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.
Stabenfeldt GH, Hughes JP, Wheat JD, Evans JW, Kennedy PC, Cupps PT.The effect of hysterectomy on ovarian activity was studied
in four mares. The cyclic secretion pattern of plasma progestins normally
observed in the intact mare was interrupted by hysterectomy. Follicular
activity was observed in all four hysterectomized mares, in spite of pro-
longed luteal activity, with a large number of follicles attaining ovulatory
size without the occurrence of ovulation. Some ovulations were observed
at irregular intervals in two out of four hysterectomized mares in spite
of plasma progestin levels which ranged from 2 to 6 ng/ml. While all
ovulations which occur...
Meijer P.Two cases of tetany in the horse are reported. The two patients were thoroughbreds. One was eight and the other thirteen years old. The mares were in heat and were brought to the service (stud) station to be mated. Both patients were nursing a foal. One was a four-week-old foal and the other was seven weeks old. The calcium level of the serum had dropped in the two patients, to 4.0 mg and 5.4 per ml. respectively. The magnesium level was 1.0 mg and 1.9 mg per 100 ml. respectively. The animals responded satisfactorily to intravenous infusion of calcium borogluconate and magnesium chloride. One ...
Cebulj-Kadunc N, Cestnik V, Kosec M.The onset of puberty and duration of seasonal cyclicity in Lipizzan fillies and young mares have been determined mostly by empirical data, but very little is known about the hormonal changes at puberty and during the seasonal cyclicity in this breed. Objective: To determine the onset of puberty and the course of the cyclicity in young Lipizzan mares from age 1-4 years. Methods: Blood samples were collected twice a month for 2 years from 46 Lipizzan fillies age 1-4 years. Progesterone concentrations, indicating ovarian activity, were measured using an EIA kit. Values above 6.4 nmol/l were taken...
Büchi S, Waelchli RO, Corboz L, Gygax AP, Wälti RJ.In the mare, natural breeding is associated with bacterial contamination of the reproductive tract. The purpose of this study was to examine postcoital bacterial contamination and the resulting inflammatory response of the uterus. Uterine swabs for bacteriological and cytological examination were obtained from 80 mares. Each mare was sampled once between 4 and 69 hours postbreeding. In mares which did not conceive, sampling was repeated at the following estrus. The findings were compared with those obtained prior to breeding and correlated with the breeding outcome. Bacteria were cultured from...
Brockschmidt LD, Loch WE, Sikes JD.An experiment was conducted to test the effect of repeated transcervical (non-surgical) uterine flushing and a prostaglandin analogue (PG) on the estrous cycle of pony mares. Uteri in group A were trancervically flushed for embryos 7 to 9 days post ovulation. In addition, group B mares were given 5 ml of PG by intramuscular injection on the day of flushing. Group C served as controls and were not flushed or given PG but were allowed to cycle normally. All mares (except controls) were bred A.I. every other day during estrus. There was no effect on embryo recovery rate from repeated flushing or ...
Porter MB, Cleaver BD, Peltier M, Robinson G, Thatcher WW, Sharp DC.This study compared equine and ovine LH secretory responses to GnRH treatment. Dioestrous mares and ewes were challenged with continuous GnRH for 15 h. Mares that received constant GnRH (110 micrograms h-1) had sustained LH secretion (P < 0.01), whereas LH concentrations in ewes treated with continuous GnRH (25 micrograms h-1) initially increased, then declined and remained low, suggesting GnRH receptor desensitization or downregulation. In addition, progesterone-primed, ovariectomized mares and ewes were challenged with pulsatile or continuous GnRH for 5 days. Plasma LH concentrations were...
Nitschelm D, Van der Horst CJ.It has been shown that stimulation of the uterus of mares by the daily taking of biopsies can result in the occurrence of oestrous symptoms. This is accompanied by some follicular growth and a progesterone content in the blood often higher than 1 ng/ml. The following observations suggest that this progesterone originates in the uterus and not in the ovaries: (1) no active corpora lutea appeared to be present in the ovaries after ovariectomy, (2) ovariectomized mares showed the same oestrous symptoms in similar experiments and even mating took place, (3) in the uterine biopsies the concentratio...
Ousey JC, Rossdale PD, Cash RS, Worthy K.Multiparous pregnant mares, on two studfarms, were studied following natural challenge with equid herpesvirus-1 (EHV-1). They were divided into three groups according to serum complement fixation titres: Group A (N = 11) were not challenged and delivered normal foals; Group B (N = 13) were challenged but delivered normal foals; Group C (N = 23) were challenged and delivered infected foals which were stillborn or lived for less than 31 h. In Groups A and B mean (+/- s.d.) gestational age at delivery was 343 (+/- 8) and 339 (+/- 8) days respectively, whereas in Group C it was significantly (P le...
Kot K, Tischner M.The aim of the experiment was to determine the effect of a year-to-year prolonged daylength on the patterns of equine reproductive activity and results of embryo recovery. Experiments using Konik Polski mares were conducted over four reproduction seasons. Five mares were exposed to a regimen of artificially prolonged daylength (APD) and another five mares in a control group were kept under conditions of natural daylight. Both the control and experimental groups were examined for appearance of estrus, ovulation and also for the state of their coats. A single stallion was used for breeding all o...
Alexander S, Irvine CH.Mares were bled once daily throughout a cycle, or 3 times daily from the first day of oestrus to the 2nd day after ovulation. LH was measured by heterologous radioimmunoassay and by an in-vitro bioassay based on LH-stimulated testosterone production by mouse Leydig cells. The patterns of bio- and immuno-active LH during the oestrous cycle were similar but not identical, so that in both groups of mares the ratio of biological: immunological (B:I) activity during the LH surge was significantly higher before than after ovulation (P less than 0 . 001). Considerable individual variation in cycle me...
Kikuchi K, Kozai K, Hojo T, Sakatani M, Okuda K, Bai H, Kawahara M, Takahashi M.We investigated the electrical impedance of the reproductive tracts (vagina and uterine endometrial tissues) and the expression of mucus-related genes to identify the stage of the estrous cycle in mares. We first examined vaginal impedance in native Hokkaido mares during their estrous cycle and found no significant differences. However, impedance levels tended to decrease towards ovulation. Furthermore, we investigated the estrous cycle by measuring the electrical impedance of the uterine endometrial tissues obtained from carcasses of mares. We found that impedance levels in the endometrial ti...
El-Maaty AM, Gabr FI.Sixteen Arab lactating mares belonging to Al-Zahraa Arab Horse Stud underwent two ultrasound examinations at 3 weeks interval starting from the day of demonstration of foaling heat. In addition, daily blood samples were collected from parturition until after exhibiting first postpartum estrus (day 11) with daily observation of estrous signs. Both leptin and estradiol hormones were assayed. Mean day of foaling heat was 8.9+/-0.9 day. Most mares came in foaling heat during days 9 and 10 had high conception rate compared to those who came in estrus earlier or later. Estradiol levels were high aft...
Thompson DL, Johnson L.Prolactin concentrations in stallion serum were measured by radioimmunoassay based on antiserum generated against equine prolactin and radioiodinated canine prolactin. Prolactin concentrations in serum collected from 152 stallions at a slaughterhouse were higher (P less than .01) in summer than in winter (5.7 +/- .15 vs 2.0 +/- .17 ng/ml). Moreover, there was an effect of age (P less than .02) in the analysis of variance; there was no interaction between age and season. In general, prolactin concentrations increased with age up to 3 to 5 years. Samples of serum collected from five control and ...
Landim-Alvarenga FC, Alvarenga MA, Seidel GE, Squires EL, Graham JK.Experiments evaluated the ability of follicular fluid (FF), dilauroylphosphatidylcholine (PC12) and the calcium ionophore A23187 (A23187) to induce capacitation in stallion and bull spermatozoa, determined by the ability of the spermatozoa to penetrate zona-free hamster, bovine and equine oocytes. Spermatozoa suspensions were incubated at 37 degrees C in one of the following treatments: 1) a modified Tyrode's medium (BGM3) alone; 2) BGM3 + FF; 3) BGM3 + PC12; 4) BGM3 + FF + PC12; 5) BGM3 + A23187; and 6) BGM3 + FF + A23187. Treated spermatozoa were incubated with zona-free hamster, bovine and ...
Orsolini MF, Meyers SA, Dini P.As the use of assisted reproductive technologies (ART) and in vitro embryo production (IVP) expand in the equine industry, it has become necessary to further our understanding of available semen selection techniques. This segment of our two-section review will focus on the selection of spermatozoa based on quality and sex for equine intracytoplasmic sperm injection (ICSI), as well as current and future developments in sperm sorting technologies. Ultimately, novel methods of semen selection will be assessed based on their efficacy in other species and their relevance and future application towa...
Rodríguez H, Bustos-Obregón E.Epididymal sperm maturation in the stallion was analysed using eight epididymides and deferent ducts from healthy animals. Samples were obtained in June-July and October-November (resting and breeding periods, respectively). Epididymides were divided into head, body and tail. Sperm samples were submitted to a routine seminogram, chromatin decondensation test (Lung, 1972) and sperm velocity determination (Makler, 1980). Results demonstrate that stallion spermatozoa achieve maturation in the transition between the head and body of the epididymis as revealed by chromatin decondensation. Objective...
Kozai K, Hojo T, Takahashi M, Acosta TJ, Nambo Y, Okuda K.Although circulating progesterone (P₄) levels tend to change with the season, little is known about the seasonal changes of P₄ synthesis-related proteins in the corpus luteum (CL) of mares. To examine these changes, seventy-four ovaries containing a CL were collected from Anglo-Norman mares at a local abattoir in Kumamoto, Japan (~N32°), five times during one year. The stages of the CLs were classified as early, mid and regressed by macroscopic observation of the CL and follicles. The mid CL, which had the highest P₄ concentration, was used to evaluate the seasonal changes in P₄ synth...
Ginther OJ, Siddiqui MA, Beg MA.The hypotheses were tested that prostaglandin F2alpha (PGF) travels from the uterus to the ovaries via a systemic route in mares, as opposed to a local route in ruminants, and that one pulse of PGF produces only partial luteolysis. Intravenous (i.v.) and intrauterine (i.u.) infusions of PGF were performed 8 days after ovulation at a constant rate for 2 h. Plasma concentrations of PGF were assessed by assay of 13,14-dihydro-15-keto-PGF2alpha (PGFM). Total doses administered were as follows: 0, 0.05, 0.1, 0.5 and 1.0 mg, i.v., PGF and 0 and 0.5 mg, i.u., PGF (n=4 mares per group). In addition, P...
Leopold S, Samper JC, Curtis E, Buhr MM.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 ...
Plata-Madrid H, Loch WE, Youngquist RS, Thompson DL, Bennett-Wimbush KG, Wilkerson C, Bouchard G, Smith MF, Braun WF, Aveiro JJ.Twenty-two pony mares were used in a project designed to determine the effectiveness of different treatments in controlling FSH, follicular development and synchronization of estrus and ovulation. Mares in Group 1 (n=8) received daily oral altrenogest (0.044 mg/kg); those in Group 2 (n=7) received daily altrenogest (0.044 g/kg) and, during the last 4 days of treatment they received steroid-free follicular fluid, (15 cc) intravenously (I.V.) two times a day; Mares in Group 3 (n=7) received daily intramuscular (I.M.) injections of progesterone (80 mg) and estradiol valerate (7 mg). All treatment...
Günay Uçmak Z, Kurban I, Uçmak M.Endometritis is a major cause of infertility in mares. The aim of this study is to evaluate the preovulatory follicle (POF) vascularization (A mix, A red, A blue), POF diameter, POF wall thickness, and uterine diameters in mares with or without endometritis. Ten healthy mares and 10 mares with endometritis diagnosed by the combination of transrectal palpation, ultrasonographic examination, and cytology brush were enrolled in the study. Data of the groups obtained at 2 days before the ovulation (day -2) were compared with Student's t-test. Correlations of the parameters were determined by the ...
Darenius K.Fifteen mares which had each lost their pregnancies 2 to 8 times during the preceding 6 years were used in a study comprising 1 or 2 breeding seasons for each mare. During the research period all 15 mares conceived and 10 of the mares had normal pregnancies in the 1st experimental year. Five mares resorbed/aborted once or twice during the 1st year. This was followed by a pregnancy that terminated in a live foal. Histopathological examinations of uterine biopsies showed a wide range of histopathological conditions, from absence of changes excessive for the mare's age and parity to the most seve...
Mazan MR.A 30-year-old Morgan-Quarter Horse gelding with hyperadrenocorticism was referred for treatment of a full-thickness tear of the retroperitoneal portion of the rectum. In older horses, the caudal end of the peritoneal space may be farther cranial than is commonly thought. Thus, there is a greater chance that full-thickness rectal tears will involve the retroperitoneal, rather than the peritoneal, portion of the rectum. This horse had a quick recovery and good outcome, despite underlying hyperadrenocorticism that would be expected to impair healing. Although relatively little is known about mana...
Schürmann C, Loose M, Failing K, Wehrend A.The aim of this study was to analyze data concerning history, clinical course, and prognosis of retained fetal membranes in mares. Methods: Patient records of 121 hospitalized mares with retained placenta were evaluated. In 82 cases, additional blood examinations were performed and analyzed. Results: There was no significant correlation between age, parity or course of parturition and retained placenta. Eighty-one mares (66.9 %) were presented solely with retained fetal membranes, 40 mares (33.1 %) had additional diseases at presentation, most commonly injuries of the labia, followed by perine...
Greet TR, Bathe AP.This paper describes the use of a linear stapling device as an aid to unilateral ovariectomy in nine mares with granulosa thecal cell tumours. The intraoperative and postoperative complications are described and follow up details on each case are presented.
Hendrikse J, van der Holst W, Best AP.Examination of 539 ejaculates of stallions of various breeds showed that approximately 60 per cent of the spermatozoa were completely normal morphologically. Of these morphologically normal spermatozoa, 13 per cent were dead. The total proportion of live spermatozoa was 75 per cent, 32 per cent being obviously abnormal (22 per cent of live and 10 per cent of dead spermatozoa). Separated heads (normal as well as abnormal) were significantly more common among dead spermatozoa. Protoplasmic droplets (both at the neck and at the end of the middle piece) were mainly present in live spermatozoa. As ...
Papkoff H, Murthy HM, Roser JF.The tyrosine residues of equine chorionic gonadotropin have been nitrated with tetranitromethane and the resulting effects on the biological and immunological activities of the hormone studied. All of the tyrosine residues in equine chorionic gonadotropin were found to react with tetranitromethane when a 100-fold molar excess of reagent was used or with an 8.6 molar excess in the presence of 5 M guanidine hydrochloride. Complete nitration abolished the biological activities and decreased the immunological activity of the hormone. The nitration of one tyrosine residue resulted in the loss of 70...
Germanà A, Cassata R, Cristarella S, Scirpo A, Muglia U.The three-dimensional architecture of the myosalpinx in the mare was investigated by means of scanning electron microscopy (SEM) after removal of interstitial connective tissue with NaOH digestion. In the extramural portion of the tubo-uterine junction (TUJ), isthmus, and ampulla, the myosalpinx architecture is represented by a unique muscular structure which runs from the mesosalpinx to the base of the inner mucous folds. This unique muscular structure consists mainly of bundles of muscular fibers independent of one another, which show a multiple spatial arrangement and form a complex network...
Sanclemente JL, Ragle CA, Lund CM.A 12-year-old Friesian stallion was examined because of a 1-year history of preputial injury and urination through a urethrocutaneous fistula located at the midbody of the ventral aspect of the penis. Results: Physical examination revealed an opening with a clearly apparent mucocutaneous junction 12 cm from the distal opening of the urethra on the ventral left side of the penis. Endoscopic examination of the distal portion of the urethra confirmed a blind pouch with no communication with the fistula or proximal portion of the urethra. Results: A temporary perineal urethrostomy was performed wi...
Silvia PJ, Fitzgerald BP.An attenuated ovulatory rise in circulating concentrations of LH is characteristically associated with the first seasonal reproductive cycle of horse mares. Unlike ovulations (OV) of subsequent estrous cycles, the first OV of the breeding season (OV1) is not preceded by elevated concentrations of progesterone (PROG). Hence, the ability of pretreatment with PROG to abolish attenuation of LH-secretion associated with OV1 was investigated. Ten nonpregnant anestrous mares were randomly divided into 2 groups; control (C) and treated (T). Per individual, when diameter of the largest follicle was con...
