Colorado, 1998 No. No. No. pregnant No. pregnant
Treatment/site sperm heifers day 30 to 35.sup.a day 59 to 92.sup.a
Control, 5.degree. C./horns 5 .times. 10.sup.5 58 27 (47%) 24 (41%)
Sexed, 5.degree. C./horns 5 .times. 10.sup.5 51 17 (33%) 16 (31%)
Sexed, 18.degree. C./horns 5 .times. 10.sup.5 46 16 (35%) 12 (26%)
Sexed, frozen/horns 1 .times. 10.sup.6 87 29 (33%) 28 (32%)
.sup.aNo significant differences, .chi..sup.2
[0194] Field trial 3 (Table 12) confirmed that sexed, frozen sperm
results in reasonable pregnancy rates. The accuracy of sexing sperm
was confirmed again; however, there were 4 errors in sexing fetuses
relative to the calves born; the actual sexes of calves born are
presented. Again, there were no abortions between 2 months of
gestation and term. Pregnancy rates averaged over sexed, unfrozen
and sexed, frozen sperm for bulls N8, N9, AN5, and AN4 were 24; 31,
50, and 60%, respectively (P<0.1).
TABLE-US-00012 TABLE 12 Results of field trial 3 -Angus heifers in
Wyoming, 1998 No. No. No. pregnant No. Treatment/site sperm heifers
day 62 to 65 calves Sexed, 18.degree. C./horns 5 .times. 10.sup.5
37 11 (30%).sup.a 10 (91%).sup.c Sexed, frozen/horns 1 .times.
10.sup.6 35 18 (51%).sup.a,b 14 (78%).sup.c Frozen, control/body 40
.times. 10.sup.6 37 27 (73%).sup.b 16 (59%).sup.d .sup.a,bMeans
without common superscripts differ P < 0.05). .sup.c,dThe
percentage of calves from the sexed treatments (83%) differed from
the control group, P > 0.05, 1-tail, .chi..sup.2.
[0195] Field trials 4, 5, and 6 (Tables 13, 14, 15) were done at
the same location with 3 different groups of heifers.
Unfortunately, it was not possible to replicate each trial
similarly due to vagaries of field trials, such as scheduling
personnel, availability of sexed semen from each bull, etc. The
widely different pregnancy rates between trials 5 and 6 illustrate
that conditions were different among trials. Some of the heifers in
trial 6 were available because they failed to get pregnant after a
month of natural mating. Under conditions of these trials,
pregnancy rates were very similar between 1.5 and
3.0.times.10.sup.6 sexed, frozen sperm/dose. Furthermore, there was
no advantage to uterine-horn insemination. There were no
significant differences (P>0.05) in pregnancy rates among bulls
except in Trial 5 in which the pregnancy rate of J2, 20/28 (71%),
was higher than that of J4, 15/39 (38%) (P<0.05). This
difference was not consistent from trial to trial, as J4 had
numerically but not significantly (P>0.1) higher pregnancy rates
than J2 in Trials 4 and 6.
TABLE-US-00013 TABLE 13 Results of field trial 4-Holstein heifers
in Colorado, 1999 No. No. No. pregnant No. pregnant Treatment/site
sperm heifers day 30 to 33 day 64 to 67* Sexed, frozen/body 1.5
.times. 10.sup.6 55 36 (65%).sup.a,b 36 (65%).sup.a,b Sexed,
frozen/body .sup. 3 .times. 10.sup.6 52 27 (52%).sup.a 26
(50%).sup.a Control, 20 .times. 10.sup.6 55 45 (82%).sup.b 43
(78%).sup.b frozen/body .sup.a,bMeans without common superscripts
differ (P < 0.01). *Six heifers pregnant at d 30 to 33 were sold
before the second pregnancy diagnosis; these were assumed to have
remained pregnant.
TABLE-US-00014 TABLE 14 Results of field trial 5 - Holstein heifers
in Colorado, 1999 No. No. No. pregnant No. pregnant Treatment/site
sperm heifers day 33 to 35.sup.a day 60 to 62.sup.a Sexed,
frozen/body 1.5 .times. 10.sup.6 23 12 (52%) 12 (52%) Sexed,
frozen/body 3.0 .times. 10.sup.6 25 15 (60%) 14 (56%) Sexed,
frozen/horns 1.5 .times. 10.sup.6 25 15 (60%) 12 (48%) Sexed,
frozen/horns 3.0 .times. 10.sup.6 25 17 (68%) 15 (60%) Control, 20
.times. 10.sup.6 30 20 (67%) 19 (63%) frozen/body .sup.aNo
significant differences.
TABLE-US-00015 TABLE 15 Results of field trial 6 - Holstein heifers
in Colorado, 1999 No. No. No. pregnant No. pregnant Treatment/site
sperm heifers day 31 to 34 day 60 to 63 Sexed, frozen/body 1.5
.times. 10.sup.6 27 11 (41%).sup.a 9 (33%).sup.a Sexed, frozen/body
3.0 .times. 10.sup.6 25 10 (40%).sup.a 9 (36%).sup.a Sexed,
frozen/horns 1.5 .times. 10.sup.6 24 8 (33%).sup.a 7 (29%).sup.a
Sexed, frozen/horns 3.0 .times. 10.sup.6 24 10 (42%).sup.a 8
(33%).sup.a Control, 20 .times. 10.sup.6 24 18 (75%).sup.b 17
(71%).sup.b frozen/body .sup.a,bMeans without common superscripts
differ (P < 0.05).
[0196] For trial 7 (Table 16), only one inseminator was available
due to rescheduling. This is the only trial that showed a
convincing advantage of uterine-horn over uterine-body
insemination. For this inseminator under the conditions of the
trial, 55% more heifers (22 percentage points) became pregnant with
sexed, frozen semen inseminated into the uterine horns than into
the uterine body. The true difference could be smaller because
there are wide confidence intervals on these means. In all the
other trials (5, 6, 9, and 11) in which body- and horn-insemination
were compared, pregnancy rates were very similar for both methods
for this technician as well as for other technicians.
[0197] Semen from one of the bulls used in Trial 7 was shipped
without dilution from Montana by air in an insulated box at
-20.degree. C. before sorting; shipping time was 6 h. Pregnancy
rates for the sexed sperm from the two bulls were virtually
identical, 49% for the unshipped and 52% for the shipped semen.
Semen was not diluted with extender and not cooled for shipping
because staining properties of sperm with Hoechst 33342 are altered
by dilution with extenders. Furthermore, in other studies (see
Example 4), storing semen neat at ambient temperature between
collection and flow-sorting was found to be superior to diluting
it.
TABLE-US-00016 TABLE 16 Results of field trial 7 - Crossbred beef
heifers in Colorado, 1999 No. No. No. pregnant Treatment/site sperm
heifers day 33 to 37 Sexed, frozen/body 1.5 .times. 10.sup.6 86 34
(40%).sup.a Sexed, frozen/horns 1.5 .times. 10.sup.6 86 53
(62%).sup.b Control, 20 .times. 10.sup.6 35 .sup. 18 (51%).sup.a,b
frozen/body .sup.a,bMeans without common superscripts differ (P
< 0.01).
[0198] Field trial 8 (Table 17) concerned feedlot heifers not
implanted with growth promotants; at the time pregnancy was
diagnosed they were aborted, so calving data was not available.
This experiment illustrates that efficacious sexing also can be
done in the male direction. Pregnancy rates for the 2 bulls were 50
and 61%.
TABLE-US-00017 TABLE 17 Results of field trial 8 - Angus heifers in
Nebraska, 1999 No. No. No. pregnant.sup.a No. Treatment/site sperm
heifers day 74 to 76 fetuses Sexed, frozen 72 mW 1 .times. 10.sup.6
18 7 (39%) 6 (86%) laser/body Sexed, frozen, 135 mW 1 .times.
10.sup.6 18 13 (78%) 12 (92%) laser/body .sup.aNo significant
differences.
[0199] Field trial 9 (Table 18) was the only trial to show a
convincing advantage of 3.0 versus 1.5.times.10.sup.6 sexed, frozen
sperm/insemination dose. This advantage was true for both
inseminators. Pregnancy rates for sexed sperm from the 2 bulls were
62 and 75%.
TABLE-US-00018 TABLE 18 Results of field trial 9 - Red Angus
heifers in Nebraska, 1999 No. No. No. pregnant No. Treatment/site
sperm heifers day 60 to 63.sup.a fetuses Sexed, frozen/body 1.5
.times. 10.sup.6 15 8 (53%) 7 (88%) Sexed, frozen/body 3.0 .times.
10.sup.6 14 12 (86%) 9 (75%) Sexed, frozen/horns 1.5 .times.
10.sup.6 16 9 (56%) 7 (78%) Sexed, frozen/horns 3.0 .times.
10.sup.6 16 12 (75%) 11 (92%) Control, 20 .times. 10.sup.6 30 21
(70%) 13 (62%) frozen/body .sup.a3.0 .times. 10.sup.6 sexed sperm
had a higher pregnancy rate (80%) than 1.5 .times. 10.sup.6 sexed
sperm (55%), P < 0.05, 1-tail .chi..sup.2.
[0200] Pregnancy rates in field trial 10 (Table 19) with sexed,
frozen semen, were similar to controls; the accuracy of sexing
sperm on this trial was only 82%, which, however, is not
significantly different from the targeted 90% accuracy. Pregnancy
rates for sexed semen were 54, 66, and 50% for bulls AN4, AN7, and
AN8, respectively (P>0.1). Eighteen of the heifers inseminated
in this trial were the calves resulting from sexed sperm in field
trial 1.
TABLE-US-00019 TABLE 19 Results of field trial 10 - Angus heifers
in Wyoming, 1999 No. No. No. pregnant No. Treatment/site sperm
heifers day 61 to 63.sup.a fetuses Sexed, frozen/body .sup. 1
.times. 10.sup.6 44 26 (59%) 23 (85%) Sexed, frozen/body 3.0
.times. 10.sup.6 43 23 (53%) 17 (74%) Control, 20 .times. 10.sup.6
35 20 (57%) 12 (57%) frozen/body .sup.aNo significant
differences.
TABLE-US-00020 TABLE 20 Results of field trial 11 - Holstein
heifers in Colorado, 1999 No. No. No. pregnant No. pregnant
Treatment/site sperm heifers day 28 to 30.sup.a day 56 to
58.sup.a,b Sexed, frozen/body 1 .times. 10.sup.6 12 8 (67%) 7 (58%)
Sexed, frozen/body 3 .times. 10.sup.6 12 6 (50%) 4 (33%) Sexed,
frozen/horns 1 .times. 10.sup.6 7 4 (57%) 4 (57%) Sexed,
frozen/horns 3 .times. 10.sup.6 7 4 (57%) 4 (57%) Control, 20
.times. 10.sup.6 9 4 (44%) 3 (33%) frozen/body .sup.aNo significant
differences, .chi..sup.2. .sup.b16 of 17 (94%) fetuses from the
sexed semen treatments were female; 2 were too deep in the body
cavity to sex with ultrasound.
[0201] Data from trials were combined in which treatments were
identical except 1.times.10 and 1.5.times.10.sup.6 sperm doses were
pooled (Table 21).
TABLE-US-00021 TABLE 21 Meta-summary from combining trials with
sexed, frozen semen and frozen controls. Trials No. No. combined
Sperm no./site heifers pregnant 5, 6, 9, 11 1.0-1.5 .times.
10.sup.6/body 77 36 (47%) 3.0 .times. 10.sup.6/body 76 38 (50%)
1.0-1.5 .times. 10.sup.6/horns 72 32 (44%) 3.0 .times.
10.sup.6/horns 72 39 (54%) 20 .times. 10.sup.6/body, control 93 61
(66%) 4, 5, 6, 9, 1.0-1.5 .times. 10.sup.6/body 176 98 (56%) 10, 11
3.0 .times. 10.sup.6/body 171 88 (51%) 20 .times. 10.sup.6/body,
control 183 124 (68%) 5, 6, 7, 9, 11 1.5 .times. 10.sup.6/body 163
70 (43%) 1.5 .times. 10.sup.6/horn 158 85 (54%) 20 .times.
10.sup.6/body, control 128 79 (62%)
[0202] Pregnancy rates with sexed sperm were generally 70-90% of
unsexed controls within experiments with 7 to 20 times more sperm.
This difference was less in the more recent trials, possibly
reflecting improved sexing and sperm-processing procedures.
[0203] In some trials, heifers were examined for pregnancy by
ultrasound at both 1 and 2 months after insemination. Pregnancy
losses in this interval were similar (P>0.1) for sexed (23/261;
8.8%) versus control (9/145; 6.2%) sperm treatments, which is one
measure that genetic damage due to sexing is minimal. Calving
information was obtained from only a few of the pregnant heifers
because most cattle from the earlier trials were sold, and those
from later trials have not calved yet. The population of calves
produced to date from sexed semen appears to be no different from
the population of controls.
CONCLUSION
[0204] Sex ratios in cattle can be distorted to about 90% of either
sex by sorting sperm on the basis of DNA content with a flow
cytometer/cell sorter followed by cryopreservation and relatively
routine artificial insemination. Calves resulting from sexed sperm
appear to be normal. For most bulls in these studies, pregnancy
rates with 1.0 to 1.5.times.10.sup.6 sexed, frozen sperm were 70 to
90% of unsexed controls with 20 or 40.times.10.sup.6 frozen sperm
inseminated conventionally. These results apply to well-managed
heifers bred by well-trained inseminators using properly processed
semen. There may be a small advantage to inseminating sexed sperm
bilaterally into the uterine horns compared to standard uterine
body insemination.
[0205] The present invention has of necessity been discussed herein
by reference to certain specific methods and materials. It is to be
understood that the discussion of these specific methods and
materials in no way constitutes any limitation on the scope of the,
present invention, which extends to any and all alternative
materials and methods suitable for accomplishing the ends of the
present invention.
[0206] All patents and publications described are herein
incorporated by reference in their entirety.
* * * * *