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.
El-Ghannam F, El-Sawaf S.A study of the estrus cycle of Arabian mares in Egypt gave the following results:
1. The estrus cycle was as short as 12 and as long as 240 days.
2. Cycles considered as normal ranged between 16 and 34 days and were more concentrated in the period 20–26 days.
3. Periods of anestrum caused elongation of the cycles to varying lengths, from double the normal cycle period to four times or more.
4. Seasonal variations in the length of the estrus cycle are discussed.
Douglas RH, Del Campo MR, Ginther OJ.On the day of ovulation (Day 0), 20 pony mares were randomly assigned to one of five groups (4 mares/group) which were given intracarotid arterial (ICA) and intraovarian arterial (IOA) injections on Day 7 as follows: 1) vehicle ICA, vehicle IOA (control); 2) .125 mg PGF2α ICA, vehicle IOA; 3) vehicle ICA, .125 mg PGF2α IOA; 4) .250 mg PGF2α ICA, vehicle IOA; or 5) vehicle ICA, .250 mg PGF2α IOA. Peripheral plasma progesterone and LH concentrations were determined for 0 (pretreatment) and .1, .25, .50, .75, 1, 6, 12, 24, 48, 72 and 96 h posttreatment. The intervals (days) from treatment to ...
Tervit HR.Recent advances in reproductive physiology offer ways for exploiting superior, female cattle and for manipulating physiological events such as parturition. The techniques involved in these advances and their associated hazards are the subject of this review.
Nelson AM.Of 275 mares receiving prostaglandin F2alpha-Tham salt for its luteolytic effect upon the corpus luteum, 231 (84 per cent) exhibited signs of oestrus (range 73-95 per cent). Some mares not exhibiting overt oestrus may, nevertheless, ovulate and post-treatment rectal palpation of mares apparently failing to respond is suggested in these cases. Of 210 mares for which subsequent history was available. 104 (49.5 per cent) became pregnant from breeding at the post-treatment oestrus that immediately followed the induced regression of the corpus luteum (range 42.2-55.5 per cent). Fertility is compara...
Allen WR, Bowen JM, Frank CJ, Jeffcott LB, Rossdale PD.This short review article describes the various techniques currently available for artificial insemination in the horse. The collection and use of raw and extended semen is discussed together with the more recent developments in freezing semen. The expected conception rates with both fresh and frozen semen are quoted. The possible benefits in disease control and stud management are discussed, as well as the difficulties in controlling the use of A.I. from the Breed Registration Authorities point of view.
Garcia MC, Ginther OJ.Six pony mares were ovariectomized (OVX) on day 16 of diestrus during June and July, 1972, to study short term changes in plasma luteinizing hormone (LH) concentrations. Plasma LH was higher (P less than .05) 3 days after OVX (1.76 ng/ml) than the day after OVX (1.01 ng/ml), and a gradual increase occurred over the first 2 weeks. Elevated plasma LH concentrations similar to mid-estrus levels were present from the 2nd to 11th week post-OVX. In another experiment, the same 6 OVX mares were bled once a month from February, 1973, to January, 1974, to study long-term changes in plasma LH in relatio...
Hafs HD.Often in developing hormone assays, hormones that may interfere with the assay by cross-reaction are not available for testing the validity of the assay. For example, horse TSH was unavailable to test for cross-reaction in an LH radioimmunoassay (RIA). The authors devised an indirect means of accomplishing the same goal, and the evidence from the indirect test of cross-reaction was at least as persuasive as a direct test might have been. Other examples are given of experiments where extensive effort was devoted to validation of steroid RIA, but there were substantial quantitative differences i...
Chen CL, Pattison ML, Engleking LR, Gronwall RR.The effect of a subcutaneous injection of estradiol on the secretion of pituitary prolactin in the rat and the relationship between serum estradiol level and luteinizing hormone (LH) secretion in mare were reviewed. In addition, the effect of estradiol injection on LH secretion and the metabolism of [14C] estradiol in intact and bile duct fistulated pony mares were studied. Low (0.1 mug/day/rat) to moderate dose (5 mug/day/rat) of estradiol benzoate injected subcutaneously to mature or immature rats significantly increased pituitary content of prolactin and serum prolactin level five- to tenfo...
Allen WE.14 pregnant Welsh Mountain Pony mares were treated with progesterone in an effort to prevent pregnancy failure induced by administration of human chorionic gonadotropin (GCG). 13 of the 14 mares were treated with progesterone by injection or implant before the 38th day of pregnancy. HCG was given in 3 doses on alternate days at a dose rate of 2000 imc/day. The remaining mare was treated with HCG toward the end of the experiments to demonstrate the abortifacient property of HCG. 3 mares aborted and 1 of these was anovulatory thereafter. Further research is needed to determine the effective prog...
Douglas RH, Ginther OJ.Prostaglandins F were quantitated by radioimmunoassay in uterine venous plasma of anesthetized mares on day 7 of estrus, days 2, 6, 10, 14 or 18 of diestrus and days 10, 14 or 18 of pregnancy. The PGF concentration was greater (P less than .01) at day 14 of diestrus than at all other days studied. The concentrations at days 10 and 18 of diestrus and at days 10, 14 and 18 of pregnancy were greater (P less than .05) than at day 7 of estrus and days 2 and 6 of diestrus. PGF concentrations at days 10 and 14 were greater (P less than .01) for diestrous than for pregnant mares.
Nitschelm D, Van der Horst CJ.The hormonal pattern in the blood of eight mares was studied during the first 5 to 6 weeks of pregnancy; in two of the eight animals early embryonic death was established on D-28 and on D-40, respectively. Progesterone peaks were found in the blood around D-5, D-12 to D-10, and D-17 to D-18. It is suggested that the decrease of the progesterone concentrations in the blood during the intermediate periods is due to the action of oestrogens. During the period from D-18 to about D-34 the concentrations both of progesterone and of pregnenolone were low in the pregnant mares. Thereafter a small incr...
Kieffer NM.Features characteristic of the hereditary syndrome of testicular feminization (tfm) were observed in a 7-year-old Quarter Horse. The horse had female body habitus and male psychosexual behaviour. Gonads located in the abdomen were testes and the uterus and cervix were absent. The vagina was normal in depth but ended as a blind pocket. The sex chromosome composition of testicular fibroblast and leucocyte cultures was XY. Construction of a family pedigree revealed a pattern of hereditary transmission similar to that reported for tfm in other mammalian species.
Thompson DL, Reville-Moroz SI, Derrick DJ, Walker MP.Sixteen intact cyclic mares were treated on the fourth day of estrus and then every other day for a total of six injections with 1) testosterone propionate, 2) dihydrotestosterone (DHT) benzoate, 3) estradiol (E2) benzoate or 4) safflower oil. Mares were given gonadotropin releasing hormone (GnRH) on Day 3 of estrus (pretreatment) and again 24 h after the last steroid or oil injection. Treatment with testosterone propionate resulted in a greater (P less than 0.05) follicle-stimulating hormone (FSH) response to the second injection of GnRH compared with all other treatments. Treatment with DHT ...
Bartmann CP, Stief B, Schoon HA.Transendoscopic thermal preparation techniques like laser- or electrosurgery have proved to be most reliable for minimal invasive intrauterine surgery during operative hysteroscopy in mares. To determine the effect of Nd:YAG laser surgery on the endometrium and the complete uterine wall compared with electrosurgery, standard lesions were obtained by transendoscopic monopolar electrosurgery (loop electrode, cutting blade) and Nd:YAG laser surgery (contact, bare fibre, 25 Watt, exposure time four seconds, non contact, 80 Watt, exposure time four seconds) in five healthy mares on days d 0, 7, 14,...
Sertich PL, Pozor MA, Meyers SA, Brown JS.A 9-year-old Thoroughbred stallion was examined because of breeding dysfunction and possible urethritis. The stallion had good libido and readily obtained an erection, mounted, and intromitted but did not thrust and ejaculate. After mounting the mare, the stallion would squeal and dismount. Endoscopic examination of the urethra and bladder revealed irregular, spiculate yellow crystals (< 1 cm in size) and sabulous deposits; numerous calculi were embedded in the mucosa of the bladder. Because the horse was at the start of a breeding season, the owner would not give permission for general anesth...
Webster WR.A controlled on-farm trial was conducted to evaluate the effectiveness of a commercial gonadotrophin hormone mixture at overcoming a seasonal decrease in fertility in pigs in a sub-tropical environment (summer infertility). The average weaning to oestrus interval of the untreated sows was more than double that of the treated sows and this difference was highly significant. However, fewer of the treated sows farrowed and they produced smaller litters. The improvement in fertility in the treated group achieved by reducing the weaning to oestrus interval was more than cancelled out by an overall ...
Palmer JE.Cardiac arrest in foals is generally secondary to other serious systemic diseases. Although it can often be anticipated, a clear plan is vital to success. Establishing cardiac output through chest compressions is the most important first step. This step should be followed by ventilation, drug therapy, identifying the nonperfusing cardiac rhythm, and following a preplanned treatment algorithm. Birth resuscitation requires special treatment considerations. The clinician should be prepared to perform resuscitation any time a birth is attended.
Klonisch T, Ryan PL, Yamashiro S, Porter DG.To determine the site of relaxin gene expression in equine placentae, a set of degenerate oligonucleotide primers was made according to the published amino acid sequence of the A- and B-chain of equine relaxin (eRXN). Total cellular RNA (tcRNA) from equine placentae at about 120 and 300 days of pregnancy was subjected to reverse transcriptase-polymerase chain reaction (RT-PCR) with use of these primers. A single amplification product of approximately 430 bp was detected in each case by agarose gel electrophoresis. The PCR product was ligated into Bluescript plasmid and sequenced to confirm the...
Marcos R, Ribeiro T, Santos M, Correia-Gomes C, Macedo S, Guimarães T, Blielbernicht M, Caniatti M, Rocha A.Uterine lavage (UL) is a routine diagnostic procedure for endometritis. In UL the fluid is centrifuged and the sediment smeared. Samples prepared in cytocentrifuges, the so-called "cytospins", are useful for evaluating cells in fluids, but never been used in UL. The aim of this study was to assess the usefulness of cytospins after UL, comparing automatic versus manual cytocentrifuges, and to determine their value for the diagnosis of endometritis. The study was divided in two parts. Firstly, UL was performed in 16 mares and a small part of the retrieved fluid was cytocentrifuged in an automati...
Collatos C, Allen D, Chambers J, Henry M.An 8-year-old Arabian stallion had signs of severe tailhead pruritus and slowly progressive loss of tail tone for 3 months. Palpation per rectum and radiography of the sacrocaudal region revealed a transverse, ventrally displaced fracture of the caudal portion of the sacrum. Surgical decompression and tail amputation resulted in complete recovery of athletic and reproductive function. Evidence of cauda equina neuritis was not seen on histologic examination of nerve roots obtained at surgery.
Roth TL, White KL, Thompson DL, Rahmanian S, Horohov DW.The mechanism by which a horse conceptus-derived immunosuppressive factor (HCS) of M(r) > 100,000 inhibits lymphocyte proliferation was investigated. The factor was obtained from the culture supernatants of 20-day-old horse conceptuses; activity, identified by reduced uptake of [3H]thymidine by mitogen-stimulated lymphocytes, was greatest (P < 0.01) in cultures stimulated by mitogen from pokeweed. HCS also suppressed cell proliferation stimulated by phytohaemagglutinin (P 0.05). Data from a fluorescence-activated cell sorter indicated that supplementation with HCS reduced the number of ...
Schnobrich MR, Gordon DL, Scoggin CF, Bradecamp EA, Canisso IF.Urine pooling, as a persistent condition, is a cause of infertility in mares due to endometrial inflammation and sperm toxicity. Identification of urometra can be challenging in mares presenting with the condition intermittently, or when urine flows into the uterus but is undetectable in the vagina. Currently, there are no reported objective methods to confirm the clinical diagnosis of urine contamination in intrauterine-fluid accumulations. Since creatinine is present in high concentrations in urine and does not diffuse across cell membranes, creatinine concentration should be increased in ma...
Goddard PJ, Allen WE.Pressures were recorded monthly at two sites in the vagina of each of five pregnant and five nonpregnant pony mares; pressures in five mares were also recorded weekly after foaling. The developing pregnancy did not influence pressure, and after foaling the integrity of the seal formed by the caudal reproductive tract was rapidly restored.
Watson ED, Stokes CR.Immunoglobulins A, G and M were localised by immunoperoxidase staining of endometrial sections from ovariectomised mares. Treatment with progesterone or oestradiol-17 beta did not significantly affect numbers of cells secreting any of the isotypes. Mares with persistent endometritis did not have significantly greater numbers of endometrial plasma cells than genitally-normal mares.
Heiskanen ML, Huhtinen M, Pirhonen A, Mäenpää PH.Semen from 3 stallions was extended using 2 methods (Kenney extender and a modified Kenney extender), slowly cooled, and stored for 41 +/- 6 (s.d.) h before insemination. An insemination dose (40 ml) contained 1.5-2 billion spermatozoa. In the experiment, 26 mares were inseminated in 30 cycles. The pregnancy rate per cycle obtained with sperm stored in the Kenney extender was 87% (n = 15). When the semen was extended with the modified extender, centrifuged and stored, the pregnancy rate was 60% (n = 15). Inseminations were done every other day until ovulation was detected. If a mare ovulated m...
Meinecke B.The present study comprises 31 mares, that showed a permanent unilateral enlargement of the ovary. In 29 patients the ovary in question was removed by a flanc laparotomy in the standing animal. In the histopathologic examination a granulosa cell tumor was diagnosed in 23 cases, a fibroma twice and a teratoma, hematoma, leiomyoma and a cystic ovary each once. Due to the endocrine activity of the granulosa cell tumor, the clinical picture was characterized by changed behaviour and atrophy of the contralateral ovary. Clinically the ovarial blastomas (teratoma, leiomyoma, fibroma) could not be dif...
Floris B, Bini PP, Nuvole P.The blood testosterone changes in three Giara stallions, average age 8 years old and average weight 183 Kgs, were checked weekly for a year using a radioimmunological method. The horses showed a highly seasonal hormonal activity concentrated in the first half of the year (winter and spring). In the second half of the year (summer and fall) the stallions showed low levels of testosterone. The highest level of the androgen hormone occurred in April, the lowest in October. The absolute levels of this hormone agreed substantially with the relative literature.
Tomasgard G, Benjaminsen E.Sixtyfour mares were examined 3 and 6 weeks after mating. Progesterone was measured in 22 mares 3 weeks after mating in order to see if this could be of any help in the oestrous diagnosis. None of the pregnant mares had plasma progesterone below 2 ng/ml. Pregnant mares that did not show oestrus had higher levels of plasma progesterone than pregnant mares showing signs of oestrus 3 weeks after mating. Clinical findings in pregnant and nonpregnant mares 3 weeks after mating is compared, and oestrus in pregnant mares is discussed.
Hinrichs K, Frazer GS, deGannes RV, Richardson DW, Kenney RM.Serous cystadenoma was diagnosed by histologic examination of a large ovary removed from a 16-year-old Thoroughbred mare with normal estrous cycles. Palpation and ultrasound examination per rectum had revealed an excessive number of follicles in the right ovary. The ovulation fossa was palpable on the right ovary, and the left ovary appeared to have normal activity. Plasma testosterone values were high at the time of examination (0.15 ng/ml), but decreased to normal values (0.09 ng/ml) after removal of the cystadenoma.
Derar R, Haramaki S, Hoque S, Hashizume T, Osawa T, Taya K, Watanabe G, Miyake Y.To elucidate the physiological role of insulin-like growth factor-I (IGF-I) during early pregnancy in mares, number of ovarian follicles was monitored ultrasonically during different stages of the first trimester of pregnancy in 36 thoroughbred mares. From 9 of 36 mares, blood samples were collected weekly from the mating day till the end of the first trimester of pregnancy and plasma IGF-I profiles were examined with other hormones, like follicle stimulating hormone (FSH), luteinizing hormone (LH), ir-inhibin, progesterone and estradiol-17beta. Plasma IGF-I level fluctuated throughout the stu...
Freestone JF, Paccamonti DL, Eilts BE, McClure JJ, Swiderski CE, Causey RC.A 5-year-old stallion was referred because of signs of abdominal pain. During the initial examination, signs of pain were elicited when the right seminal vesicle was palpated per rectum. Signs of pain were also elicited during sexual arousal and attempts at semen collection. The right seminal vesicle was subsequently determined to be abnormal by ultrasonographic and endoscopic examination. The stallion was treated with trimethoprim/sulfamethoxazole for 6 weeks. Five months later, there had been no recurrence of the condition.
Cohen ND, Donahue JG, Carey VJ, Seahorn JL, Piercy D, Donahoe JK, Williams DM, Brown SE, Riddle TW.To identify factors associated with abortions during early gestation classified as mare reproductive loss syndrome (MRLS). Methods: Case-control study. Methods: 324 broodmares from 43 farms in central Kentucky, including 121 mares from 25 farms that had early-term abortions (ETAs) associated with MRLS (case horses), 120 mares from the same farms but that did not abort, and 83 mares from 18 farms that were not severely Impacted by MRLS. Methods: Farm managers were interviewed to obtain data on various management practices and environmental exposures for the mares. Data for case and control hors...
Tischner M, Bielański A.Observations were made on 14 mares which were non-surgically flushed on one or more occasions for recovery of embryos on Days 7-9 after ovulation. Flushing alone shortened the oestrous cycle by about 2.7 days but increased the number of mares failing to ovulate. Flushing followed by an injection of a prostaglandin analogue shortened the cycle by about 4.5 days and hence increased the frequency of ovulations. From a total of 70 flushings performed, 27 embryos were recovered and of 12 mares inseminated during the first oestrus after embryo collection, 6 conceived and foaled. The other 7 mares we...
Pace-Owens S.Gamete intrafallopian transfer (GIFT), developed in 1984, was the result of further studies on in vitro fertilization (IVF). Since that time many nurses have worked in settings near in vitro fertilization centers and, therefore, have a basic understanding of the technology. An overview is given of the GIFT procedure to prepare nurses to advise and refer couples who may qualify for GIFT and to highlight the shift in the fertility program nurse coordinator's functions toward the positions of administrator and consultant.
Duguma A, Lemma A, Hibste A.Equine reproduction is unique by having long behavioral estrus and differences in time of breeding between breeds and individuals of mares. An experimental study was conducted at the Balderas Sport Horses and Recreational Center, Addis Ababa, Ethiopia, from January to June, 2018, to evaluate conception rate to frozen semen in local and exotic crossbreed mares. Mares were teased to characterize estrus behavior and examined by ultrasound in determining imminent ovulation. Inseminations were done post ovulation within an average of 6-9 h using frozen-thawed semen. The overall conception rate to ...
McKellar GM, Collins AP.The surgical correction of midfacial deformities of the horse have rarely been undertaken. This article describes the successful management of a submucous cleft of the maxilla in a young colt. Details of the operative and perioperative medical and surgical management are described. The horse, now 5 years of age, has sired eight normal progeny.
Hohenhaus MU, Lehmann B.Ultrasonography is a good means of monitoring follicular development in the mare and allows objective observation and measurement of follicular growth as well as identification of corpora lutea and hematoma in the ovary. The significance of ultrasonography in this field lies in the specific anatomical structure of the mare's ovary and the different phenomena preceding and accompanying ovulation, which are described in this paper. The last part deals with the handling and use of ultrasonography.
Braun U, Förster M, Schams D.A case of intersexuality in an arabo-haflinger horse is described. The external genitalia consisted of mammary gland, vulva and hypertrophic clitoris; the inner genitalia of rudimental testes. The sexual behaviour was typically male-like. The chromosome analysis showed the female karyotype 64,XX. The presence of testes in a genetically female animal is explained by translocation of an Y-chromosome fragment bearing the gene for the H-Y-antigen.
Weiblen R, Rabuske M, Rebelatto MC, Nobre VM, Canabarro TF.We report an outbreak of abortion due to equine herpesvirus (EHV) in 5 mares between 9 and 11 months of gestation, from a herd of 22 Thoroughbred mares. Equine herpesvirus was isolated from extracts of the liver, spleen and thymus but not from the lungs of a 9-month fetus grown in Rabbit Kidney (RK13) cells. The virus was identified by electron microscopy, where virus particles could be seen in the nucleus of infected cells, and by the fluorescent antibody technique with polyclonal antibodies against the whole virus. Anamnesis, necropsy, histopathology, bacteriology, and virology data suggest ...
Pozor MA, McCarrel TM, Perez Jimenez EE, Macpherson ML, Kelleman AA, Shelton KE.An 18-year-old Appaloosa stallion presented with a history of ejaculatory dysfunction, which had recently progressed to an inability to ejaculate (anejaculation). Transrectal ultrasound evaluation revealed the presence of a prominent midline cyst of the colliculus seminalis, which was compressing the most terminal parts of the deferent ducts. Both ducts were enlarged and filled with hyperechoic content. The stallion was diagnosed with a complete occlusion of the deferent ducts because of the compression from the midline cyst of the colliculus seminalis. To date, there are no established treatm...
Benoit E, Garnier F, Courtot D, Delatour P.Antiserum has been raised in rabbits treated with a 19 nor testosterone-hemisuccinate-bovine-serum-albumin conjugate and used for the development of a specific RIA of plasma 19 nor testosterone. Plasma samples are drawn from testicular and jugular veins of stallions during castration under general anesthesia. Results demonstrate a testicular secretion of 19 nor testosterone and a stress inhibition of this secretion correlatively with stress inhibition of testosterone secretion.
