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Topic:Fertility
Fertility in horses encompasses the physiological processes and factors influencing reproductive success in equine species. It involves the study of reproductive anatomy, endocrinology, and behavior, as well as the management practices that affect breeding outcomes. Key aspects include the estrous cycle, conception rates, and factors impacting stallion and mare fertility. Reproductive technologies such as artificial insemination, embryo transfer, and hormonal therapies are also explored to enhance breeding efficiency. This page compiles peer-reviewed research studies and scholarly articles that examine the biological mechanisms, management strategies, and technological advancements related to equine fertility.
Effects of semen fractionation and dilution ratio on equine spermatozoal motility parameters. Two experiments were conducted to examine the effects of semen fractionation and dilution ratio on motility parameters of stallion spermatozoa. In Experiment 1, three ejaculates from each of three stallions were divided into sperm-rich (SR) and sperm-poor (SP) fractions to determine the difference in sperm concentration. Mean sperm concentration in SR fractions (349.5 x 10(6)/ml) was greater (P < 0.001) than that of SP fractions (96.9 x 10(6)/ml). In Experiment 2, three ejaculates from each of two stallions were divided into SR and SP fractions. Fifty percent of the original volume of SR fract...
The ovulated ovum of the horse: cytology of nonfertilized ova to pronuclear stage ova. Fertilization and early development in the horse were studied by recovering oviductal ova at various times after postovulatory mating. Ova collected between 7 and 22 h post coitum (pc) were examined for evidence of fertilizing sperm, cellular changes accompanying fertilization, and pronuclear development. Five ova collected between 7 and 9 h pc contained a marginal metaphase plate, but had no indication of sperm components; three of these, however, showed reduced numbers of cortical granules. Two activated ova (10 and 14 h pc) were in telophase of the second meiotic division, following incorpo...
Induction and characterization of acrosome reaction in equine spermatozoa. Equine spermatozoa were incubated in a chemically defined medium for 8 hours. The medium preserved spermatozoal viability, as assessed by total spermatozoal motility, progressive spermatozoal motility, and spermatozoal exclusion of eosin stain. Effects of time and divalent cation ionophore, A23187, on the occurrence and character of the spermatozoal acrosome reaction were determined. Two light microscopic assays, a triple-stain technique and a chlortetracycline fluorescence assay, were calibrated with transmission electron microscopy for detection of the acrosome reaction. Incubation time and ...
Secretion rates and short-term patterns of gonadotrophin-releasing hormone, FSH and LH throughout the periovulatory period in the mare. We have developed a non-surgical technique for long-term collection of pituitary venous blood which consists of slightly diluted hypophysial portal blood into which pituitary hormones have been secreted. In these experiments jugular and pituitary venous blood samples were collected from five unmedicated, ambulatory mares at 5-min intervals for 2-6 h on 11 occasions during the 6 days surrounding the ovulatory LH peak. Jugular blood only was collected from another five periovulatory mares without pituitary cannulae. The duration of oestrus was similar in mares with and without pituitary cannulae...
Survival of equine embryos transferred to normal and subfertile mares. To test the hypothesis that an abnormal uterine environment was a cause of early embryonic loss in subfertile mares, morphologically normal embryos were transferred to normal mares (n = 20) and subfertile mares (n = 20), and embryo survival rates were compared. Embryos were recovered nonsurgically at Days 7 to 8 postovulation and transferred surgically to normal and subfertile mares that had ovulated on the same day or within 2 d after a donor. Survival of transferred embryos was monitored by ultrasonography of the recipient mare's uterus from Day 9 through Day 28 postovulation. There were no ...
The meiotic stage of preovulatory oocytes in mares. Confusion exists as to whether the oocytes of the domestic horse are ovulated at the first meiotic metaphase (MI) or the second (MII). In this study eight oocytes were collected from the preovulatory follicles of 16 mares 36 h after human chorionic gonadotropin CG treatment. Six of the eight oocytes were judged to be at MII by the presence of the first polar body and this judgement was confirmed by semithin sectioning in one. Of the two that had no polar body, one was found to be at MII after fixation for chromosomal analysis and the meiotic stage of the other remained undetermined. Since all ...
Ovarian disorders in domestic animals. The histologic appearance of the ovaries and persistence of corpora lutea vary considerably among domestic animals, particularly between spontaneous and induced ovulators. The seasonally polyestrous mare has a variety of unique characteristics in ovarian structure and general reproductive function. Among the anomalies of ovarian development is the bovine freemartin with gonads containing a mixture of male and female elements. A variety of ovarian cysts occur in domestic animals, and persistent corpora lutea with associated reproductive perturbations occur in several species. Ovarian tumors are...
Hormone therapy for control of reproduction in mares and stallions. Because the reproductive performance of mares is lower than that of any other domesticated species, hormone therapy is important in ensuring fertility and proper management of pregnancy. Current techniques of hormone therapy are discussed.
Role of progesterone in mobility, fixation, orientation, and survival of the equine embryonic vesicle. Luteal progesterone was removed by an injection of prostaglandin F2alpha or bilateral ovariectomy on Day 12 of pregnancy in pony mares. The embryonic vesicle remained mobile in the uterus until loss occurred on Days 13, 13, 15, or 19 in four prostaglandin-treated mares and Days 15, 17, 19, or 26 in four ovariectomized mares. Exogenous progesterone given daily, starting on Day 12, maintained pregnancy until Day 40 in five of five prostaglandin-treated and three of four ovariectomized mares. During two-hour mobility trials on Day 14, embryonic vesicles in mares without luteal or exogenous proges...
Motility and fertility of equine spermatozoa in a milk extender after 12 or 24 hours at 20 degrees C. The effects of extender and storage at 20 degrees C on equine spermatozoa were evaluated in two experiments using embryo recovery as the end point. In both experiments, inseminations were every other day, starting on Day 2 or 3 of estrus or after a 35-mm follicle was detected, with 250 x 10(6) progressively motile cells (based on initial evaluation). In Experiment 1, semen from two stallions was used to compare the motility and fertility of spermatozoa maintained in a) heated skim milk extender at 37 degrees C with insemination in <1 h; b) E-Z Mixin extender at 37 degrees C with inseminatio...
Effect of timing of progesterone administration on pregnancy rate after embryo transfer in ovariectomized mares. Ovariectomized recipient mares were divided into two groups. Group A mares received 300 mg progesterone in oil i.m. daily starting 5 days before transfer of a 7-day embryo. Group B mares received the same dose of progesterone, but starting at least 4 days before donor ovulation. Presence of an embryonic vesicle was determined by ultrasonography; mares were considered to be pregnant if they had normal vesicle development to Day 18. Pregnancy rates were: Group A, 6/8; Group B, 1/12 (P less than 0.01). An additional 4 mares in Group B had a vesicle visible at 14 days which degenerated or did not ...
Assessment of fertility and semen evaluations of stallions. (1) Various estimations of motility (subjective appreciation, count on video record, Doppler laser apparatus and optic-microcomputer analyser) or percentage of live spermatozoa (eosin-nigrosin staining) showed a higher repeatability for measurements of a same sample than for straws of a same ejaculate: the values were high (respectively greater than 0.78 and greater than 0.69) except for the optical analyser and staining. (2) Semen samples were collected from 80 stallions 5 times at 24-h intervals. The repeatability varied from 0.37 to 0.69 for gel-free volume, concentration, total sperm numbe...
Practicalities of insemination of mares with deep-frozen semen. From 341 stallions examined for sperm quality, 61% of warm-blooded stallions and 47% of cold-blooded stallions fulfilled the pre-existing criteria for their occasional use in insemination. From these stallions 51-71% of acceptable ejaculates were obtained. Altogether 959 mares were inseminated in an average of 1.36 oestrous cycles. For the insemination of one mare in one oestrous cycle on the average 2.2 insemination doses were used. These inseminations were carried out by 41 cattle insemination technicians trained in mare insemination. A pregnancy rate of 56% and a foaling rate of 48% were ac...
Effect of uterine inflammation and ultrasonically-detected uterine pathology on fertility in the mare. The incidence of intrauterine fluid collections during dioestrus (12/43, 28%) and uterine cysts throughout the oestrous cycle (11/73, 15%) found in this study indicates that these ultrasonically detectable abnormalities are prevalent in mares. The hypothesis that uterine cysts do not affect pregnancy was not supported. Intrauterine fluid collections at dioestrus represented the presence of an inflammatory process as indicated by a high biopsy score, reduced progesterone concentrations, and a shorter interovulatory interval. Mares with fluid collections at dioestrus had a lower pregnancy rate a...
Exogenous hormone regimens to utilize successfully mares in dioestrus (days 2-14 after ovulation) as embryo transfer recipients. Two hormone regimens were utilized for recipient mares which were 2-14 days after ovulation at the time of non-surgical embryo transfer. In Exp. I, 20 embryos were transferred non-surgically into recipient mares which had been given 22 mg altrenogest daily starting the day of recipient ovulation. Higher (P less than 0.05) pregnancy rates (50% vs 0%) were obtained in mares which were 2-6 days after ovulation at the time of transfer compared with mares which were 7-12 days after ovulation. In Exp. II, on the day the donor mare ovulated (Day 0), 10 mg PGF-2 alpha were given to the recipient mare ...
Alternative solutions to hCG induction of ovulation in the mare. Injection of hCG (2000-2500 i.u., i.v.) to mares when a follicle reaches 35 mm induces ovulation between 24 and 48 h. However, repeated injections induce antibodies against hCG. We report attempts to induce ovulation without this inconvenience. We called 'response' an ovulation between 24 and 48 h after treatment. The typical response to hCG was obtained in 73% (N = 145) of treated mares. After immunization against hCG, the response (0%, N = 10) was less than in nonimmunized controls (100%, N = 9). Simultaneous injection of dexamethasone and hCG resulted in induction of ovulation (71%, N = 14)...
Influence of follicular status on twinning rate in mares. Between 1982 and 1985, 1015 mares were evaluated using the following parameters: age, mare status (maiden, barren, lactating), Caslick index, Caslick operation, ovarian cycle, ovarian and follicular size, treatments (hCG and intrauterine infusions), number of ovulations after mating (184 mares), number of conceptuses present, dimensions of embryonic vesicles, and pregnancy status 45 days after mating. Mares were examined ultrasonographically between Days 12 and 25 to detect the presence of embryonic vesicles and measure the dimensions of each vesicle. The data were analysed by a stepwise logis...
An update of chromosomal abnormalities in mares. Chromosomal abnormality was detectable in 98 of 180 mares aged 3 years or over with gonadal dysgenesis. The most common abnormality was X monosomy (63,X). The second most common abnormality was a karyotype indistinguishable by G- or C-banding from that of a male horse (64,XY). Two mares demonstrated structural abnormality of one X chromosome [64,X,del(Xp)] which has not previously been reported in horses. One of these foaled a filly with the same karyotype as her dam. Blood typing confirmed parentage of the foal. This is the only example in our experience of fertility in a mare with gonadal dy...
Extraspecific donkey-in-horse pregnancy as a model of early fetal death. Transfer of donkey embryos to horse mares provides a useful model of early fetal death. Endometrial cups do not develop in this one type of extraspecific pregnancy and 80% of donkey fetuses are aborted between Days 80 and 100 of gestation in conjunction with abnormal implantation and an intense accumulation of leucocytes in the endometrium of the surrogate mare. Treatment of mares carrying donkey conceptuses with progestagen (allyl trenbolone) or purified horse chorionic gonadotrophin does not prevent abortion. However, passive immunization with serum from mares carrying intraspecific horse fe...
Evaluation of mare oocyte collection methods and stallion sperm penetration of zona-free hamster ova. Comparisons were made between 2 methods of oocyte recovery from the ovarian follicles of slaughtered mares: 500 oocytes (3 per mare) were obtained by aspiration of follicular fluid from ovaries of 162 mares, and 120 oocytes (8 per mare) by isolation and rupture of follicles from ovaries of 14 mares. In the oocytes recovered after rupture of follicles, 89.2% were morphologically unchanged, in comparison to 29.3% obtained by aspiration of follicular fluid. Stallion spermatozoa capacitated in vitro were tested on zona-free hamster oocytes. The stallion spermatozoa were washed in TCM-199 and prein...
Early pregnancy loss in brood mares. During 1985, linear-array ultrasonography was used to study early pregnancy loss in commercial brood mares: 600/1115 (54%) of the cycles resulted in detected pregnancy at Week 2 after ovulation and 80 (13%) of these pregnancies resulted in early pregnancy loss. The pregnancy loss rate was significantly higher (P less than 0.05) for twin pregnancies (10/41) than for singleton pregnancies (70/559). The pregnancy loss rate was significantly higher (P less than 0.05) at 2-4 weeks (29/60) than at 6-8 weeks (12/60). The pregnancy rate was significantly less (P less than 0.05) for post-partum mares i...
Infusion of gonadotrophin-releasing hormone (GnRH) induces ovulation and fertile oestrus in mares during seasonal anoestrus. In Exp. 1, 30 Standardbred mares in deep seasonal anoestrus were divided into 3 equal groups and treated with 0, 50 (G50) or 100 (G100) ng GnRH kg-1h-1 for 28 days via osmotic minipumps. Ovulation occurred in 0/10, 3/10 and 7/10 mares respectively (P less than 0.05). Plasma GnRH profiles (Days -6, 0, 2, 6, 12, 20, 28 and 34 relative to pump insertion) were dose-dependent (P less than 0.01) and peaked on Day 12 of infusion. Mean daily plasma LH concentrations were biphasic in treated mares that ovulated, with LH peaks occurring around Day 6 and Days 16-20. By contrast, in treated mares that did...
Induction of ovulation in anoestrous mares with a slow-release implant of a GnRH analogue (ICI 118 630). A total of 18 experimental pony and 136 commercial maiden, barren and foaling Thoroughbred mares in seasonal or lactation-related anoestrus were injected subcutaneously with 1 or 2 slow-release D,L-lactide-glycolide co-polymer implants impregnated with 0.9 or 1.8 mg of the potent GnRH analogue, ICI 118 630, to give a daily release of, respectively, 30 or 60 micrograms analogue for 28 days; 32 of the Thoroughbred mares were also given a daily oral dose of 27.5 mg allyl trenbolone for 5 days after injection of the implant. Thirteen pony (76%) and 120 Thoroughbred (88%) mares ovulated 3-18 days a...
Proteins in stallion seminal plasma. Motility and fertility of frozen-thawed semen differs greatly amongst stallions. Differences in seminal plasma might be one cause of this variation. For 8 ejaculates from each of 17 stallions, seminal plasma was saved at -20 degrees C and spermatozoa were cryopreserved. Based on post-thaw sperm motility, seminal plasma samples from 7 stallions (2 good, 3 variable, 2 poor sperm motility) were selected for measurement of electrolytes, protein content and analysis by sodium dodecylsulphate gel electrophoresis (10% gel, Coomassie blue stain). Variation in seminal plasma was significant (P less tha...
Fertility of pasture bred mares in synchronized oestrus. Oestrus was synchronized in 220, 300 and 272 mares in 1983, 1984 and 1985 respectively. Mares were given two injections of 250 micrograms fenprostalene 15 days apart except in 1983 and 1984 when 56 and 53 of the synchronized mares were given 1-10 daily injections of 150 mg progesterone and 10 mg oestradiol-17 beta to delay and synchronize post-partum oestrus. At 2 days after the second PG injection or 7 days after the last progesterone + oestradiol treatment, mares were divided into groups of 15-21, and each group was placed in a separate pasture with a stallion for 7 weeks. Pregnancy rates we...
Influence of season and frequency of ejaculation on production of stallion semen for freezing. In an attempt to define optimal season and ejaculation frequency for frozen semen, semen was collected from 6 stallions (3 horses and 3 ponies) 3 times per week or every day, alternating every week, for 1 year. The semen was evaluated and frozen. All the samples were thawed at the end of the experiment. At collection, fresh semen evaluations showed that winter (as opposed to spring and summer) was associated with low sexual behaviour, small volumes of spermatozoa and gel, high sperm concentration and lower motility. The high ejaculation frequency yielded a decreased volume, concentration of sp...
