What happens to all those sperm? :

The Interaction of Male and Female in
Success of Mating
R. G. Saacke, PhD
Dept. of Dairy Science, Virginia Tech, Blacksburg, VA

Introduction: To most in this audience, having a veterinary practice dealing with
problems associated with reproduction is undoubtedly fun, profitable and
rewarding. However, reproductive problems can also be most frustrating, often
testing the limits of our knowledge and our patience. From personal experience,
I can also say the same for research in reproductive physiology, particularly
where we are interested in understanding factors important to reproductive
success or identifying causes and remedies for reproductive failure. Since the
early 60s, in our lab we sought useful correlations of seminal traits and fertility in
order to ultimately predict the reproductive outcome of bovine semen used in
artificial breeding or the fertility of a specific male under natural service. Despite
these efforts, to this day we can only account for approximately 50% of the
variation in fertility among males by measuring seminal traits, leaving the goal of
predictability quite unachieved. In our frustration and need to progress in this
endeavor, shared by many other reproduction laboratories throughout the world,
the fate of sperm in the female reproductive tract (quantitatively and qualitatively)
has become an important question needing to be addressed. Answers in
response to this question have been enlightening and although they are not
"silver bullets" to predicting fertility, they have provided insight to the nature of
reproductive success and failure and have exposed the roots of some of our
frustrations. I would like to share some of these insights with you today.
Hopefully, they may explain some of the frustrations encountered in a therio
practice or perhaps offer solutions to the critical eye as new tools become
available in control of semen production as well as in the control of ovulation in
the female.

Selective Sperm Transport and Retention in the Female: Since the late 70s a
rich literature has developed addressing the fate of sperm in the female as well
as the influence of the female tract on the quality and quantity of sperm reaching
the site of fertilization. I would like to encapsulate the portions of this work most
meaningful to our current understanding of the female-male interaction,
particularly as it relates to the success or failure of an insemination. However,
for those interested in the area of sperm transport in the female per se, other
reviews should be consulted (Hawk, 1983: Hawk, 1987; Hunter and Wilmut, 1984
and Suarez et al. 1990, and for seminal quality aspects of sperm transport,
Saacke, 1982).
In cattle, Van Demark and Hays (1954) first reported the very rapid transport of
sperm from the site of deposition, naturally in the vagina or artificially in the
uterus, to the oviductal ampulla as between 2.5 and 3.3 minutes. Years later,
critical studies on the kinetics of sperm transport in the rabbit by Overstreet et al.
29
(1978) showed that sperm transport occurred in two phases, the rapid and
sustained. Indeed the first, rapid transport from the site of deposition to the site
of fertilization, did occur within 1-15 minutes post-coitus or insemination, but
these were primarily dead or moribund sperm that were passively ushered
through the tract by muscle contractions associated with coitus or insemination.
More importantly, there was an apparent build-up of sperm in the lower isthmus
of the oviduct which did not begin until approximately 4 hours post coitus,
reaching highest sperm numbers 10 to 16 hours post coitus (sustained sperm
transport). Drawn from this apparent oviductal sperm reservoir in the lower
isthmus, nearly 100% viable spermatozoa were found in the vicinity of the upper
isthmus and ampulla in proximity to ovulation (8-12 hours post-coitus), albeit in
relatively low numbers.
Thus, the colonization of the lower oviduct by a population of predominantly
viable spermatozoa during this sustained phase of transport is thought to provide
the potential fertilizing sperm that reach the site of fertilization at the ampullaryisthmic
junction of the oviduct. Timing of transport events would be expected to
vary among species. For example, in the bovine, colonization of the lower
isthmus by potential fertilizing sperm was found to occur over a period of 6 to 12
hours post mating (Hunter and Wilmut, 1984).
In the pig, Hunter (1984) provided evidence that the oviductal isthmus reservoir
most likely served to maintain spermatozoal function until ovulation. Using
mouse oviduct, which is translucent, Suarez (1987) observed the behavior of
mouse sperm in situ and in proximity to ovulation. Sperm were retained in the
isthmus by adherence of their heads to the mucosa as well as by an apparent
flagellar immobilization in this region. The adherence is mediated by sugar
residues in the cell membrane overlying the head region, fucose in the case of
bovine (Lefebvre et al., 1997). One line of evidence suggests that sperm in the
isthmic reservoir are released by cue(s), to continue progress through the site of
fertilization and the ampulla, from events associated with ovulation (for review,
Hunter, 1998) permitting timely union of sperm and egg. For a number of
species including mouse, rat, hamster, rabbit, sheep and cattle, Suarez et al.
(1990) reviewed the numbers of sperm in the oviductal isthmus and the oviductal
ampulla (near fertilization site) at the time of the impending ovulation. She also
included the variation among species in numbers of sperm deposited at mating.
Quite strong similarities were noted. Across species, the number of sperm
inseminated ranged from 50 million for the mouse to 3 billion for the bovine, while
numbers of sperm in the oviductal isthmus at the time of ovulation ranged from
4.4 thousand for sheep to 21.2 thousand for cattle, relatively small numbers
when compared to the inseminates. Found in the oviductal ampulla at ovulation
were only 2 sperm for the hamster and rat and 5, 10, 26 and 118 sperm for mice,
cattle, sheep and rabbits, respectively. The very small number of sperm passing
through the ampulla (site of fertilization) at any one time has been thought to be
an important natural safeguard against polyspermy (Hunter, 1988).
30

Where do the millions to billions of sperm inseminated go? There is evidence
that sperm are lost by simply passing through the reproductive tract into the body
cavity, through ingestion by phagocytes or by retrograde loss to the exterior
(Hafez, 1974). In a precise study of sperm loss in cattle following artificial
insemination directly into the uterus, nearly 90% of the sperm inseminated were
retrograded to the exterior or found in the vagina within 12 hours of insemination
(Mitchell et al. 1985). In sheep (Mattner, 1969), pigs (Pursel et al., 1978) and
cattle (Lineweaver et al., 1970) it has been shown that number of sperm reaching
the oviducts and retained in these organs is influenced downward by sperminjurious
events such as cryopreservation. Presumably, injured sperm are more
easily retrograded by the continuous caudal flow of female fluids or they are
removed by phagocytes. Nevertheless, sperm dosage in the inseminate has
been shown to be positively related to numbers of sperm accessing the oviduct in
rabbits (Morton and Glover, 1974) and ova in cattle (Nadir et al., 1993), making
losses from cryo-cell injury compensable by cell dosage. I believe that we can
say, that numbers of viable healthy sperm in the inseminate is important to the
number of sperm colonizing the oviductal isthmus reservoir under the sustained
transport system and is probably essential to the numbers or duration of sperm
progressing from this reservoir to the ampulla or engaging the ovum at the
ampullary-isthmic junction. There is not sufficient data available to speculate on
the nature of this relationship between inseminate numbers of sperm and
reservoir numbers of sperm. However, it would not be surprising if numbers of
viable sperm inseminated were positively associated with those available for
fertilization, but not in a linear fashion, rather a quadratic one with an asymptote.
It appears that, in vivo, protection against polyspermy appears to be a strong
priority in mammals.

Barriers in the Female Tract to Sperm Transport. Morphologically abnormal
sperm in semen of males has been associated with subfertility and sterility for
many years (Williams and Savage, 1925, 1927; Lagerlof, 1934). We now
recognize that sperm with classically misshapened heads, described by these
early workers using simple microscopes, do not traverse the female reproductive
tract or participate in fertilization based upon recovery and evaluation of
accessory sperm from ova and embryos (Saacke et al., 1998). Barriers
precluding their progression to the oviduct have been identified in a variety of
species. Barriers to abnormal tails and heads include, the cervix and cervical
mucus, in the bovine (Koeford-Johnson, 1972), rabbit (Mortimer, 1977) and
human (Barros et al., 1984); the UTJ and lower isthmus impair traverse by sperm
with abnormal heads in the mouse (Krzanowska, 1974, Nestor and Handel,
1984) and rabbit (Mortimer, 1977) and tails with droplets in the mouse (Nestor
and Handel, 1984). Considering the very small, intricate privedged paths offered
by the cervix and mucus of species having vaginal semen deposition (Mullins
and Saacke, 1989) as well as the intricacies of the UTJ in species having uterine
semen deposition (Hunter,1980), it may be that flagellar pattern is important to
sustained transport of sperm, removing cells with abnormal tails or protoplasmic
droplets. Similarly, Dresdner and Katz (1981) have shown that small geometrical
31
differences in head morphology can cause large differences in sperm
hydrodynamics. Thus, impaired or abnormal sperm motility may be the
underlying basis for sperm exclusion based upon head morphology as well. It
has also been observed that in vitro, sperm with abnormal heads in proximity to
the ovum were unable to attach to (Kot and Handel, 1987) or penetrate (Howard
et al., 1993) the vestments of the ovum. In felids, Howard et al., (1993) reported
that the zona pellucida itself provides a formidable barrier to abnormal heads with
the most abnormal being on the outer most portions of the zona and those with
improved morphology closest to the vitelline membrane. Spermatozoa with
abnormal acrosomes (were found to be impaired in their ability to attach to the
ovum in vitro and thus would not be thought to participate in fertilization;
however, their presence in an ejaculate apparently signifies incompetence in the
accompanying sperm of the ejaculate where embryonic development from
fertilized eggs is impaired (Thundathil et al. 2000). This apparently holds for
other sperm abnormalities as well, to the point that we are beginning to view
sperm abnormalities as the tip of an iceberg impairing reproductive efficiency.

From the Females point of View: When are Seminal Deficiencies Compensable:
Our current concepts are most clear from bovine data since artificial insemination
records are the most extensive for this specie. In this concept, the interaction of
the male and female was first depicted by Salisbury and VanDemark (1961)
showing that fertility increases with increasing numbers of quality sperm
delivered up to a threshold, after which, limiting factors in the reproductive
capacity of the female population become important. Pace et al. (1981) showed
this relationship to hold true for sperm viability traits of progressive motility,
acrosomal integrity, and cell membrane integrity. For each of these measurable
parameters, the number of sperm inseminated with the trait, not the percentage
having the trait, was related to fertility and in an asymptotic fashion. Thus,
seminal deficiencies resulting in subfertility due to below threshold numbers of
viable sperm delivered to the female would be considered compensable in that
adding sperm to the inseminate to above threshold numbers would eliminate the
subfertility. Sullivan and Elliott (1968) were the first to show that bulls differed in
the number of viable sperm necessary to reach the female threshold, thus
complicating the matter. They postulated that one cause of the difference in
threshold numbers among bulls was the abnormal sperm content of the semen.
This has been since validated by the fact that most abnormal sperm do not
access the ovum. However, in the bovine, males in artificial insemination can
differ 10 fold or more in ability to access the ovum in vivo based upon fertility
differences among bulls at low insemination dose (den Daas et al., 1998) or
based upon accessory sperm number differences among bulls measured at the
same insemination dose (Nadir et al., 1993). This strongly suggests that there
are compensable seminal deficiencies that cannot be explained by conventional
assessments of sperm viability or morphology. Most likely important to sperm
accessing the egg would be differences among bulls in molecular events on the
sperm surface or functional changes of sperm associated with colonizing and
storage in the lower oviductal isthmus under sustained sperm transport or such
32
events as ability to undergo capacitation, sperm/egg recognition or even the
acrosome reaction, all of which are still to be accurately quantified under
laboratory conditions. On that basis, we can say that we still have much to learn
before threshold sperm numbers in an inseminate or ejaculate can be calculated
or predicted for a given male. It then follows that maximum dilution rates in
artificial insemination or minimum inseminate dosages for our species of interest
are still not in hand except for obtaining adequate numbers of breedings that can
provide reliable fertility data to pinpoint the threshold.
From the Females point of View: When are Seminal Deficiencies

Uncompensable: Sullivan and Elliott (1968) also demonstrated that low fertility
males (at any dosage) generally required more sperm to reach their maximum
conception than did highly fertile males. Such low fertility males generally had
higher seminal content of abnormal cells. As stated earlier, this explains the
higher sperm dosage threshold or compensable component of the lower fertility
male. But, what about the uncompensable component of the low fertility male,
i.e. subfertility at any dosage? There is now good evidence that many sperm
with normal motility and morphology that are present in abnormal ejaculates are
able to access the egg, but not competent to complete fertilization or sustain
embryogenesis once these events are initiated (Barth, 1992; Courot and Colas,
1986; DeJarnette et al., 1992; Orgebin-Crist and Jahad, 1977; Setchell et al,
1988). Males having disturbances in spermatogenesis resulting in the
ejaculation of abnormal sperm usually provide a broad spectrum in severity of
morphological forms dependent upon the stage of spermatogenesis affected by
the disturbance (Vogler et al., 1991, 1993). Saacke et al. 1998 showed that
while classically abnormal sperm are indeed excluded from the ovum (accessory
sperm), sperm with normal or subtly misshapen heads in otherwise abnormal
ejaculates do gain access to the ovum. Which sperm are competent and which
are not is unclear; however, it is accepted that normal appearing sperm in
abnormal ejaculates are most likely the cause of the early embryonic death
associated with the male. Thus, abnormal sperm in ejaculates appear to signify
the "tip of the iceberg" with respect to uncompensable reproductive wastage
experienced by the use of such semen.
It should be recognized here that sperm with microscopically normal morphology,
but with defective chromatin have been implicated in cases of male subfertility for
some time (Gledhill, 1970). The chromatin structure assay developed by
Evenson et al., (1980) revealed a strong positive association between
heterospermic fertility and stability of sperm DNA to acid denaturation in bulls
(Ballachey et al., 1988). Acevedo et al., (2001) recently reported that
spermatogenic disturbances caused by elevated testicular temperature resulted
in the production of abnormal sperm and that vulnerability of sperm DNA to acid
denaturation was positively associated with abnormal shaped sperm, but also
extended to normal shaped sperm in the abnormal samples. This again, tends to
confirm that occurrence of morphologically abnormal sperm can signal chromatin
abnormalities and potential incompetence among both normal and abnormal
33
sperm in the same semen samples. It also underlines the fact that while female
sperm selection appears amazingly strong based upon sperm shape and motility,
it is far from absolute in excluding incompetent sperm from accessing the egg.

Natural Service vs Artificial Insemination and Timing of Mating in Relation to
Ovulation: Finally, a word or two should be said about the time of mating and the
nature of the mating, i.e., artificial vs natural service since both should subscribe
to our discussions above. In many species we know there is an optimum time of
mating, i.e., breeding too early or too late will result in depressed pregnancy
rates. In a recent study, using the 6 day-old bovine embryo as a bio-monitor for
optimum time of insemination, Dalton et al., (2001) examined insemination times
of: heat onset, 12 and 24 hours post onset. These times approximated 27 hours,
15 hours and 3 hours prior to the average ovulation time, respectively, which in
this case was approximately 27 ± 5 hours post onset of heat. Of interest from
this study was the nature of the loss due to early vs late insemination. Accessory
sperm recovered from the embryos/ova showed sperm accessibility to the egg
lowest when insemination was at heat onset and highest at insemination 24
hours post onset. As expected, fertilization rate followed in the same fashion low
at heat onset, highest at 24 hours. However, embryo quality was reversed, being
maximum at heat onset (greatest number of excellent embryos) and lowest
(highest number of degenerate embryos) at 24 hours post onset. Thus, the
insemination at 12 hours post onset would have provided the best pregnancy
rate; however, it was clearly a compromise between fertilization failure and
embryo failure. The early insemination provided sufficient time for sperm
transport and colonization of the oviductal isthmus, but lowered fertilization rates
were undoubtedly an outcome of the limitation of sperm life or retention in the
oviductal reservoir . On the contrary, the late insemination (24 hours post onset
of heat) had high fertilization rates from the expected high sperm accessibility
(accessory sperm number) but the embryo quality from this insemination was
impaired. Embryo quality may have suffered due to inadequate time for sperm
selection or the aging of ova in the oviduct awaiting sperm, since ovulation was
occurring at 22 to 32 hours post heat onset. With approximately a 6-hour
requirement for sustained sperm transport in the bovine, insemination at 24
hours post heat onset would not provide fertilizing sperm in the oviductal isthmus
until 30 hours or more post estrus resulting in the aging of ova as they await
arrival of sperm. These results were based upon the intrauterine artificial
insemination of a normal dose (25 million cells) of cryopreserved semen.
Dalton et al., 2001 also compared a single natural service at heat onset with
artificial insemination at heat onset and 12 hours post onset utilizing the same
bulls. For natural service an estimated 3 to 8 billion cells were deposited in the
vagina (cranial to the cervix) and for artificial insemination 25 million
cryopreserved sperm were deposited intrauterine (caudal to the cervix). The
natural service resulted in higher numbers of sperm accessing the egg, higher
fertility and higher embryo quality than did artificial insemination at either time.
The greater numbers of sperm from natural service and the lack of injury from
34
cryopreservation explain some of the differences; however, one is lead to wonder
what role the cervix might play in sperm selection in the bovine based upon the
improved embryo quality achieved by semen deposition caudal to the cervix.

Conclusions: Although we could not touch all the critical literature on this
interesting topic, clearly that which we did touch supports the concept that
understanding what happens to all those sperm and their fate in the fmale
addresses many of the male/female interactions important to reproductive
success or failure. It has also provided answers to some of our frustrations in
trying to predict the outcome of a mating or why our measures of reproductive
ability do not often track with results. Clearly, the sperm that reach the site of
fertilization are not the ones we evaluate in a BSE exam of a male. How far we
can breed an animal prior to ovulation or how close undoubtedly matters
depending upon the male, the uncompensable and compensable deficiencies in
his semen, semen preservation techniques and associated injury, how many
sperm are inseminated and what female barriers exist between sperm and egg,
i.e., site of deposition. Artificial insemination in many species, exotic,
endangered, recreational and food producing, continues to offer animal breeders
great potential from both genetic and health standpoints. However, we still have
much to learn from natural service with respect to sperm quality and quantity
available for fertilization as well as in the form of a basis for judging semen
preservation methods and other techniques. To close I would simply say, if I
were to remain active in my research career designed to improve artificial
insemination, gaining a better understanding of the events and concepts
associated with natural service would get most of my attention along with
continued efforts to understand the fate of sperm in the female tract.

References:
Acevedo, N., J. H. Bame, L. A. Kuehn, W. D. Hohenboken, D. P. Evenson, R. G.
Saacke. 2001. Effects of elevated testicular temperature on spermatozoal
morphology and chromatin stability to acid denaturation in the bovine. Biol
Reprod. 64 (suppl 1): 217-218.
Ballachey, B. E., D. P. Evenson, R. G. Saacke. 1988. The sperm chromatin
structure assay: relationship with alternate tests of semen quality and
heterospermic performance of bulls. J. Andrology 9:109-115.
Barth, A. D. 1992. The relationship between sperm abnormalities and fertility.
In: Proc 14th Tech. Conf. on Artif. Insemin. And Reprod., Nat'l, Assoc. Animal
Breeders, Columbia, MO. pp. 47-63.
Barros, C., P. Vigil, E. Herrera, B. Arguello, R. Walker. 1984. Selection of
morphologically abnormal sperm by human cervical mucus. Arch. Androl. 12
(suppl): 95-100.
Courot, M., G. Colas. 1986. The role of the male in embryonic mortality (cattle
and sheep). In: J. M. Greenan, M. G. Diskin (Editors), Embryonic Mortality in
Farm Animals. Dordrecht, Martinus Nijhoff, pp. 95-203.
Dalton, J. C., S. Nadir, J. H. Bame, M. Noftsinger, R. L. Nebel, R. G. Saacke.
2001. Effect of time of insemination on number of accessory sperm,
35
fertilization rate, and embryo quality in nonlactating dairy cattle. J. Dairy Sci.
84:2413-2418.
DeJarnette, J. M., R. G. Saacke, J. H. Bame, C. J. Vogler. 1992. Accessory
sperm: their importance to fertility and embryo quality, and attempts to alter
their numbers in artificially inseminated cattle. J. Anim. Sci. 70:484-491.
Den Daas, J. H. G., G. DeJong, L. Lansbergen, A. M. Van Wagtendonk-De
Leeuw. 1998. The relationship between the number of spermatozoa
inseminated and the reproductive efficiency of individual bulls. J. Dairy Sci.
81:1714-1723.
Dresdner, R. D., D. F. Katz. 1981. Relationship of mammalian sperm motility and
morphology to hydrodynamic aspects of cell function. Biol Reprod. 25: 920-
930.
Evenson, D. P., Z. Darznikiewicz, M. R. Melamed.1980. Relation of mammalian
sperm chromatin heterogeneity of fertility. Science 240:1131-1134.
Gleldhill, B. L. 1970. Enigma of spermatozoal DNA and male infertility: a review.
Am. J. Vet. Res. 31:539-549.
Hafez, E. S. E. 1974. Reproduction in Farm Animals. Pub. Lea and Febiger,
Philadelphia.
Hawk, H. W. 1983. Sperm survival and transport in the female reproductive tract.
J. Dairy Sci. 66: 2645-2660.
Hawk, H. W. 1987. Transport and fate of spermatozoa after insemination in
cattle. J. Dairy Sci. 70: 1487-1503.
Howard, J. G., A. M. Donoghue, L. A. Johnston, D. E. Wildt. 1993. Zona
pellucida filtration of structurally abnormal spermatozoa and reduced
fertilization in teratospermic cats. Biol. Reprod. 49:131-139.
Hunter, R. H. F. 1980. Physiology and Technology of Reproduction in the
Female. Pub. Academic Press, London. pp 122-127.
Hunter, R. H. F. 1988. Capacitation potential of the Fallopian tube: a study
involving surgical insemination and subsequent incidence of polyspermy.
Gamete Res. 21: 255-266.
Hunter, R. H. F. 1998. Sperm-epithelial interactions in the isthmus and ampulla
of the Fallopian tubes and their ovarian control. In: A. Lauria, F. Gandolfi, G.
Enne, L. Gianaroli (Editors), Gametes: Development and Function. Serono
Symp. Milano. pp. 355-367.
Hunter, R. H. F., I. Wilmut. 1984. Sperm transport in the cow: periovulatory
redistribution of viable cells within the oviduct. Reprod. Nutr. Develop.
24:597-603.
Koeford-Johnsen, H. H. 1972. Cervical secretions as a selective filter for
abnormal types of spermatozoa. Arsberetnig Inst. For Sterilitetsforskning,
Konelige Veterinaer-og Landbohojskole 15:171-176.
Kot, M. C., M. A. Handel. 1987. Binding of abnormal sperm to mouse egg zonae
pellucidae in vitro. Gamete Res. 18: 57-63.
Krzanowski, H. 1974. The passage of abnormal spermatozoa through the
uterotubal junction of the mouse. J. Reprod. Fertil. 38:81-90.
36
Lagerlof, N. 1934. Morphological studies on the changes in the sperm structure
and in the testes of bulls with decreased or abolished fertility. Acta Path.
Microbiol. Scand. 19:254-267.
Lefebvre, R., M.C. Lo, S. S. Suarez.1997. Bovine sperm binding to oviductal
epithelium involves fucose recognition. Biol. Reprod. 56:1198-1204.
Lineweaver, J. A., E. S. E. Hafez, M. H. Ehlers, W. M. Dickson and R. J. King.
1970. Sperm transport in cattle and gonadotropin-treated calves. Cornell Vet.
60: 372-376.
Mattner, P. E., K. W. Kentwistle and I. C. A. Martin. 1969. Passage, survival and
fertility of deep frozen ram semen in the genital tract of the ewe. Australian j.
Biol. Sci. 22: 181-188.
Mitchell, J. R., P. L. Senger, J. L. Rosenberger. 1985. Distribution and retention
of spermatozoa with acrosomal and nuclear abnormalities in the cow genital
tract. J. Anim. Sci. 61:956-963.
Mortimer, D. 1977. The survival and transport to the site of fertilization of diploid
rabbit spermatozoa. J. Reprod. Fertil. 51: 99-105.
Morton, D. B., J. D. Glover.1974. Sperm transport in the female rabbit: the effect
of inseminate volume and sperm density. J. Reprod. Fertil. 38:139-142.
Mullins, J., R. G. Saacke. 1989. Study of the functional anatomy of the bovine
cervical mucosa with special reference to mucus secretion and sperm
transport. The Anat. Record 225:106-117.
Nadir, S., R. G. Saacke, J. H. Bame, J. Mullins, S. Degelos. 1993. Effect of
freezing semen and dosage of sperm on number of acessory sperm, fertility
and embryo quality in artificially inseminated cattle. J. Anim. Sci. 71:199-204.
Nestor, A, M. A. Handel. 1984. The transport of morphologically abnormal sperm
in the female reproductive tract. Gamete Res. 10:119-126.
Orgebin-Crist, M., C. Jahad. 1977. Delayed cleavage of rabbit ova after
fertilization by young epididymal spermatozoa. Biol. Reprod. 16:358:363.
Overstreet, J. W., W. Cooper, D. F. Katz.1978. Sperm transport in the
reproductive tract of the female rabbit. II. The sustained phase of transport.
Biol. Reprod. 19:115-132.
Pace, M. M., J. J. Sullivan, F. I. Elliott, E. F. Graham, G. H. Coulter. 1981.
Effects of thawing temperature, number of spermatozoa and spermatozoal
quality on fertility of bovine spermatozoa packaged in 0.5-ml French straws.
J. Anim. Sci. 53:693-701.
Pursel, V. G., L. L. Schulman, L. A. Johnson. 1978. Distribution and morphology
of fresh and frozen-thawed sperm in the reproductive tract of gilts after
artificial insemination. Biol Reprod. 19: 69-73.
Saacke, R. G. 1982. Components of semen quality. J. Anim. Sci. 55 (Supp II); 1-
13.
Saacke, R. G., J. M. DeJarnette, J. H. Bame, D. S. Karabinus, S. Whitman.
1998a. Can spermatozoa with abnormal heads gain access to the ovum in
artificially inseminated super- and single-ovulating cattle? Theriogenology
51:117-128.
Salisbury, G. W., N. L. VanDemark. 1961. Physiology of Reproduction and
Artificial Insemination of Cattle. Pub. W. H. Freeman and Co., San Francisco.
37
Setchell, B. P., M. J. Occhio, M. S. Hall, M. S. Lourie, M. J. Tucker, J. L. Zupp.
1988. Is embryonic mortality increased in normal female rats mated to
subfertile males? J. Reprod. Fertil., 83:567-574.
Suarez, S. S. 1987. Sperm transport and motility in the mouse oviduct:
observations in situ. Biol Reprod. 36: 203-210.
Suarez. S. S., M. Drost, K. Redfern, W. Gottlieb. 1990. Sperm motility in the
oviduct. In: Fertilization in Mammals. Ed. B. Bavister, J. Cummins and E.
Roldan. Pub. Serono Symp. Nowell, Mass. USA. pp. 111-124.
Sullivan, J. J., F.I. Elliott.1968. Bull fertility as affected by an interaction between
motile spermatozoa concentration and fertility level in artificial insemination.
VI Int'l Cong. Anim. Reprod. Artif. Insem. 2:1307.
Thundathil, J. R. Meyer, A. T. Palasz, A. D. Barth, R. J. Mapletoft. 2000. Effect of
the knobbed acrosome defect in bovine sperm on IVF and embryo
production. Theriogenology 54: 921-934.
VanDemark, N. L., R. L. Hays. 1954. Rapid sperm transport in gthe cow. Fertil.
Steril. 5: 131-137.
Vogler, C. J., R. G. Saacke, J. H. Bame, J. M. DeJarnette, M. L. McGilliard.
1991. Effects of scrotal insulation on viability characteristics of cryopreserved
bovine semen. J. Dairy Sci. 74:3827-3835.
Vogler, C. J., J. H. Bame, J. M. DeJarnette, M. L. McGilliard, R. G. Saacke.
1993. Effects of elevated testicular temperature on morphology
characteristics of ejaculated spermatozoa in the bovine. Theriogenology
40:1207-1219.
Williams, W. W., A. Savage. 1925. Observations on the seminal micropathology
of bulls. Cornell Vet. 15:353-375.
Williams, W. W., A. Savage. 1927. Methods of determining the reproductive
health and fertility of bulls. A review with additional notes. Cornell Vet.
17:374-376.
38