Omneity® Pellets
All-In-One Vitamin & Mineral Pellet
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.
The site of ovulation in the mare. Serial photography of the ovary of a mare by periodic surgical exteriorization of the ovary and peritonescopy in situ revealed that the ovulatory fossa is the site of ovulation in this species.
Infection of the horse fetus. Many infections of the equine placenta and fetus result from ascending spread along the cervical canal. Most abortions due to infection occur during the later stages of pregnancy and the possible effects of intrauterine infection on the developing fetus and young foal are discussed.
The contribution of the mule to scientific thought. The infertility of the mule has proved a continuing challenge to scientific thought. Since the chromosomal differences between the two parental species are so great as to render normal meiosis impossible, it is postulated that all mules and hinnies are sterile. The problem now is to explain how mules and hinnies can occasionally produce spermatozoa or ova. The appearance of the mule was sufficient to persuade the ancients that both parents, not just the male, must contribute to the make-up of the offspring. The mule has also taught us that, when the number of oocytes in the ovary is reduced, t...
Oestrogen excretion in mares in relation to various reproductive states. The rate of urinary oestrogen excretion was studied in four ovariectomized mares. In two animals ovariectomized when urinary oestrogen concentration was high, levels fell to a minimun within 48 hr. Intramuscular injection of oestradiol-17beta produced maximum urinary oestrogen levels within 3 to 6 hr and a return to minimum detectable levels within 24 hr. The major urinary oestrogen in mares was oestrone. In nine maiden mares studied between September and June, the cycle, the durations of dioestrus and oestrus, and the time of ovulation were similar in autumn (September to December) and spring...
Follicular and luteal development in pregnant mares. Examination of the ovaries of mares at various stages of pregnancy and after hysterectomy, together with measurement of progesterone concentrations in the peripheral plasma of pregnant and hysterectomized mares and in uterine and ovarian venous plasma of pregnant mares, demonstrated that the primary CL of pregnancy remains functional until at least Day 160 of gestation. The results showed that primary and secondary CL, and the placenta or uterus, all contribute to the total progesterone pool in mares during pregnancy. Similarities and differences in ovarian function observed between pregnant a...
Oestrone and equilin in the plasma of the pregnant mare. A method for the extraction of oestrone and equilin from the plasma of the pregnant mare is described, and the levels obtained for eighty-two samples from fourteen Welsh Mountain Ponies at different stages of pregnancy are recorded. Oestrone (fifteen samples) and equilin (three samples) were not found before Day 120. From Day 120 to 240, oestrone levels exceeded 100 ng/ml and then declined to parturition. The high concentrations of oestrone in mid-pregnancy were associated with gradually increasing concentrations of equilin which tended to plateau after Day 180 at just under 100 ng/ml and decl...
Early pregnancy testing and its relationship to abortion. A total of 487 Standardbred and Thoroughbred mares at two studs were manually tested for pregnancy at 20 to 24, 30 to 34, and greater than 42 days after service and the abortion rate compared to that obtained in previous years when only the greater than 42-day test was performed. The results indicated that early manual pregnancy testing does not increase the abortion rate if undertaken carefully and enables non-pregnant mares to be re-mated earlier in the same season.
A review of cytogenetics in equine reproduction. The karyotype of the horse consists of 64 chromosomes; 18 pairs have a terminal centromere and 13 pairs a non-terminal centromere. Identification of individual chromosomes is enhanced by the use of band-staining techniques which allow recognition of minor structural rearrangements of chromatin material. Seven previously reported cases of male pseudohermaphroditism with chromosome studies are reviewed. Three were genetic females, one was basically an XX/XY chimaera, one was an XX/XXY chimaera, and one was an XXXY. Also reviewed is an infertile mare with 63 chromosomes and no distinguishable sex...
Sperm transport and distribution in the mare. Fifty mares were inseminated on Days 2, 4, 7, 11 or 17 of the oestrous cycle with spermatozoa from one of three stallions to observe the distribution of the spermatozoa in various parts of the reproductive tract 12 hr later (Days 3, 5, 8, 12 and 18). Only 0-06 to 2-21% of inseminated spermatozoa were recovered from the tract. More (P less than 0-05) spermatozoa were recovered from the cervix and uterus on Day 12 than on Days 3, 5, 8 and 18. The mean number of spermatozoa recovered from either or both oviducts was significantly greater (P less than 0-10) on Days 5 and 8 than on Days 3, 12 and 1...
Duration of oestrus and time of ovulation in mares treated with synthetic Gn-RH (AY-24,031). Synthetic Gn-RH, administered during oestrus, stimulates the release of pituitary LH in the cyclic mare. Duration of oestrus was significantly reduced by 1 mg Gn-RH given on Day 2 of oestrus; the time of ovulation, measured in days from the onset of oestrus, also tended to be reduced. An injection of 2 mg Gn-RH had nor further effect, but daily injections from Day 2 until ovulation significantly shortened the duration of oestrus and the time to ovulation. The profiles of LH were found to be variable from mare to mare, but in all mares, treated and control, elevation of LH was detected close to...
Effect of exogenous progesterone on its endogenous levels: biological half-life of progesterone and lack of progesterone binding in mares. The disappearance rate of progesterone from blood plasma of an ovariectomized mare was rapid and occurred in three phases. The half-life of the first component was 2-5 min and that of the second was 20 min; the half-life of the much slower third component was not measured. Progesterone, administered to ovariectomized and deeply anoestrous mares at the rate of 150 or 300 mg/day, maintained maximal peripheral levels of 6 to 8 ng/ml. Physiological levels were reached in 21 days using a dose of 150 mg and in 11 days with 300 mg daily. After withdrawal, circulating levels dropped rapidly. Blood pla...
Origin and histogenesis of equine endometrial cups. Biochemical and morphological studies were carried out to determine the origin and histogenesis of endometrial cups in mares. A wide range of fetal and maternal tissues were cultured in vitro and their ability to secrete gonadotrophin (PMSG) was monitored. High levels of PMSG were produced in culture only by cells from the restricted area of the equine trophoblast known as the chorionic girdle which is an annular band of highly specialized cells at the junction of the allantois and the regressing yolk sac. The morphological appearance of girdle cells after cultivation in vitro and after alloge...
Effects of artificial light on the oestrous cycle of the mare. Two groups, each of seven pony mares, were maintained from 17 October to 15 February (120 days) in the University Biotron where temperature and daily photoperiod were regulated to simulate normal conditions for that period (control group) or those normally applicable from 1 March to 1 July (treated group). Follicular growth, ovulation rate and oestrous behaviour were determined daily by rectal palpation, and by teasing with a stallion. By Day 69 of treatment, all ovarian end-points (number of follicles greater than 10 mm, number of follicles greater than 20 mm, average follicle diameter and di...
The frequency of infertility in thoroughbred mares. In a group of 852 Thoroughbred mares, 69-7% had foals which survived beyond 6 weeks, 7-1% had dead, premature or full-term foals and 1-1% had foals which died within 6 weeks after birth. Possible factors which may have influenced these data are mentioned.
Results of insemination of mares with fresh and frozen stallion semen. Artificial insemination using deep-frozen semen was performed on 116 mares in 1973 using twelve ejaculates from eight stallions of the Hanoverian breed. Despite the fact that the quality of the semen used was poor, the majority of the mares inseminated were subfertile and some mares were inseminated during one oestrus only, 44% nevertheless conceived and gave birth to live foals. Of a small group of ten mares inseminated in the same year with fresh semen, seven conceived.
Influence of intrauterine saline infusion upon the oestrous cycle of the mare. The effect of intrauterine saline on reproductive function was studied by infusion of mares in anoestrus, dioestrus, oestrus and prolonged dioestrus. Anoestrous mares were unaffected except near the beginning and end of the breeding season when anovulatory heats were induced. Dioestrous mares infused between Days 5 and 9 returned to heat an average of 3-8 days earlier than expected, and infusions during dioestrus were followed by ovulatory heats of normal fertility. Three mares in prolonged dioestrus showed ovulatory heats within 3 to 9 days of infusion. Infusions during oestrus had no appreci...
A review of the influence of nutrition upon the oestrous cycle and early pregnancy in the mare. Attention is drawn to the beneficial effect of improved nutrition during winter and early spring on the ovarian activity of mares. Furthermore, the necessity of an adequate plane of nutrition during early pregnancy to prevent embryonic resorption is stressed.
Plasma progestagens in pregnant mares. Peripheral plasma progestagens were quantified by a competitive protein-binding assay throughout pregnancy. The level of progesterone increased significantly between Days 0 and 8 (P less than 0-05) and again between Days 28 and 44 and reached a maximum on Day 64. Subsequently, it fell slowly until about Day 300 and then rose again during the last 30 days before reaching a minimum on the day after foaling. Very low concentrations of 17alpha-hydroxyprogesterone were found except between Days 40 and 120 and during the last 30 days before birth. Two unidentified compounds, one eluting slightly bef...
Ovarian changes during early pregnancy in pony mares in relation to PMSG production. The ovaries of twenty pregnant mares were examined daily, per rectum, for the first 4 months of gestation and note was made of their estimated size and follicular content. Serial blood samples from sixteen of the mares were assayed for PMSG. A marked seasonal effect was noted on ovarian size, follicular content and ovulation rate during pregnancy but there was no such effect on PMSG production. It is concluded that PMSG is synergistic with gonadotrophins of pituitary origin and that the latter hormone are the primary stimulus on the ovary of the pregnant horse.
The evaluation of stallion semen in aspects of fertility control and its use for artificial insemination. Choice of the best methods for semen examination is dictated by the purpose of the examination, whether it be to assess the fertility of an individual stallion or to evaluate individual semen samples for routine purposes. In the author's experience of examining stallion semen, emphasis should be placed upon morphological examination, sperm cinematography and survival tests in vitro. Special problems concerning examination of frozen semen are discussed and the ultrastructure of spermatozoa frozen in the presence and absence of glycerol is described.
The influence of fetal genotype upon endometrial cup development and PMSG and progestagen production in equids. The influence of fetal genotype upon gonadotrophin (PMSG) and progestagen production in mares and donkeys during the first half of pregnancy was examined. The production of PMSG was greatly reduced in mares carrying mule conceptuses and greatly increased in donkeys carrying hinny conceptuses. Fetal genotype had no obvious influence upon progestagen production in mares, but donkeys carrying hinny conceptuses showed extremely high peripheral plasma progestagen concentrations when serum PMSG levels were elevated. Fetal genotype profoundly influences the intensity and rate of success of the matern...
Effect of timing of insemination, numbers of spermatozoa and extender components on the pregnancy rate in mares inseminated with frozen stallion semen. Fertilization rate was highest in mares inseminated with frozen semen within 12 hr of ovulation. Foaling rate was improved (P less than 0-05) by increasing the number of motile spermatozoa inseminated from 40 X 10(6) to 80 X 10(6) but was not further improved by increasing the number to 160 X 10(6) or by increasing the frequency of insemination from once to twice daily. The fertilizing capacity of spermatozoa frozen in one of the hydrogen ion extenders studied was dependent upon relative osmotic pressure and method of freezing (ampoules or pellets). Adjusting glycerol concentration from 7% to ...
Effects of prostaglandin F2alpha on the oestrous cycle and pregnancy in mares. Several experiments indicated that prostaglandin F2alpha (PGF2alpha) has luteolytic and abortifacient properties in mares. A single subcutaneous injection of 1-25 mg PGF2alpha on Day 6 of dioestrus was as effective as 10 mg PGF2alpha in inducing luteolysis. Oestrus and ovulation appeared to be synchronized when a single injection of 1-25 mg PGF2alpha was given on Days 7, 10 or 13 after ovulation but not on Days 1 or 4 after ovulation or on Day 2 of oestrus. Intramuscular administration was as effective as subcutaneous administration and 1-25 mg PGF2alpha was the minimal effective systemic dose...
Synchronization of oestrus in mares with a prostaglandin analogue and HCG. Following an initial observation period of 13 days when plasma progesterone levels were determined, synchronization of oestrus and ovulation was investigated in thirty-three mares treated with a prostaglandin analogue ('Equimate') and HCG. Two courses of treatment were given 8 days apart and each consisted of a single intramuscular injection of Equimate (250 mug) followed 6 days later by an intramuscular injection of HCG (2500 i.u.). The first course was designed to remove all luteal tissue and to induce ovulation of any follicles that developed in response to the withdrawal of progesterone. T...
Results of artificial insemination of horses in Poland in the post-war period. Artificial insemination (A.I.) of mares in Poland has not yet been widely applied. Initial attempts were made by research groups between 1945 and 1955 but A.I. of mares was only introduced into the normal practice of A.I. Centres during 1964-67. Intensive research into methods for preserving stallion semen in liquid nitrogen has been undertaken since 1968. Of the total of 3734 mares artificially inseminated in Poland since 1945, 350 were inseminated with frozen semen. The slow progress of A.I. in horses is imputed to the small numbers of people involved in the work, to the conservation of the ...
Serum concentrations of FSH, LH and progesterone during the oestrous cycle and early pregnancy in the mare. Heterologous radioimmunoassays were developed for equine FSH and LH. Serum concentrations were measured in twenty-three mares throughout the oestrous cycle and early pregnancy. FSH concentrations were raised fivefold by 'surges' rather than 'spiked', occurring at 10- to 11-day intervals during the oestrous cycle and early pregnancy. The late oestrous/early dioestrous surge of FSH appeared to initiate development of up to twenty follicles. The mid-dioestrous surge may be important for the further development of follicles destined to ovulate 10 to 13 days later. Levels of LH were increasing by t...
The oestrous cycle of the mare. In eleven non-pregnant mares examined for 2 years, oestrous cycle length was 20-6 days (range 13 to 34) excluding any anoestrous periods. The duration of oestrus was 5-7 days (range 1 to 24); from February to May it was 7-6 days (range 2 to 24) and from May to November 4-8 days (range 1 to 10). The majority of ovulations occurred between 16.00 and 08.00 hours and 78% of the mares ovulated within 48 hr of the end of oestrus. Mean follicular diameter was 45 mm on the day of ovulation and there was a 25-5% incidence of multiple ovulations. It was uncommon for oestrus to occur without ovulation, w...
Plasma progestagens and oestrogens in fetus and mother in late pregnancy. Normal Thoroughbred and catheterized Pony mares and their fetuses were used. Fetal oestrogen and progestagen concentrations in late gestation were much higher than maternal values. A major feature of the umbilical steroid concentrations was a large venous-arterial difference in progestagens and total oestrogens throughout late gestation which may indicate a metabolic cycle in the fetus between progesterone and other steroid metabolites. Metabolites of 20alpha-dihydroprogesterone were present in high concentrations in maternal and fetal plasma. In Thoroughbreds, and to a lesser extent in Pony m...
Ejaculatory disorders of the stallion. Ejaculatory disorders of the stallion seem to occur more frequently than hitherto accepted. The condition is manifested differently in individual stallions from normal copulation without ejaculation to an abnormal pattern of copulation without or with occasional ejaculation. The condition is probably caused by a functional disturbance of the nervous mechanism which controls the ejaculatory process, and may be caused by environmental or other factors. Eleven cases of ejaculatory disorders in normal healthy stallions were investigated and three of these animals recovered after simple correction ...
The use of Gn-RH for controlling the oestrous cycle of the mare (preliminary report). Clinical tests with synthetic gonadotrophin-releasing hormone (Hoechst) were made during the breeding seasons of 1973 and 1974, using 128 mares injected with 1-0 to 4-0 mg of the substance intramuscularly. The mares were placed in one of five groups based on ovarian condition determined by clinical evidence. Some success was obtained in the induction of ovulation in mares with inactive and sub-normally active ovaries and in a small group having cystic ovaries. A large proportion of mares having a mature follicle responded within 48 hr, but others with atretic follicles failed to respond. The u...
