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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.
Disappearance of spermatozoa from the ejaculates of geldings. Twenty-three geldings were used to determine changes in seminal characteristics following castration and the effect of frequency of ejaculation on these seminal characteristics. In Exp. 1, semen was collected from 8 geldings every other day after castration until the number of spermatozoa per ejaculate was below 1% of the precastration value. An average of 3 ejaculates was required to reduce the number of spermatozoa below this level. In Exp. 2, 15 stallions were castrated and each stallion was assigned to 1 of 3 groups for seminal collection at 7, 14 or 21 days post-castration. The ejaculates...
Isolation of Klebsiella pneumoniae from the urogenital tract of experimentally infected mares. K. pneumoniae capsule type 68 infused into the uterus of 4 mares was recovered up to 15 weeks after inoculation. The insertion of a tampon for 10 min was more effective than a swab technique in detecting the organism in the uterus. The clitoral fossa and the urethral orifice when sampled by the swab technique were also found to be infected for a comparable period. K. pneumoniae was isolated from the clitoral specimens more often and more consistently than from either urethral or uterine specimens.
Interaction of oestradiol and gonadotrophin-releasing hormone on LH release in the mare. Acyclic mare given oestradiol for 3 days to simulate the preovulatory plasma oestradiol surge showed a non-significant 37% decrease in plasma LH during treatment. When GnRH analogue injections were given with oestradiol on Days 1--3, oestradiol had no effect on each GnRH-induced LH increase, but LH increases were more prolonged following subsequent GnRH injections on Days 4--7 when oestradiol was no longer being given. A much greater prolongation of LH release occurred when the course of GnRH injections was commenced after oestradiol treatment ceased; the LH response was almost identical to th...
Specific PGF-2 alpha binding by the corpus luteum of the pregnant and non-pregnant mare. The binding of prostaglandin (PG) F-2 alpha to corpora lutea (CL) from pregnant and non-pregnant Pony mares was examined. Studies of the rates of association and dissociation indicated that [3H]PGF was bound specifically and reversibly to a luteal cell membrane preparation (MP) that was isolated by high speed (100,000 g) ultracentrifugation. Various PGs and PG metabolites displaced [3H]PGF from the receptors in the following decreasing order: PGF-2 alpha greater than 13, 14-dihydro-PGF-2 alpha = 13,14-dihydro-15-keto PGF-2 alpha greater than PGD-2 greater than PGF-1 alpha = PGE-2 greater than ...
Effect of ovariectomy on pregnancy in mares. Pony mares were bilaterally ovariectomized at different stages of pregnancy between Days 25 and 210. Abortion or fetal resorption occurred within 2 to 6 days after operations in all 14 mares ovariectomized between Days 25 and 45 and after an interval of 10 to 15 days in 9 of 20 other ovariectomized between 50 and 70 days. All 12 mares ovariectomized on either 140 or 210 days carried their foals to normal term. The termination of early pregnancy was preceded by a loss of uterine tone and of a palpable uterine bulge. The mean length of gestation in all mares in which pregnancy was not interrupte...
A precursor role for DHA in a feto-placental unit for oestrogen formation in the mare. Plasma levels of total oestrogens and dehydroepiandrosterone (DHA) were measured by radioimmunossay in samples taken from various blood vessels in both maternal and fetal compartments in 11 Pony mates. High concentrations of oestrogens (greater than 100 ng/ml of plasma), expressed as oestrone equivalents, were found in the fetal circulation. On both the fetal and maternal sides, oestrogen concentrations were lower in blood going to than from the placenta. DHA concentrations, on the other hand, were higher in blood flowing to the placenta from the fetus. The fetal gonads were seen as the source...
The correction of uterine torsion in a mare by caesarean section. A 9-year-old mare exhibiting signs of colic late in pregnancy was presented. Uterine torsion was diagnosed and corrected by caesarean section. A live foal was delivered and the mare survived the surgical interference.
Fertility of donor mares following nonsurgical collection of embryos. Embryos were collected nonsurgically on Day 7 or 8 after ovulation from 7 Quarter horse mares using a modified 30-ml Foley catheter to flush the uterine horn ipsilateral to the recent ovulation with 500 ml TCM-199 containing Hepes buffer. After collection, the uteri were infused with nitrofurazone to reduce the chances of infection due to the procedure. Eleven collections from 7 mares resulted in recovery of 9 embryos and nonsurgical transfer of 4 of these resulted in the birth of one foal. After collections, 8 oestrous cycles averages 22.75 days and 2 extended oestrous cycles were 43 and 59 d...
Contagious equine metritis–outbreak of the disease in Kentucky and laboratory methods for diagnosing the disease. Contagious Equine Metritis (CEM) was initially reported during the 1977 breeding season in England (Crowhurst, 1977) and Ireland (Timoney, Ward & Kelly, 1977. The disease has also been diagnosed in France and Australia (Huges, Bryden & MacDonald, 1978). The first occurrence of CEM in the United States followed the importation or 2 stallions from France late in 1977 which resulted in an outbreak early in the 1978 breeding season (Swerczek, 1978). Mares usually develop clinical signs of CEM 8--10 days after being covered by an infected stallion, when a copious, greyish discharge is seen. Other m...
Prolonged interovulatory interval after oestradiol treatment in mares. This study was designed to test if oestradiol treatment would prevent or delay luteolysis in mares. Mares (5/group) received 0, 0.1, 1.0 or 10.0 mg oestradiol-17 beta daily from the day of ovulation until the next ovulation or for a maximum of 32 days. This treatment did not prevent luteolysis which occurred 15.8, 16.8, 15.8 and 17.3 days after the previous ovulation for the mares treated with 0, 0.1, 1.0 and 10.0 mg oestradiol respectively. Although oestradiol treatment failed to alter oestrous behaviour after luteolysis, daily treatment with 10.0 mg oestradiol prevented follicular growth and...
Catecholamines and equine luteal progestagens. Corpora lutea (CL) from 7 mares were sliced and incubated for 2 h with ovine LH and various sympathomimetic agonists and blockers. None of these compounds was able to cause a significant increase in either progesterone or total progestagens by the luteal tissue. This is in contrast to earlier studies with bovine luteal tissue, and indicates that the equine CL is more refractory to exogenous stimulation than in the bovine CL.
Testicular measurements and reproductive characteristics in stallions. Factors affecting testicular measurements in situ and the relationships among the measurements and various reproductive characteristics were studied using data from 48 stallions. Mean values during the breeding season are provided for scrotal width, widths and lengths of individual testes, combined weight of testicular parenchyma, daily sperm production and daily sperm output. Testicular measurements were highly repeatable from day to day and for repeated measurements on a given day; technician provided the largest source of variation in the measurements of a given stallion. Age significantly ...
An investigation of seven enzymes as possible genetic markers in horse leucocytes. In this paper we describe seven enzymes, NP, GOTM, PGM2, alpha FUC, PEP A, ADA and MPI which are found in the white cells of horses, including 39 British crossbred ponies and 16 crossbred horses, 30 Mongolian ponies and 10 Icelandic ponies. Two of these enzymes--alpha FUC and MPI--were polymorphic in all the populations of horses studied and could prove useful as additional markers in the paternity testing of horses. PEP A and GOTM were also polymorphic in two of the populations studied and could be used as further markers in these populations.
Morphology of spermatozoa in semen from stallions of normal fertility. Semen samples were collected from 3 fertile stallions by means of an 'open' artificial vagina and examined under scanning and transmission electron microscopy. The stallion spermatozoon has many features in common with that of other mammals but differs specifically in that it has an asymmetric head, an abaxial position of the tail and an acrosome of small volume. The presence of microtubules in the neck is also a characteristic of stallion spermatozoa.
Changes in mammary development and composition of secretion during late pregnancy in the mare. Small samples of mammary secretion were taken for analysis from Thoroughbred mares during the last 3 weeks of pregnancy up to the time of foaling. The concentrations of sodium and chloride decreased while those of lactose, potassium, citrate, phosphate, calcium, magnesium and protein increased. The time-course of these changes showed marked variation between animals. The concentration of whey proteins began to increase about 10 days before parturition. The appearance of the secretion and the size of the mammary glands increased in the last few days of pregnancy. It is suggested that the concen...
Ovulation and the movement of the conceptus in the first 35 days of pregnancy in thoroughbred mares. Data from 937 Thoroughbred mares, when analysed as a single population, showed no significant difference between the activity of the right and left ovaries and the frequency of location of 35-day pregnancies in the right and left uterine horns. Nor were any differences shown when the data were analysed in years or sire groups. However, significantly more ovulations occurred in the right ovary in September and December and in the left ovary in October and November. Whereas the left and right ovulations were equal in lactating and dry mares, there was a highly significant increase in the number ...
Effect of successive ejaculation on stallion seminal characteristics. Five ejaculates were collected at hourly intervals from 32 sexually rested stallions. Gel volume, total seminal volume, sperm concentration and spermatozoa per ejaculate declined (P less than 0.01) from the first to the second or third ejaculate. Gel-free seminal volume or percentage of motile spermatozoa did not vary (P less than 0.05) among ejaculates. Ejaculates from 2- to 3-year-old stallions contained less volume and fewer spermatozoa than those from 9- to 16-year-old stallions. Regardless of the stallion's age the first, first 2, first 3 and first 4 ejaculates represented 50, 74, 86 and ...
Cytogenetic and clinical findings in mares with gonadal dysgenesis. Gonadal dysgenesis in the mare is associated with several different karyotypes, including sex chromosome aneuploidy (63,X; 63,X/64,XX; 63,X/64,XY or 65,XXX), the normal male complement (64,XY) and autosomal deletion (64,XX?del2q-). The 63,X is the most common karyotype found in gonadal dysgenesis. Aneuploid cases probably represent spontaneous chromosome non-disjunction during oogenesis, spermatogenesis or early embryonic development. Cases with XY or autosomal deletion may be inherited defects or of spontaneous origin.
The critical period for the maternal recognition of pregnancy in pony mares. Two experiments were performed to deterine the critical time at which the equine blastocyst must be present within the uterus of the mare to prevent regression of the corpus luteum, and thus establish the critical time for the maternal recognition of pregnancy. A non-surgical blastocyst collection technique was developed to study this relationship between the blastocyst and the maternal ovary. Results from these experiments demonstrated that the cyclic life-span of the corpus luteum is not affected by the presence of the blastocyst within the mare's uterus until after Day 14 after ovulation. L...
