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Topic:Equine Science
Equine Science encompasses the study of horses and their management, health, and performance. This field integrates various scientific disciplines such as biology, genetics, nutrition, physiology, and veterinary medicine to understand and improve the well-being and capabilities of horses. Areas of focus include equine anatomy, reproduction, behavior, and disease prevention. Research in equine science aims to enhance horse care, optimize training and performance, and address health challenges. This page compiles peer-reviewed research studies and scholarly articles that explore the diverse aspects of equine science, providing insights into the latest advancements and methodologies in the field.
Ovarian secretion of inhibin in mares. In mares, circulating immunoreactive inhibin concentrations increase during the follicular phase and decrease at the start of the LH surge. Thereafter, sharp increases in circulating immunoreactive inhibin concentrations, the 'ovulatory increase', are observed during ovulation. In the present study, the cellular sources and molecular form of ovarian inhibin were investigated to determine the mechanism responsible for this unique ovulatory increase. Three sizes of ovarian follicles (small, 30 mm in diameter) were selected. Inhibin alpha-subunit was localized by immunohistochemistry to the gran...
Intra- and inter-stallion variation in sperm morphology and their relationship with fertility. Dismount semen samples were collected from Thoroughbred stallions during the breeding season to determine the magnitude and significance of the variation in sperm morphology within (intra-) and among (inter-) stallions. The degree of intra-stallion variation in sperm morphology during the breeding season was substantial (coefficient of variation: 20%; range 8-56%), but did not affect the day-to-day fertility of sperm samples taken from the same stallion (intra-stallion). This variability did not affect the pregnancy rate of the mares with which each stallion was mated. The degree of interstall...
Influence of epidermal growth factor on in vitro maturation of equine oocytes. The effect of epidermal growth factor (EGF) on the in vitro maturation rate of equine oocytes was examined. Oocytes were collected from an abattoir (Expt 1) or using ultrasound-guided follicular puncture in vivo (Expt 2). All oocytes with a compact or expanded cumulus at recovery were cultured for 30 h in: medium 1 (TCM199 + fetal calf serum (FCS) + crude equine gonadotrophin (CEG) + oestradiol + antibiotics); medium 2 (TCM199 + EGF); medium 3 (medium 1 without FCS + EGF); or medium 4 (medium 1 without CEG + EGF). In Expt 1, 84% (37/44) and 87% (40/46) cumulus expansion (P > 0.05), and 39% (22...
Oviductal insemination of mares. A technique was developed for oviductal insemination of mares, in which a small number of motile spermatozoa are deposited directly into the oviduct. Pregnancy rates in mares inseminated by traditional intrauterine artificial insemination were compared with rates in mares inseminated by oviductal insemination. Fifteen mares were inseminated with 5 x 10(8) progressively motile spermatozoa by intrauterine artificial insemination, and 14 mares were inseminated with 5 x 10(4) progressively motile spermatozoa by oviductal insemination. Pregnancy rates in mares inseminated by intrauterine artificial...
Oxytocin administration prolongs luteal function in cyclic mares. Recent evidence indicates that, in mares, as in the domestic ruminants, oxytocin and its endometrial receptor play important roles in stimulating the pulsatile releases of prostaglandin F2 alpha from the endometrium that effect luteolysis. In the present experiment, continuous administration of oxytocin by subcutaneous minipump to five mares during days 8-20 after ovulation abolished luteolysis in four of them, while all four of the control mares infused similarly with saline underwent luteolysis at the expected time. When oxytocin administration began on day 10, instead of on day 8, after ovu...
Quantitative histological analysis of equine embryos at exactly 156 and 168 h after ovulation. Equine embryos were collected at exactly 156 +/- 0.5 (n=8) and 168 +/- 0.5 h (n=11) after ovulation. The embryos were fixed in glutaraldehyde, sectioned serially and observed using light microscopy. In the 156 h group, all embryos were early blastocysts except for one, which was a morula. The morula and one early blastocyst had no capsule. The capsules of the other embryos were thin. The mean +/- SD total number of cells was 275 +/- 105 (range 117-417). The mean +/- SD proportions of mitotic and pycnotic cells were 2.5 +/- 1.2 and 1.1 +/- 1.8%, respectively, and there were no differences betwe...
Determination of minimum light treatment required for photostimulation of winter anoestrous mares. Classical photostimulation of winter anoestrous mares consists of a light treatment with 14.5-16.0 h white light (100 lux), starting near the time of the winter solstice and ending around the time of the summer solstice. Cyclicity is obtained typically after about 70 days of treatment. The aim of the present study was to establish the minimum number of days of treatment, the lowest light intensity and the duration of light required per day to advance the onset of ovarian activity in winter anoestrous mares. In Expt 1 it was demonstrated that a 35 day exposure to a photoperiod (14.5 h light: 9....
Transport of spermatozoa in the reproductive tracts of mares. A scintigraphic method was developed to study sperm migration in the reproductive tracts of mares. Mares (n=5) and stallions (n=2) were used to test various steps of the procedure and three other mares and a stallion were used to study sperm transportation. A radiolabelling solution was prepared from 99mTc (Technetium-99m) and hexamethyl propylene amine oxime. The highest labelling of spermatozoa (57-72%) was obtained by incubation of the spermatozoa with the radiolabelling solution for 20 min at 20 degrees C. Radioactivity outside the spermatozoa was removed by centrifugation and by two subse...
Effect of cryopreservation and oviductal cell conditioned media on Ca2+ flux of equine spermatozoa. Movement of Ca2+ into spermatozoa is a critically important event for capacitation and the acrosome reaction. In the present study, the nature of Ca2+ movement in fresh equine spermatozoa was established and the effects of oviductal cell conditioned medium (OCM) and cryopreservation on Ca2+ flux were investigated. The ability of fresh and cryopreserved stallion spermatozoa to regulate Ca2+ concentration over time was evaluated in Ca2+ -free PBS. Intracellular Ca2+ concentrations were higher in cryopreserved spermatozoa than in fresh spermatozoa. However, extracellular Ca2+ concentrations were ...
Effect of cholesterol on the motility and plasma membrane integrity of frozen equine spermatozoa after thawing. The aim of the present study was to investigate the cryoprotectant properties of cholesterol after incorporation into the plasma membranes of equine spermatozoa. A cholesterol-methyl-beta-cyclodextrin complex was used to alter sperm plasma membrane cholesterol content. Ejaculates from six stallions were centrifuged in a non-fat skimmed milk glucose-sucrose extender (MK) or a modified Tyrode's medium (TALP). The sperm pellets were resuspended in the appropriate extender with or without added cholesterol (0.125 mmol cholesterol-methyl-beta-cyclodextrin complex l(-1)) and incubated at 24 degrees ...
Zona pellucida-sperm binding assay for equine oocytes. The binding of a spermatozoon to the zona pellucida is the first step in fertilization. The number of spermatozoa bound to a zona pellucida may reflect the functional status of both the oocyte and spermatozoa. The aim of the present study was to determine whether the stage of maturation of the equine oocyte affects the capacity of the zona pellucida to bind with spermatozoa. Cumulus-oocyte complexes (COCs) were collected from the ovaries of mares from abattoirs or were obtained in vivo by ultrasound-guided follicular aspiration. Oocytes were inseminated directly after collection or after 30 h ...
Freezing of stallion semen: interactions among cooling treatments, semen extenders and stallions. In the present study, the interactions among stallions, semen extenders and cooling treatments before stallion semen samples were frozen were studied. In Expt 1, the effects of four cooling treatments and three semen extenders were investigated (11 stallions x four split ejaculates), whereas in Expt 2, the effects of two semen extenders, two egg yolk concentrations and two glycerol concentrations were investigated (six stallions x five split ejaculates). Sperm motility after thawing was evaluated. In Expt 1, the extender x cooling treatment interaction was significant. Centrifugation and addit...
Ultrastructure, protein phosphorylation and mRNA status of equine oocytes matured in vivo and in vitro. Equine oocytes were collected by follicle aspiration in vivo or by dissection of material obtained from an abattoir, and the ultrastructure, protein phosphorylation and mRNA status of the oocytes were evaluated. Electron microscopy studies indicated that the nucleus had a smooth membrane in oocytes with a compact cumulus, whereas the nuclear membrane was undulated in all other groups. Oocytes with compact cumuli had only a few microvilli, whereas those with expanded cumuli had more microvilli. There were only small numbers of cortical granules close to the oolemma in oocytes with compact cumul...
Dopamine antagonist-induced reproductive function in anoestrous mares: gonadotrophin secretion and the effects of environmental cues. The effect of the dopamine antagonist sulpiride on FSH secretion and onset of reproductive activity in anoestrous mares under different environmental conditions was investigated. In Expt 1, sulpiride (0.5 mg (-)-sulpiride kg(-1) twice a day) had no affect on FSH pulse frequency, mean FSH concentration, basal FSH concentration or FSH pulse amplitude in anoestrous mares. These data do not support the hypothesis that dopamine inhibits reproductive activity by suppressing GnRH secretion, as it does in other species. In Expt 2, the interval to first ovulation (14.8 +/- 1.9 days; range 12-22 days) i...
Testicular secretion of inhibin in stallions. In this study, clear seasonal changes in the circulating concentrations of immunoreactive inhibin were observed in stallions throughout the year. The highest plasma concentrations of immunoreactive inhibin were observed during the breeding season and the lowest concentrations were observed during the nonbreeding season. There was positive correlation between the circulating concentrations of immunoreactive inhibin, steroid hormones and gonadotrophins. Inhibin alpha subunit positive staining was observed in Sertoli cells and more clearly in Leydig cells. Both cell types also stained positively ...
Effect of L-glutamine for freezing equine embryos: evaluation by DAPI staining and transfer of multiple embryos to recipient mares. Day 6.5 equine embryos (n=30) were frozen in a medium containing glycerol (2.5-10.0%) supplemented with 0, 20 or 100 mmol L-glutamine 1(-1). After thawing, the embryos were tested individually, using 4',6'-diamidino-2-phenylindole (DAPI) staining to evaluate cell death. Three embryos (one frozen at each L-glutamine concentration) were transferred together into individual recipient mares. Pregnancy diagnosis was performed at day 12 (age of embryo). Embryos were collected at day 14 (age of embryo) and were identified by PCR amplified microsatellite analysis. Nine of ten recipient mares that rece...
Evaluation of equine fetal growth from day 100 of gestation to parturition by ultrasonography. Transrectal and transabdominal ultrasonography were performed on normal pregnant mares (n=10) at 2 week intervals from day 100 of gestation to parturition to evaluate fetal growth. Several fetal anatomical regions (head, eye, aorta, abdomen, rib, gonad, kidney and femur) were imaged and measured using standardized scan plans. The results of these analyses indicate that all of the biometric parameters correlate strongly with the day of gestation. Growth charts were developed, which demonstrate that the following variables have linear relationships with the day of gestation on which they were me...
Motility, morphology and triple stain analysis of fresh, cooled and frozen-thawed stallion spermatozoa. The aim of the present study was to determine whether there are characteristics of fresh, cooled and frozen-thawed semen samples that can be used to predict the suitability of stallion semen for preservation by cooling or freezing. Each of three ejaculates obtained from 12 stallions was divided into aliquots to be analysed for sperm motility, morphology and membrane integrity as fresh, cooled and frozen-thawed samples. The percentage of morphologically normal spermatozoa was similar in fresh and cooled samples and both were greater than in the frozen samples. There were no strong linear relati...
Maternal influence on pre- and postnatal growth of foals born after embryo transfer. In the present study the growth and development of three pairs of matching gender foals from birth to maturity were compared. One Polish Pony embryo of each pair was transferred from a donor mare (mass 387-400 kg) to a much larger heavy type recipient mare (mass 561-780 kg). The other embryo of each pair underwent normal gestation (control). The transferred and control horses were examined at 9 and 13 years of age, and X-ray pictures were taken of their front legs to measure the length of the bones. On the basis of the results of this study, it is concluded that the processes of growth and dev...
Partial characterization of an equine conceptus prostaglandin inhibitory factor. Equine conceptuses are thought to produce antiluteolytic factors that inhibit endometrial PGF2alpha and, thus, prevent luteolysis in pregnant mares. The aim of the present study was to characterize partially the chemical nature of the prostaglandin inhibitory factor (PIF) produced by equine conceptuses in vitro. Embryos were collected from pregnant mares 13 +/- 0.5 days after ovulation and were cultured for 24 h. Harvested equine conceptus conditioned media (CCM) were assayed for antiluteolytic activity by determining the inhibition of endometrial PGF2alpha synthesis in vitro. Significant anti...
Apoptosis in equine granulosa cells and its relationship to cumulus expansion and oocyte chromatin configuration in ovarian follicles. During the oestrous cycle follicles grow and either ovulate or regress. Regressing follicles undergo atresia and in many species apoptosis has been identified as the underlying mechanism in this process. The aims of this study were to establish whether equine granulosa cells degenerate via an apoptotic mechanism and whether the presence of apoptotic cell death in granulosa cells is correlated with oocyte quality. Ovaries from mares at unknown stages of the oestrous cycle were obtained from an abattoir. In Expt 1, follicles (n=352) from 37 mares were processed. DNA was extracted from granulosa ...
Indirect determination of stallion sperm capacitation based on esterase release from spermatozoa challenged with lysophosphatidylcholine. A spectrophotometric assay was developed to measure the amount of esterase released from stallion spermatozoa. This assay was used to determine the percentages of capacitated stallion spermatozoa, determined by the ability of spermatozoa to undergo an acrosome reaction and release esterase in response to a lysophosphatidylcholine challenge, for spermatozoa incubated under conditions to increase intracellular calcium and cAMP. Incubation with 100 nmol calcium ionophore A23187 l(-1) induced 66% of stallion spermatozoa to capacitate after 60 min of incubation at 37 degrees C. Subsequent experimen...
Estimation of sodium and potassium concentrations in the uterine fluid of mares by microdialysis and ion chromatography. Equine blastocyst fluid has a lower [Na+], a higher [K+] and a lower osmolality than does normal blood serum. Based on the assumptions that the sodium pump is primarily responsible for fluid accumulation and that ions transported actively into the blastocyst increase blastocyst osmolality above that of the external medium, we hypothesized that the [Na+] and the osmolality of mare uterine fluid are lower than those of blastocyst fluid. Microdialysis and ion chromatography were used to estimate [Na+] and [K+] of uterine fluid. Mares (n=10) were used for in vivo measurements at different stages o...
The uterus as a source of oxytocin in cyclic mares. In a recent study, continuous administration of oxytocin by subcutaneous minipump to mares from day 8 to 20 after ovulation prevented luteolysis in most of the treated but none of the control mares, indicating a role for oxytocin in cyclical luteolysis in mares. In the present study, measurement of oxytocin concentrations in uterine flushings recovered from nine mares during days 14-18 after ovulation gave values that were many times higher than those measured concurrently in peripheral plasma. Furthermore, intrauterine administration of oxytocin to four mares on day 14 after ovulation stimula...
The structural morphology and epithelial association of spermatozoa at the uterotubal junction: a descriptive study of equine spermatozoa in situ using scanning electron microscopy. Uterotubal junction tissues (n=12) recovered from young nulliparous mares 4 h after insemination were examined for spermatozoa in situ using scanning electron microscopy. Mares were inseminated before ovulation with semen containing 66-85% morphologically abnormal spermatozoa and approximately 1 x 10(9) progressively motile spermatozoa. Spermatozoa were found in all the tissues and displayed a variety of relationships to the epithelium, depending on regional location, spatial constraints and epithelial surface characteristics. Spermatozoa were most abundant in the epithelial folds on the uteri...
Simultaneous recording of pituitary oxytocin secretion and myometrial activity in oestrous mares exposed to various breeding stimuli. The aim of this study was to investigate the effect of different breeding stimuli on uterine contractility and pituitary oxytocin release in five oestrous mares, in order to design better treatments for mares with defective physical uterine clearance mechanisms. Electrodes and strain gauges were implanted surgically on the uterine myometrium and myometrial activity was monitored with a Grass polygraph. A catheter was placed non-surgically in the intercavernous sinus of each oestrous mare to sample pituitary venous blood and a second catheter was placed in the jugular vein. Continuous sampling ...
Preservation of stallion sperm quality by native phosphocaseinate: a direct or indirect effect? Milk-based diluents are generally considered efficient for survival of stallion spermatozoa in vitro. However, milk is a complex and variable medium and native phosphocaseinate is a milk component that is more efficient for preservation of sperm motility and fertility, although the mechanisms involved in this protection have not yet been elucidated. The aim of the present study was to characterize the interactions between native phosphocaseinate and equine spermatozoa. No binding between sperm membranes and native phosphocaseinate was observed using indirect immunofluorescent staining or elect...
Effect of increased daylight during late pregnancy on the reproductive performance of mares after parturition. The aim of the present study was to determine the effect of prolonged photoperiod during late pregnancy on subsequent ovarian activity and fertility in mares. Pregnant mares (n=13) due to give birth in January and February were stimulated by a fixed photoperiod (16 h light: 8 h dark) from 15 November (during the last 2-3 months of gestation) until up to 1 month after parturition. A control group of mares (n=9) due to give birth at the same time were kept in the same stable and management regimen, but under natural light conditions. Light-treated mares ovulated during foal oestrus approximately...
Production of live foals from sperm-injected oocytes harvested from pregnant mares. In vitro fertilization in horses has been less successful than anticipated owing to: (i) the inability to collect large numbers of good quality oocytes; (ii) alterations in the zona pellucida that occur during in vitro maturation of equine oocytes; and (iii) inadequate preparation of equine sperm cells. In addition, studies in humans, mice and cattle have indicated that high concentrations of glucose in culture media may inhibit embryonic development in vitro and this may also be a problem for development of equine embryos in vitro. The aims of the present study were: (i) to achieve fertilizat...
Relationship between the degree of endometrial periglandular fibrosis and the presence of angiotensin-converting enzyme in the equine endometrium. Endometrial periglandular fibrosis (EPF) has been proposed as a possible aetiology for equine embryonic and fetal loss. However, the pathophysiology of EPF is not well understood. Angiotensin-converting enzyme (ACE) is found in macrophages, endothelium (during angiogenesis) and myofibroblasts at sites of fibrosis in the heart, kidneys, liver and skin in several species. An increase in local tissue ACE-binding activity appears to be a critical event in the initiation and progression of fibrosis in these tissues. The aim of this study was to investigate the correlation between ACE activity in th...
