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Topic:Reproduction
Reproduction in horses encompasses the biological processes and mechanisms involved in the breeding and development of equine offspring. This includes the study of reproductive anatomy, physiology, and endocrinology in both mares and stallions. Key areas of interest include the estrous cycle, ovulation, conception, gestation, and parturition. Researchers also examine factors influencing fertility, reproductive technologies such as artificial insemination and embryo transfer, and management practices that impact reproductive success. This page compiles peer-reviewed research studies and scholarly articles that explore the physiological, genetic, and environmental aspects of equine reproduction.
Factors affecting uterine clearance of inoculated materials in mares. Twelve acyclic mares of various ages (2-29 years) and parity (maiden-multiparous) were given oestradiol-17 beta i.m. (winter 1982) or progesterone i.m. (winter 1983) to induce changes in the endometrium consistent with oestrus and dioestrus, respectively. After hormone treatment, mares were inoculated intrauterine with 50 ml saline containing 5 X 10(5) Streptococcus zooepidemicus bacteria, 51Cr-labelled 15-micron microspheres, and 500 mg charcoal (Groups E + B and P + B) or microspheres and charcoal only (Groups EC and PC). At 5 h after inoculation uteri were flushed with 50 ml saline containi...
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...
Prolactin response to thyrotrophin-releasing hormone stimulation in normal and agalactic mares. Serum prolactin concentration was determined before and after TRH administration to normal mares at 10 months of gestation, 2 and 4 months post partum and during a -7- to +14-day peri-parturient period. The serum prolactin concentration increased significantly (P less than 0.05) at 15, 30 and 60 min after TRH administration in the normal mares regardless of the season of the year, pregnancy or lactation status. However, during the periparturient period, the basal prolactin concentration was increased 4-fold and there was only a marginal increase after TRH administration. Of 9 agalactic mares, ...
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 ...
Use of push-pull perfusion techniques in studies of gonadotrophin-releasing hormone secretion in mares. Push-pull perfusion was used to study GnRH secretory ability of the hypothalamus in anoestrous, transitional, dioestrous and oestrous Pony mares. The technique involved placement of a concentric (tube within a tube) cannula into the area of the medial basal hypothalamus and perfusing a carrier medium (artificial cerebrospinal fluid) through the inner tube whilst aspirating from the outer tube so that the flow rate within the hypothalamic tissue was essentially constant. The perfusion rate was 0.5 ml/10 min and samples were collected at 10-min intervals for 10-15 h. The carrier medium, which co...
Changes in maternal hormone concentrations associated with induction of fetal death at day 45 of gestation in mares. Pregnant Standardbred mares were allocated to 2 groups. On Day 45 of gestation, 20-45 ml saline (240 g NaCl/l) were injected into the fetal sacs of 10 mares, and the other 10 mares were given sham treatment. Post-operative plasma oestrone sulphate concentrations were lower (P less than 0.01) on Days 48-55 in saline-treated mares than in sham-treated mares. Mean plasma progesterone profiles were similar in the two groups of mares, although post-operative luteolysis occurred in 4 saline-treated mares. There was no difference in plasma CG profiles between the 2 groups, except that CG concentratio...
Circadian, circhoral and seasonal variation in patterns of gonadotrophin secretion in geldings. Blood samples were obtained from 5 mixed-breed, long-term castrated geldings during five 24-h periods between May 1984 and April 1985. Blood samples were collected, beginning at 09:00 h, at 15-min intervals for 8 h and hourly for the remaining 16 h. Plasma concentrations of LH and FSH were determined by RIA. Seasonal changes in hormone concentrations and frequency and amplitude of secretory pulses were evaluated. No diurnal variation in either LH or FSH secretion was observed: however, marked circhoral fluctuations in LH and FSH secretion were noted. Mean LH and FSH concentrations in these lon...
Analysis of the physiological processes connected with sexual maturation of stallions. Physiological processes connected with sexual maturation of stallions were observed on 10 half-breed Anglo-Arab stallions beginning from 8 months of age, until 4.5 years of age. It was found that there is full somatic and sexual development in the stallion reached around the age of 3.5 years, and the sperm morphology stabilized in the range of the physiological norm around 3.0 years of age. On the other hand biochemical components of the semen plasma such as glycerylphosphorylcholine (GPC), ergothioneine (EGT), total protein (PRT), up to age 4.5 years, reach significantly lower value than in m...
The effects of four levels of endophyte-infected fescue seed in the diet of pregnant pony mares. Mean weight of 20 Quarter Horse placentas on a wet basis was 3.27 +/- 0.17 kg. These placentas contained mean dry fat-free tissue, DNA, RNA and collagen weights of 411 +/- 24 g, 11.2 +/- 0.6 g, 12.4 +/- 0.7 g and 210 +/- 15 g, respectively. In Ponies and Quarter Horses, there was a trend towards a decrease in these 4 values as gestation length increased. Analysis of placentas of Ponies fed different amounts of endophyte fungus-infected fescue seed showed that weight of dry fat-free tissue increased with increasing percentages of fescue seed in the diet. Diets containing fescue seed resulted in...
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)...
The carrier state in equine arteritis virus infection in the stallion with specific emphasis on the venereal mode of virus transmission. The carrier state has been confirmed virologically in Thoroughbred and non-Thoroughbred stallions naturally infected with equine arteritis virus (EAV). Short-term or convalescent and long-term carriers occur. The frequency rate of the long-term carrier state in Thoroughbreds was high, averaging 33.9% among the three groups of stallions under study. While the convalescent carrier state only lasted a few weeks after clinical recovery, the long-term carrier state could persist for years. There was evidence, however, that not all such carriers might remain persistently infected for life. Carrier s...
Analysis of X-chromosome inactivation in horse embryos. To define the time of X-chromosome inactivation in the horse, 122 conceptuses were collected transcervically between Days 6 and 28 (ovulation = Day 0) and subjected to cytogenetic analysis: 59 of the embryos were divided and in 41 of these separate cytogenetic analysis of the embryonic disc and remaining tissues was possible. Conceptuses were measured and photographed before capsule removal, culture in the presence of 5-bromodeoxyuridine and subsequent fixation for cytogenetic analysis. On average, 15 slides were prepared per conceptus. C-banding was used to determine the sex of each conceptus...
Fatty acid composition of the plasma lipids of the maternal and newborn horse. The fatty acid composition of the plasma free fatty acid, triacylglycerol and phospholipid fractions was measured in blood and milk samples taken daily from 3 mares and their foals on Days 1-9 post partum inclusive, and from a total of 12 mares and foals on Days 22, 30 and 51. A rise in the plasma concentrations of triacylglycerol and phospholipid similar to that well documented in other species occurred in the neonatal period. Alterations in the composition of the foal plasma phospholipid after birth lend support to the view that the placenta rather than the fetus could be responsible for the...
Inhibition of ovulation in the mare by active immunization against LHRH. To investigate the hypothesis that the onset of the breeding season in the mare may be due to a daylength-induced seasonal increase in LHRH pulse frequency, 5 mares were immunized against LHRH. Beginning 1 December, 5 immunized and 5 untreated control mares were exposed to an abrupt, artificial increase in daylength (16L:8D) to advance the onset of the breeding season. In control mares ovulation occurred 49.6 +/- 3.5 (s.e.m.) days later (18 January), whereas in 3/5 immunized mares ovulation had not occurred by 1 April. In the remaining 2 mares, although ovulation occurred once (Mare 79) or twi...
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...
Antepartum evaluations of the equine fetus. Measurements were made by real-time ultrasonography in 14 healthy mares to assess fetal growth and estimate newborn foal weights. Intrauterine fluid volumes were estimated and the placenta was measured and observed for maturational changes. The onset and incidence of echogenic particles in the allantoic fluid were recorded. In the second approach, baseline fetal heart rate, physiological rate variations and number, amplitude and duration of recorded accelerations were measured. Estimates of birth weights were within +/- 3.49 kg. Allantoic fluid was evident in all sonographic planes within the ...
Ultrasonography of accessory sex glands in the stallion. The accessory sex glands of 10 stallions were examined by transrectal ultrasonography. Seminal vesicles were 26.4 +/- 5.2 (s.d.) mm in width and 9.2 +/- 3.1 mm in height. Ampullae were 16.3 +/- 3.6 mm in width and 12.9 +/- 3.9 mm in height. Bulbourethral glands were 19.7 +/- 4.6 mm in width and 32.4 +/- 6.7 mm in length. Prostate lobes exceeded 34 mm in width and were 23.5 +/- 5.7 mm in height. The prostatic isthmus was 6.0 +/- 1.4 mm in height. The seminal colliculus, masculine uterus, and deferent ducts were also identified and characterized. Five of these stallions were killed to compare tr...
Investigation into the heredity of congenital lateral patellar (sub)luxation in the Shetland pony. A breeding experiment was carried out in a group of Shetland ponies in order to investigate the heredity of congenital lateral patellar (sub)luxation. A breeding herd was established and consisted of stallions and mares acquired at different times. Some were free from, and others were affected by lateral patellar (sub)luxation in either one or both femoropatellar joints. Over a period of 20 years, 49 foals were born from different mating combinations. Some offspring were free from the defect and others showed the abnormality. Though the number of foals bred during the experiment is rather smal...
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...
PGF-2 alpha release, progesterone secretion and conceptus growth associated with successful and unsuccessful transcervical embryo transfer and reinsertion in the mare. The outcome of 23 collections and reinsertions of conceptuses on Days 10.5-13.5, 4 transfers of Day-10.5, and 13 transfers of Day-6.5 embryos (ovulation = Day 0) was monitored in 30 mares. Blood samples were taken before and after each procedure to measure plasma 15-keto-13,14-dihydroprostaglandin F-2 alpha (PGFM), and then daily for progesterone determinations. Mares were also subjected to daily teasing for detection of oestrus, and to uterine ultrasonography for tracing the development of the conceptus. After the reinsertions, 12/23 conceptuses were detectable immediately after the procedure...
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...
Comparison of progesterone and progesterone + oestrogen on total and specific uterine proteins in pony mares. Eight ovariectomized pony mares were used to test the effect of various doses of progesterone (0, 50, 150, 450 mg/day, in oil, i.m., for 10 days) on progesterone and LH in the peripheral circulation, and on total protein and uteroferrin in uterine secretions. Progesterone increased uteroferrin, but there were no differences amongst doses of progesterone. Progesterone treatment decreased LH, and tended to increase total protein. Eighteen ovariectomized mares were given vehicle, oestradiol (10 mg/day, in oil, i.m.), progesterone or progesterone + oestradiol for 28 days. Both the last two steroid...
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...
Expression of major histocompatibility complex (MHC) antigens on horse trophoblast. Antibodies to fetal major histocompatibility complex (MHC) antigens are routinely detected in the serum of pregnant mares some 2-4 weeks after formation of the endometrial cups at Day 36-38 after ovulation. Several experimental approaches were taken to determine whether paternal MHC antigens are expressed on horse placental tissues. First, absorption of anti-paternal MHC antisera with a large volume of endometrial cup cells removed antibody activity in only 2 of 4 experiments. Second, repeated immunization of horses with endometrial cup tissue recovered from a mare on Day 47 of pregnancy faile...
Application of recombinant DNA techniques to structure-function studies of equine protein hormones. Complementary (c)DNA libraries have been made from horse pituitary gland and endometrial cup tissues with the aim of isolating the genes for the horse gonadotrophins (FSH, LH and CG) and growth hormone (GH). Southern (DNA) and Northern (RNA) blotting techniques were used to demonstrate that several heterologous (human and ovine) cDNA probes would be adequate for isolating the horse genes. A human cDNA probe was then used to isolate the horse gonadotrophin alpha-subunit cDNA from the pituitary and endometrial cup libraries. The nucleotide sequences from both tissue sources were identical, there...
Fine structure of the follicular oocyte of the horse. Oocytes recovered by follicular aspiration were evaluated by light and transmission electron microscopy. Of the 22 oocytes, 4 exhibited characteristics of degeneration, and the remaining 18 were in various stages of meiotic development. Of the non-degenerate oocytes, 14 were in the germinal vesicle stage, 2 had undergone nuclear membrane disintegration, 1 displayed chromosomes in late metaphase I-early anaphase I, and 1 oocyte was in the process of extrusion of the first polar body. Although some oocytes retained complete cumulus cell investments, oocytes were predominantly enclosed only by th...
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...
