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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.
Ultrastructure of cryopreserved horse embryos. Embryos were recovered non-surgically at about Day 6 after ovulation from 15 Quarter horse-type mares and were evaluated for morphological changes which may occur because of exposure to the cryoprotectant and/or cryopreservation. Electron microscopy was used to elucidate the fine structure of intracellular organelles which, if damaged, could cause cellular death. The horse embryo does not totally re-expand in the 10% glycerol freezing medium, nor will it completely re-expand in the isotonic holding medium following glycerol removal whether or not the embryo has been frozen. Embryos in this stu...
Changes in thecal and granulosa cell LH and FSH receptor content associated with follicular fluid and peripheral plasma gonadotrophin and steroid hormone concentrations in preovulatory follicles of mares. Individual antral follicles from 11 horse mares were studied at three stages of the oestrous cycle to determine the characteristics of the presumptive ovulatory follicle. Mares were ovariectomized (ovex) during the late luteal phase on Day 14 after ovulation (Group 1) and on the 1st (Group 2) or 4th (Group 3) day of oestrus. Every follicle greater than 5 mm in diameter was dissected from each ovary; follicles greater than or equal to 15 mm in diameter were analysed separately while others were pooled by size for subsequent analyses. The presumptive ovulatory follicle possessed the following ch...
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...
Relationship of age and season and consumption of Senecio vulgaris to LH/hCG receptors in the stallion testis. Testes were obtained from 70 colts and stallions and were pooled according to age (4 months to 23 years) to determine the relationship of age to LH/hCG receptor kinetics. The receptor concentration (Rt) increased from 0.069 x 10(-11) M/mg crude membrane fraction (CMF) for the 4-14-month pools to 0.464 x 10(-11) M for the 2-3-year-old pools. A 10-fold increase in testicular size also occurred, and so the total number of receptors per testis was significantly increased. A further increase to 1.237 x 10(-11) M/mg CMF was observed for stallions older than 5 years. No differences in binding affinit...
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...
Molecular genetic analysis of the major histocompatibility complex in an ELA typed horse family. Restriction fragment length polymorphism was studied in an ELA typed horse family which included a stallion, a mare with two full-sibs, another mare with three full-sibs and, in addition, three paternal half-sibs. DNA samples from all individuals were investigated by Southern blot analysis using three restriction enzymes (EcoRI, HindIII or TaqI) and human cDNA class I, class II (DR beta) and class III (C4) probes. In addition, a genomic class II DQ alpha probe was used. Fragments hybridized with the various probes revealed the existence of DNA sequences homologous to HLA class I, DR beta, DQ a...
Equilin and equilenin biosynthesis. Stereochemistry of aromatization of 3-hydroxy-3,5,7-androstatrien-17-one by horse placenta. The metabolic pathway leading to equilin and equilenin biosynthesis in the pregnant mare is different from that of estrone and estradiol and it is apparently cholesterol-independent. The precise precursors and intermediates and the stereomechanism of equine placental aromatization have not been established. [1,2-3H, 4-14C]3-Hydroxy-3,5,7-androstatrien-17-one was synthesized as a potential substrate and the 3H-distribution was analyzed by biochemical and chemical derivatization methods. The substrate was converted to equilin, equilenin and Heard's ketone by horse placental microsomes with a sp....
Genetic and temporal variation in serum concentrations and biological activity of horse chorionic gonadotrophin. The variation in the quantity of circulating chorionic gonadotrophin (CG) and its follicle-stimulating hormone (FSH) and luteinizing hormone (LH) activity in rodent bioassay systems was investigated. A portion of the variability in total CG could be attributed to the stallion that sired the pregnancy and it was possible to select sires and mares to increase CG production. It was further demonstrated that FSH activity per unit of CG was greater at Days 71 and 104 of gestation than at Day 39. LH activity per unit of CG varied with the sire, but no effect of day of gestation could be shown. It wa...
[Endometrial cysts in the mare. 2. Clinical studies: occurrence and significance]. Endometrial cysts were found in 11 (13.4%) of 82 mares of various breeds by clinical examinations. Endometrial cysts were diagnosed by hysteroscopy and ultrasonic echography. Typical images are described. The importance of endometrial cysts is discussed with regard to differential diagnosis of early pregnancy and uterine pathology. There was no evidence of cysts in mares under 10 years of age. Mares with endometrial cysts had a 10% higher history of disturbed fertility than mares without endometrial cysts. Seven of nine mares with cystic structures in the uterus became pregnant. Endometrial cy...
Influence of chlorhexidine on seminal patterns in stallions. Ejaculates were collected at 3-day intervals before, during and after a washing procedure with chlorhexidine (2%). Semen motility and pathology were determined before and after deep-freezing. Blood samples were taken before and within 1 h after washing procedures and then extracted in ether. This was followed by HPL chromatography. Chlorhexidine concentrations in blood and seminal plasma were distinctly higher in the treated stallions than in control groups. Concentrations in the control groups were below the detection limit of the column. Significant correlations between decreasing semen qual...
Release of LH, FSH and GnRH into pituitary venous blood in mares treated with a PGF analogue, luprostiol, during the transition period. Nine mares received cannulae to collect blood from the pituitary venous outflow in the intercavernous sinus (ICS) and the jugular vein; in 4 mares, only jugular cannulae were used. Those 4 mares and 3 of the mares with cannulae in both positions received 7.5 mg luprostiol i.m. and 1 mare with both cannulae was treated with 3.75 mg uprostiol i.v. Blood samples were kept before and after treatment at 2-, 5- or 10-min intervals and concentrations of LH, FSH and GnRH were determined by RIA. Treatments resulted in an immediate sharp rise of LH and FSH in ICS and jugular blood samples within 2-10 mi...
Patterns of oxytocin secretion during the oestrous cycle of the mare. From a group of 11 cyclic mares, blood samples were collected at 3-min intervals for 2 h and at 15-min intervals for an additional 6 h during four stages of the oestrous cycle. Mean plasma oxytocin concentrations (pg/ml, LSM +/- se) were greater on Day 15 after ovulation (169.9 +/- 17.6) than on Day 0 (82.6 +/- 17.6; P less than 0.01), Day 3 (97.2 +/- 20.4, P less than 0.01) and Day 7 after ovulation (104.0 +/- 25.0, P less than 0.05). Oxytocin was secreted in a pulsatile manner throughout the oestrous cycle, with short (0-29 min), medium (30-89 min) and long (greater than 90 min) duration rhy...
Effect of pulsatile gonadotrophin release on mean serum LH and FSH in peri-parturient mares. Changes in the pattern of LH and FSH in serum were studied in 6 mares foaling during the summer. Samples were collected frequently (every 15 min) for 24 h twice before foaling, -33 +/- 2 and -12 +/- 2 days, and for 12 h after foaling, on Day 0 and Day 4. Simultaneous pulses of FSH and LH were observed before foaling (r2 = 0.99). Before foaling, gonadotrophin pulses were infrequent (6 in 264 h of observation). On the day of foaling, LH and FSH pulse frequency increased (P less than 0.005) with 2-4 pulses per mare. The amplitudes of pulses of LH and FSH were higher before parturition than for th...
Comparison by three different radioimmunoassay systems of the polymorphism of plasma FSH in mares in various reproductive states. FSH was measured in the pituitary, and in pituitary venous and jugular blood collected at frequent intervals from mares in various reproductive states, using 3 validated and highly specific radioimmunoassay systems based on different antibodies, 'o', 'h' and 'e'. In the pituitary, 4 forms of FSH were found which differed in isoelectric point and relative potency in the 3 assays. In jugular blood, mean FSH concentrations and short-term patterns depended on the assay used and the reproductive state of the mare. In pituitary venous blood, although FSH concentrations were greatly elevated above ju...
Effect of altrenogest on pregnancy maintenance in unsynchronized equine embryo recipients. Non-surgical embryo recovery attempts were done on Day 7 after ovulation. Embryo recovery rate from mares of varied reproductive histories was 57% (38/67). Non-surgical transfer of these embryos into altrenogest-treated recipient mares that ovulated between 3 days before and 3 days after the donor resulted in a 30-day pregnancy rate of 77% (10/13). Transfer of embryos into altrenogest-treated recipients that ovulated between 4 days before and 6 days after the donor resulted in an overall pregnancy rate of 64% (16/25) at Day 30 of gestation. No recipients that were in oestrus at the start of tr...
Transitory changes of hormones in the plasma of parturient pony mares. Frequent blood samples were collected from 8 pony mares before, during and after labour, parturition and placental expulsion and assayed for progesterone, oestradiol, androstenedione and LH concentrations by radioimmunoassay. A significant (P less than 0.05) decrease in progesterone, oestradiol and in the progesterone:oestradiol ratio was not detected until 0.5 h after foaling. Androstenedione concentrations rose before and peaked at parturition and then declined. A significant (P less than 0.05) rise in LH was detected 0.5 h after parturition. This LH peak was not detected in one mare and she...
Equine half sibs with an unbalanced X;15 translocation or trisomy 28. Two unrelated chromosome abnormalities were found in equine half sibs. The proposita, Case 1, which was short in stature and infertile, had a de novo unbalanced X;15 translocation involving loss of Xp. Replication studies indicated that the translocated X was preferentially late replicating and that this late replication spread variably into the autosomal segment. Case 2, a half brother of the proposita, was short in stature, had cryptorchidism, and was trisomic for chromosome 28. Cytogenetic analysis of the dam, the sire of Case 1, and two other phenotypically normal half sibs revealed normal...
Hormonal changes associated with induced late abortions in the mare. Two mares received PGF-2 alpha twice daily until abortion and 2 mares received a combined treatment with oestradiol benzoate and oxytocin. The mares were about 150 days pregnant. The PG-treated animals aborted after 37 and 61 h, respectively, and the fetuses were expelled in intact fetal membranes. The other 2 mares aborted 13 and 27 h after the first oxytocin injection, respectively, and showed strong uterine contractions and expelled the fetuses in disrupted fetal membranes. Concentrations of 15-ketodihydro-PGF-2 alpha increased both after PG and oxytocin injections and in association with t...
Plasma prolactin concentrations in non-pregnant mares at different times of the year and in relation to events in the cycle. Plasma prolactin concentrations were measured in mares using an homologous radioimmunoassay. An annual rhythm in plasma prolactin was found, with concentrations higher during the summer than during the winter. In addition to this seasonal pattern, occasional high concentrations of prolactin were seen when concentrations were otherwise basal. Blood samples taken from mares during an oestrous cycle in October-November showed that prolactin values were basal for most of the cycle, with a marked rise in prolactin shortly before the onset of oestrus. This prolactin peak was associated with an incre...
Comparison of two reference preparations for horse chorionic gonadotrophin in four in-vivo and in-vitro assays. A number of horse chorionic gonadotrophin (CG) preparations of different purities and from diverse sources have been compared in radioimmuno-, radioreceptor, in-vitro cell culture, and in-vivo assays. The relative activities of the great majority of the preparations tested were consistent in the 4 assay systems. Moreover, their relative activities in the 4 assays were consistent with those found for unfractionated plasmas. These preparations were therefore considered to represent the native form of hormone. The second International Reference Preparation (IRP2) was among the few preparations ex...
Reproductive patterns in cyclic and pregnant thyroidectomized mares. Three Quarter-horse mares were thyroidectomized at about 1.5 years of age. Three similar intact mares served as controls. The study continued through two breeding seasons. The thyroidectomized mares were lethargic, rear limbs were oedematous and hair coats were coarse. They displayed a tranquil oestrous behaviour when exposed to a stallion and were only mildly antagonistic when not in oestrus. Length of oestrous cycles varied but most often they were 19-24 days long. Duration of oestrus (mean +/- s.e.m.) for the control and thyroidectomized mares was 12.9 +/- 2.9 and 11.7 +/- 2.2 days respecti...
Motility and ATP content of extended equine spermatozoa in different storage conditions. The role of various environmental conditions on sperm motility and ATP content was investigated by incubating raw and washed spermatozoa collected with an open-ended artificial vagina from 10 stallions in various biological and artificial media under different atmospheric conditions. Spermatozoa did not survive for more than 12 h when kept unextended in the original seminal fluid in any circumstances. The most favourable media tested for long-term sperm survival were Kenney's medium or Kenney's medium supplemented with 10 mM-theophylline and 10 mM-Hepes, pH 7.2. Centrifugation and slow cooling...
Use of different nonglycolysable sugars to maintain stallion sperm viability when frozen or stored at 37 degrees C and 5 degrees C in a bovine serum albumin medium. Bovine serum albumin (BSA) diluents containing lactose, raffinose or sucrose were not different (P greater than 0.05) in their ability to maintain stallion sperm viability, as determined by percentage motile spermatozoa (PMS) and their rate of forward movement (RFM), when stored at 37 or 5 degrees C for 24 h. These diluents did promote a higher (P greater than 0.05) PMS and RFM, when compared with BSA diluents containing arabinose or galactose. The BSA-arabinose and BSA-galactose diluents did not differ (P less than 0.05) in their ability to support sperm viability and were detrimental to sper...
Effects of inhibiting 3 beta-hydroxysteroid dehydrogenase on plasma progesterone and other steroids in the pregnant mare near term. Epostane, a competitive inhibitor of 3 beta-HSD was administered intravenously to a pregnant mare between 292 and 330 days of gestation at doses of 1-3 mg/kg/min. Plasma progesterone concentrations fell rapidly during epostane infusion in both the artery and uterine vein and remained significantly depressed for 4-5 h after the start of infusion. The venous arterial (V-A) plasma concentration difference in progesterone across the uterus also decreased significantly in response to epostane infusion. There were no significant changes in plasma progesterone or in the V-A concentration difference i...
Concentrations of uterine luminal prostaglandins in mares with acute and persistent endometritis. Intrauterine infusion of 1 per cent oyster glycogen solution was used to induce acute endometritis in four genitally normal mares. Numbers of viable neutrophils recovered in uterine washings had increased by 1 h after infusion and remained elevated for at least 72 h. There was a significant correlation between numbers of viable neutrophils and total protein concentrations and between prostaglandin (PG)F and PGE2 concentrations in washings. There was also a significant relationship between concentrations of 15-keto-13, 14-dihydro PGF2 alpha in plasma and PGF in washings. Intrauterine concentrat...
Steroid secretion by different cell types of the horse conceptus. Horse conceptuses were recovered non-surgically at Day 12-Day 15 and were dissociated with collagenase. Separation of the cells on a 31.8% Percoll gradient gave two bands of cells and indirect evidence suggests that the low density cells (LDC) are endoderm and the higher density cells (HDC) are trophectoderm. Each band was incubated for 24 h in Minimum Essential Medium and concentrations of oestradiol and progesterone in the medium were measured by radioimmunoassay (RIA). The LDC secreted predominately progesterone (log oestradiol/progesterone = -0.994 +/- 0.141; N = 15) whereas the HDC secret...
The pathogenesis of dystocia and fetal malformation in the horse. From a total of 601 severe dystocias in mares, 408 (68%) of the fetuses were in anterior, 95 (16%) in posterior and 98 (16%) in transverse presentation, compared with 99%, 1% and 0.1% respectively for spontaneous parturitions. From the cases with anterior presentation, 151 (37%) showed reflected heads and necks. From the cases with posterior presentation, 47 (50%) presented hip flexions, 25% had hock flexions, and 25% had stretched hind legs, 45 (47%) of the fetuses were in lateral or ventral position, and 28 (30%) of the fetuses were malformed (mainly torticollis and head scoliosis). All 98 c...
Evaluation of cellulose acetate/nitrate filters for the study of stallion sperm motility. Stallion semen was diluted in a Hepes-supplemented buffer (CM) (10(6) spermatozoa/ml) and placed in the upper well of a Sykes-Moore chemotaxis chamber. Chambers were incubated in a humidified atmosphere (5% CO2 in air) at 37 degrees C for 1 and 2 h and spermatozoa were allowed to swim through filters with a mean pore size of 3,5 or 8 micron. Spermatozoa entered filters of all three pore sizes. Distance travelled was greater for each increase in pore size (P less than 0.01) but did not differ (P greater than 0.05) between 1 and 2h of incubation. Extended semen from stallions of different fertil...
Reproductive characteristics of spontaneous single and double ovulating mares and superovulated mares. For embryos collected from mares 7 days after ovulation, embryo recovery for single-ovulating mares was 53% compared to 106% for double-ovulating mares. Pregnancy rates 50 days after surgical transfer were 68 and 129%, respectively. Concentrations of LH were similar during the periovulatory period for cycles which included single or double ovulations. Horse pituitary extract given for 5.5 days resulted in greater than or equal to 2 ovulations (mean 3.8) in 26 of 28 mares and 2.0 embryos were recovered per donor compared to 0.65 for controls. Non-surgical pregnancy rates for embryos collected f...
Cervico-endometrial cytology and physiological aspects of the post-partum mare. After parturition, Thoroughbred mares were mated at the first post-partum oestrus (N = 24) or at a subsequent oestrus (N = 12). All mares were examined daily for: oestrous detection, palpation per rectum of the genital tract, vaginoscopic examination and cervico-endometrial cytology. Pregnancy diagnosis was carried out at Days 18, 35 and 45 after mating. An identical first service conception rate of 50% was found in both groups. The number of neutrophils followed a descending profile to only scattered cells at the first post-partum oestrus and in Group II mares remained at this very low level ...
