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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.
Observations on the long term effects of Brucella abortus infection in the horse, including effects during pregnancy and lactation. Five mares and a stallion were studied from three to 30 months after experimental infection with Brucella abortus strain 544. The mares bred normally. No organisms were recovered from horses or from pregnant Friesian heifer contacts. Titres of serum antibody in the antiglobulin (Coombs) and complement fixation tests fell more slowly than those assessed by other tests. The serum of one foal yielded maternal antibody. An intradermal test was positive in infected adults only, and negative in all foals.
Development of a homologous equine relaxin radioimmunoassay. Equine relaxin (eRlx) immunoactivity has previously been measured in the mare during pregnancy using the porcine relaxin (pRlx) RIA (pRlx-RIA). This was not the optimal system for measurement of eRlx because the dose-response curve obtained with equine plasma was not parallel to the pRlx standard curve. A homologous eRlx-RIA has been developed and used to measure relaxin immunoactivity during pregnancy and parturition in the mare. Highly purified eRlx was used for the generation of antiserum in rabbits, preparation of tracer, and as assay standards. A double antibody eRlx RIA (eRlx-RIA) was de...
Concentrations of prolactin, luteinizing hormone and follicle stimulating hormone in pituitary and serum of horses: effect of sex, season and reproductive state. Pituitary and serum from 86 male or female horses of various reproductive states were collected in the normal breeding season (summer) and in the nonbreeding season (winter) at a commercial slaughterhouse. Concentrations of prolactin (PRL), luteinizing hormone (LH) and follicle stimulating hormone (FSH) were measured by radioimmunoassay. Concentrations of pregnant mare serum gonadotropin and reproductive steroids in serum and gross appearance of the reproductive tract and gonads were used to catagorize reproductive state. Concentrations of PRL were higher (P less than .01) in summer than in wi...
Active immunization of intact mares against gonadotropin-releasing hormone: differential effects on secretion of luteinizing hormone and follicle-stimulating hormone. Five lighthorse mares were actively immunized against gonadotropin releasing hormone (GnRH) to determine the relative importance of this hypothalamic hormone in the secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). Five mares immunized against the conjugation protein served as controls. Mares were initially immunized in November and received secondary immunizations 4 wk later, and then at 6-wk intervals until ovariectomy in June. All mares immunized against GnRH exhibited an increase (p less than 0.01) in the binding of tritiated GnRH by plasma, an indication that a...
Demonstration of the carrier state in naturally acquired equine arteritis virus infection in the stallion. The chronic carrier state was virologically confirmed in 15 thoroughbred stallions naturally infected with equine arteritis virus based on the results of test matings and, or, isolations of the virus from semen. Carrier stallions were shown to shed equine arteritis virus in the semen for at least one to two years. Existence of a short-term or convalescent carrier state was also demonstrated in five additional stallions. The frequency of the long-term carrier state in stallions naturally infected with equine arteritis virus was 35 per cent; it varied considerably between groups of stallions on ...
Purification and characterization of equine relaxin. It has been previously determined that the equine placenta is the sole significant source of relaxin during pregnancy and that relaxin immunoactivity is also present in term placentas. Therefore, placentas obtained at the time of foaling were selected for starting material for purification of equine relaxin. Frozen whole placentas were ground and then extracted with 0.5 N HCl-85% acetone. Relaxin was precipitated by raising the acetone concentration to 97%. Equine relaxin was further purified by stepwise elution ion exchange, gel filtration, and gradient elution ion exchange chromatographies a...
[Determination of progesterone levels in the milk of mares: a useful aid in the diagnosis of early pregnancy]. The concentration of progesterone in milk was determined in 327 mares to establish pregnancy in an early stage (sixteen days or more). The 5 ng/ml-level of progesterone as a threshold in the EIA-system used resulted in a very useful aid in the diagnosis of early pregnancy in mares. The results of testing were not in accordance with the confirmed reality in fourteen out of 327 mares (4.3 percent). The result of the test was false non-pregnant in five mares (1.5 percent) and false pregnant in nine mares (2.8 percent).
Evaluation of androgenized mares as an estrus detection aid. Ten pony mares that had developed stallion-like sexual behavior as the result of anabolic steroid treatment (boldenone undecylenate, 0.55 mg/kg intramuscularly (i.m.), once weekly for 12 injections) were evaluated for ability to aid in detecting estrus in cycling mares. In across-the-fence estrus detection trials, androgenized mares failed to elicit signs of estrus or diestrus. In 10-min pasture trials, in which each androgenized mare was placed in a group of 10 cycling mares (six of which were estrous), seven of the 10 androgenized mares elicited estrous behavior from one or two mares. Observ...
Behavior and viability of the premature neonatal foal after induced parturition. Parturition was induced in 2 groups of mares, less than 300 (n = 49) and 300 to 320 days gestation (n = 31), by the administration of prostaglandin F2 alpha or fluprostenol and oxytocin. Foals were categorized into 4 groups according to their ability to adapt in, and survive, the neonatal period. Group A had no demonstrable coordinating reflexes, were weak from birth, and all died within 90 minutes. Group B had some righting reflexes, but had poor coordination and a weak suck reflex. They showed some improvement for about 2 hours, but all died within 9 hours. Group C foals had a good suck refl...
A quantitative study of Sertoli cell and germ cell populations as related to sexual development and aging in the stallion. Testes from 47 stallions, 1-20 yr of age, were used to examine the influence of age on Sertoli and germ cell populations as well as on functional activity of Sertoli cells. For these stallions, the number of Sertoli cells per paired testes declined linearly with age, and was only 41.7% as great at age 20 as at age 2. However, development of reproductive organs proceeded until age 12-13, as evident from increases in paired testes weight and quantitative rates of spermatozoal production. Although the absolute number of Sertoli cells declined during this period of development, individual Sertoli ...
Plasma prolactin concentrations and cyclic activity in pony mares during parturition and early lactation. Five pony mares were blood sampled during late pregnancy, foaling and early lactation. An homologous assay for horse prolactin was used to measure plasma prolactin concentrations in these samples. Regular estimates of cyclic activity were also made. Plasma prolactin concentrations rose markedly in the last week of pregnancy and remained high although variable in early lactation, before declining to basal levels by 1-2 months post partum. All mares showed a post-partum oestrus 7.0 +/- 0.9 days after parturition. One mare whose foal died shortly after birth showed a rapid decline in plasma prola...
Daily rhythm of cortisol, and evidence for a photo-inducible phase for prolactin secretion in nonpregnant mares housed under non-interrupted and skeleton photoperiods. Studies were conducted in anestrous mares to characterize daily rhythms of cortisol in non-interrupted [ambient and 16 h light (L): 8 h dark (D)] and skeleton (10L:4D:2L:8D, 10L:6D:2L:6D and 10L:8D:2L:4D) photoperiods, and to determine if there exists a photosensitive phase for the secretion of prolactin. Neither peak or nadir concentrations of cortisol, nor the time of peak or nadir concentrations differed among photoperiod treatments. Highest concentrations (66 +/- 4.4 ng/ml, mean +/- SE) occurred between 0700 and 0900, whereas lowest concentrations (31 +/- 3.6 ng/ml) were found from 1900 to...
Relationships among serum immunoglobulin concentration in foals, colostral specific gravity, and colostral immunoglobulin concentration. Postpartum, presuckle, colostrum samples were collected from 100 mares. Colostral specific gravities significantly correlated (r = 0.9) with colostral immunoglobulin (Ig)G concentrations. Foal serum IgG concentrations highly correlated (r = 0.82) with specific gravities of the colostrum each foal ingested. Eight of 48 foals (17%) had serum IgG concentrations less than 400 mg/dl. The dams of these 8 foals had colostral sp gr less than 1.06 and colostral IgG concentrations less than 3,000 mg/dl. Foals had serum IgG concentrations greater than 520 mg/dl 24 hours after parturition, when the colost...
Effect of graded doses of gonadotrophin-releasing hormone on serum LH concentrations in mares in various reproductive states: comparison with endogenously generated LH pulses. Luteinizing hormone release induced by a range of small (3.3-33 micrograms) and large (300-500 micrograms) i.v. doses of gonadotrophin-releasing hormone (GnRH) was measured in acyclic (n = 4), luteal phase (n = 3) and follicular phase (n = 5) mares and compared with endogenously generated LH pulses in the same reproductive states. Extrapolation from log-linear dose-response curves showed that an LH pulse comparable to an endogenous one would be simulated by i.v. injection of 7.0 (n = 4) and 4.1 (n = 6) micrograms GnRH in luteal and follicular phase mares respectively; a much smaller dose than ...
Androgen and estradiol effects on gonadotropin secretion and response to GnRH in ovariectomized pony mares. In Exp. 1, 16 long-term ovariectomized pony mares were used to determine the effects of treatment with estradiol benzoate (EB) and dihydrotestosterone (DHT) benzoate alone, and in combination, on secretion of follicle stimulating hormone (FSH) and luteinizing hormone (LH) in daily blood samples and after three consecutive injections of gonadotropin releasing hormone (GnRH). Administration of EB alone, or in combination with DHT, every other day for 11 d reduced (P less than .05) concentrations of FSH and increased (P less than .05) concentrations of LH in daily blood samples, and increased (P ...
Two cases of abnormal equine pregnancy associated with excess foetal fluid. THE accumulation of a gross excess of fluid in the amniotic or
allantoic cavities is not uncommon in bovidae, although the
latter occurs most frequently. The resulting pathological
conditions are usually referred to as hydrops amnii and
hydroallantois, respectively. They are often associated with
abnormalities of the foetus in cattle (Vandeplassche el ul1965;
Roberts 1971) and hydro-allantois is quite common in twin
pregnancies (Roberts 1971).
This article describes two cases of excess foetal fluid in the
mare, both of which were associated with abnormal
pregnancies.
Comparison of the measurement of plasma testosterone and plasma oestrogens for the diagnosis of cryptorchidism in the horse. The results of performing 1720 blood tests for equine cryptorchidism are described. Using the paired sample human chorionic gonadotrophin (hCG) stimulation test and measuring testosterone, 6.7 per cent of tests did not give a clear result. If only the testosterone concentration in the pre-hCG blood sample was used, this percentage rose to 14 per cent. The paired sample hCG stimulation test was 94.6 per cent accurate. A comparison was made between the paired hCG stimulation test and the measurement of conjugated oestrogen in a single sample. The latter did not give as many doubtfuls but gave fa...
Induction of ovulation in anestrous mares with pulsatile administration of gonadotropin-releasing hormone. Four seasonally anestrous mares (Standardbred), housed under a nonstimulatory photoperiod of 8 hours light:16 hours dark, were administered gonadotropin-releasing hormone (GnRH) in a pulsatile pattern (50 or 250 micrograms of GnRH/hour) for 8 to 18 days during February and March 1985. Treatment with GnRH, irrespective of dose or month, induced an increase in serum luteinizing hormone from a mean pretreatment value typical of anestrus (0.58 +/- 0.02 ng/ml +/- SE) to 10.84 +/- 1.27 ng/ml on day 8 of GnRH treatment. Ovulation in the 4 mares occurred 8.8 +/- 0.7 days after the initiation of pulsat...
Effect of controlled exercise on libido in 2-yr-old stallions. Eight sexually inexperienced, 2-yr-old Morgan stallions were used in a consecutive two-phase design with two groups of four stallions each. Each phase lasted 16 wk, with semen collections every 14 d. Libido scores were assigned to stallions during each semen collection. Scores ranged from zero to four, with zero indicating minimum and four representing maximum libido. In Phase 1, four stallions received daily forced exercise for 16 wk, and the remaining four stallions were confined to box stalls. In Phase 2, the previously exercised stallions were confined to box stalls, and the non-exercised ...
Diagnostic ultrasound in equine reproduction. This article reviews the type of equipment available, the examination techniques, and the interpretation of information derived from ultrasound in broodmare practice. The application of diagnostic ultrasound has found immediate acceptability and clinical usefulness in the genital evaluations of the broodmare.
