Pregnancy in horses, or equine gestation, is a physiological process that involves the development of a foal within the mare over approximately 11 months. This period is characterized by distinct stages, including fertilization, embryonic development, and fetal growth. Throughout gestation, mares undergo various physiological and hormonal changes to support the developing fetus. Monitoring pregnancy in horses involves assessing fetal health and mare well-being through veterinary examinations and diagnostic tools such as ultrasound. This page compiles peer-reviewed research studies and scholarly articles that explore the physiological processes, management practices, and health considerations associated with equine pregnancy.
Vandeplassche M, Podliachouk L, Beaud R.A study has been made of 44 cases of twin pregnancy in mares. The fetuses, foals, fetal membranes and blood groups of parents and foals were examined in order to determine the incidence of chorio-vascular anastomosis, blood chimaerism and freemartinism. All of the twins proved to be dizygotic and 33 of the 34 pregnancies were bicornual. Fusion of the chorion was seen in 14 of 22 placentas and macroscopic choriovascular bridges were observed in five of these, although blood chimaerism was diagnosed in 11 of 25 cases (44 per cent) examined. This would indicate a high incidence of microchoriovasc...
Rau J, Tiedemann D, Sielhorst J, Tönissen A, Burger D, Martinsson G, Rohn K, Oldenhof H, Sieme H.Transvaginal ultrasound-guided aspiration (TUA) is a procedure which can be used for the reduction of twins post-fixation in the mare. The aim of this study was to evaluate the effect of the age of mares and the day of gestation on the outcome of TUA treatment. Methods: In 88 mares, diagnosed pregnant with twins, TUA of the yolk sac or allantoic fluid was performed between day 30 and 62 of gestation. Mares were aged 3-22 years. Ultrasonographic examination for a viable singleton pregnancy was performed by referring veterinarians 5-7 days and 4 weeks after TUA. Based on reported findings, effec...
Plotka ED, Vevea DN, Eagle TC, Tester JR, Siniff DB.Homogeneous Silastic rods containing ethinylestradiol (EE) (1.5 or 4 g), estradiol-17 beta (E) (4 g) or progesterone (P) (6 g) were implanted into feral mares (Equus caballus) between 4- and 10-yr-old. Six treatment groups (greater than or equal to 10 mares/group) of non-pregnant mares received 36 g P and 12 g E (P+E), 36 g P and 8 g EE (P+HEE), 1.5 g EE (LEE), 3 g EE (MEE, 8 g EE (HEE) or control-implanted mares (CI). CI received implants containing no steroid. Two groups of pregnant mares received P+HEE or HEE. Stallions were placed with the mares 15 to 26 mo after implanting. Blood was coll...
Pope NS, Sargent GF, Wiseman BS, Kesler DJ.Frequent blood samples were collected from 8 pony mares before, during and after labour, parturition and placental expulsion and assayed for progesterone, oestradiol, androstenedione and LH concentrations by radioimmunoassay. A significant (P less than 0.05) decrease in progesterone, oestradiol and in the progesterone:oestradiol ratio was not detected until 0.5 h after foaling. Androstenedione concentrations rose before and peaked at parturition and then declined. A significant (P less than 0.05) rise in LH was detected 0.5 h after parturition. This LH peak was not detected in one mare and she...
Griffin PG, Ginther OJ.Fetal activity and mobility and changes in diameter of the allantoic fluid compartment in the uterine horns were studied in mares between days 69 and 81 of pregnancy by use of transrectal ultrasonography (n = 12) and transcervical videoendoscopy (n = 8). The insertion tube of the videoendoscope was positioned within the allantoic sac to permit viewing of the fetus and entrance to each uterine horn. Each uterine horn was divided ultrasonographically into 3 segments of equal length, and the horns were designated on the basis of side of umbilical attachment (cord vs noncord horns). The diameter o...
Cohen ND, Carey VJ, Donahue JG, Seahorn JL, Brown SE, Riddle TW.To characterize the temporality of dates of breeding and abortion classified as mare reproductive loss syndrome (MRLS) among mares with abortions during early gestation. Methods: 2,314 mares confirmed pregnant at approximately 28 days after breeding from 36 farms in central Kentucky, including 515 mares that had early-term abortions. Methods: Farm veterinarians and managers were interviewed to obtain data for each mare that was known to be pregnant to determine pregnancy status, breeding date, last date known to be pregnant, and date of abortion. Results: Mares bred prior to April 1, 2001, app...
Ingarden J, Dubiel A, Rauluszkiewicz S.This study investigated the effect of a beta blocker on parturition, fetal membrane retention and subsequent fertility in mares. The animals were divided into an experimental group (150 mares treated during second stage labour with propranolol [50 mg i.v.]) and a control group (180 mares with no treatment). Administration of propranolol was associated with a significant decrease in time of expulsion of fetal membranes, and an increase in both exhibition of foal heat and pregnancy rates at this heat.
Madej A, Kindahl H, Nydahl C, Edqvist LE, Stewart DR.Two mares received PGF-2 alpha twice daily until abortion and 2 mares received a combined treatment with oestradiol benzoate and oxytocin. The mares were about 150 days pregnant. The PG-treated animals aborted after 37 and 61 h, respectively, and the fetuses were expelled in intact fetal membranes. The other 2 mares aborted 13 and 27 h after the first oxytocin injection, respectively, and showed strong uterine contractions and expelled the fetuses in disrupted fetal membranes. Concentrations of 15-ketodihydro-PGF-2 alpha increased both after PG and oxytocin injections and in association with t...
Day WE, Bowen JA, Barhoumi R, Bazer FW, Burghardt RC.This investigation examines the relationship between implantation strategy and gap junction protein expression in uterine endometrium. The pattern of gap junction and connexin protein expression was analyzed in porcine and equine endometrium from cycling and pregnant animals using electron microscopy and immunocytochemistry. Functional analysis of cell-cell communication was also monitored by laser cytometry in primary cultures of endometrial epithelial cells. Gap junctions were detected in endometrial stroma of cycling and pregnant animals, which was correlated with immunoreactive Cx43 within...
Bhavnani BR, Woolever CA.A mixture of [4,8,12-14C]farnesyl pyrophosphate and [3H]dehydroepiandrosterone was injected into a horse fetus im during laparotomy, after which maternal urine was collected for 6 days. Steroid conjugates in the urine were extracted with Amberlite XAD-2 resin, hydrolyzed, and separated into phenolic and neutral fractions. Estrone, 17 alpha-estradiol, equilin [3-hydroxy-1,3,5(10),7-estratetraen-17-one], and 17 alpha-dihydroequilin [1,3,4(10),7-estratetraene-3,17 alpha-diol] were isolated from the phenolic fraction and their radiochemical purities were established. Only estrone and 17 alpha-estr...
Webel SK, Squires EL.The clinical effectiveness of the synthetic progestagen, altrenogest, was evaluated in field trials with 449 mares during the 1980 breeding season. An oral dose of 27 mg altrenogest was administered daily for 15 days. In the first trial treated mares were compared with controls, and in the second trial the effectiveness of treatment for prolonged or erratic spring oestrus was evaluated. Oestrus was suppressed in 94% of the treated mares in the first trial. The post-treatment response was related to the stage during the transition from winter anoestrus to the spring breeding season and degree o...
Gudev Kh, Kovachev G.Alantoamnion vascularization was studied on clarified preparations from three mares in advanced pregnancy. Two large blood vessels (artery and vein) beginning from the umbilical vessels were found in the alantoamnion wall. Numerous anastomoses were observed at the passage between the arterial and the vein section. The large arteries had a thick, jely-like vascular wall and snake-like folded lumen. In separate sections of the alantoamnion wall a well developed capillary net was observed consisting of individual particles, polygonal in shape. Vast avascular zones surrounded by numerous vascular ...
Bruemmer JE, Brady HA, Blanchard TL.The effects of a single or double regimen of exogenous progesterone and estradiol-17beta (P/E, total dose 300 mg P/20 mg E) were investigated in 50 postparturient Quarter Horse mares. In Trial 1, at 1 and 24 h after foaling, mares were injected with progesterone (150 mg) and estradiol-17beta (10 mg) (n = 7) or 0.9% NaCl (control, n = 13). In Trial 2, within 12 h after foaling, mares were injected with progesterone (300 mg) and estradiol-17beta (20 mg) (n = 13) or 0.9% NaCl (control, n = 17). Mares were examined daily by palpation per rectum and transrectal ultrasonography to determine the day ...
Daels PF, Chang GC, Hansen B, Mohammed HO.We have characterized the testosterone secretion pattern during the first 80 d of pregnancy in mares and determined the sources that contribute to circulating testosterone levels during this period. Ten untreated, pregnant mares (Group 1), 10 altrenogest-treated, pregnant mares (Group 2), and 10 altrenogest-treated, pregnant mares in which the CL was eliminated by administration of PGF-2alpha on Day 16 (Group 3) were used in this study. Complete luteolysis occurred following PGF-2alpha administration in all mares in Group 3. Six of the 10 mares in Group 3 did not have an active CL until after ...
Dehennin L, Petit E, Bonnaire Y, Bruyas JF, Le Bizec B, Plou P.Rules of horse racing stipulate that pregnant mares may compete under definite conditions of date, because early pregnant status may be misused for the sake of enhancing physical performance by putative anabolic steroid action. Screening for pregnancy is generally performed by plasma equine gonadotrophin (eCG) immunoassay, which covers the period between Days 40 and 120. In common screening for urinary anabolic steroids performed by gas chromatography-mass spectrometry, inclusion of two complementary criteria, i.e. the evaluation of total conjugates of 5(10)-estrene-3beta,17alpha-diol (EED) an...
Wynn MAA, Ball BA, Legacki E, Conley A, Loux S, May J, Esteller-Vico A, Stanley S, Scoggin K, Squires E, Troedsson M.In the latter half of gestation in the mare, progesterone concentrations decline to near undetectable levels while other 5α-reduced pregnanes are elevated. Of these, 5α-dihydroprogesterone and allopregnanolone have been reported to have important roles in either pregnancy maintenance or fetal quiescence. During this time, the placenta is necessary for pregnane metabolism, with the enzyme 5α-reductase being required for the conversion of progesterone to 5α-dihydroprogesterone. The objectives of this study were to assess the effects of a 5α-reductase inhibitor, dutasteride on pregnane metab...
Meier HP, Gertsch U, Kohler S.Twin pregnancies are a serious problem in stud medicine as they terminate in most cases in abortion, stillbirth or the delivery of dead or weak and deformed foals. In recent years, the introduction of sonography has greatly improved the management of mares with twin conceptuses, in particular monitoring the phenomenon of spontaneous embryo reduction to a single vesicle. This allows supervision of pregnancy with relatively little expenditure and loss of time. We document the spontaneous reduction to single vesicles of unilateral twin pregnancies in a draught- and a warmblood-mare. In both mares...
Jedruch J, Gajewski Z, Kuussaari J.The effect of detomidine on the electrical activity of the uterus was studied during the last trimester of pregnancy in 6 mares. The effect was observed in 3-5 min after the i.m. injection and it lasted for 50-70 min. 20 and 40 micrograms/kg b.w. doses of detomidine decreased the myometrial electrical activity, whereas 60 micrograms/kg dose did not have any effect on the activity. The results suggested that 20, 40 and 60 micrograms/kg b.w. doses of detomidine can be administered to mares during the last trimester of pregnancy without the risk of abortion induced by increased uterine electrical...
Lowe JE, Foote RH, Baldwin BH, Hillman RB, Kallfelz FA.Three Quarter-horse mares were thyroidectomized at about 1.5 years of age. Three similar intact mares served as controls. The study continued through two breeding seasons. The thyroidectomized mares were lethargic, rear limbs were oedematous and hair coats were coarse. They displayed a tranquil oestrous behaviour when exposed to a stallion and were only mildly antagonistic when not in oestrus. Length of oestrous cycles varied but most often they were 19-24 days long. Duration of oestrus (mean +/- s.e.m.) for the control and thyroidectomized mares was 12.9 +/- 2.9 and 11.7 +/- 2.2 days respecti...
Gilbert RO, Marlow CH.Records of 1,009 pregnancies in 574 foaling, barren and maiden Thoroughbred mares on a single stud farm, over a period of 12 years were examined. The farm is situated in the eastern Cape Province of South Africa, at an elevation of 1,800 m, and in an area of climatic extremes. Records of 604 pregnancies in 249 foaling Thoroughbred mares were examined. For these purposes, those pregnancies in which a mare conceived in the same breeding season during which she had foaled were considered as pregnancies in foaling mares. Pregnancy was confirmed by rectal palpation by a single experienced practitio...
Donatsch L, Friker B, Sieme H, Kaeser R, Burger D.A potential source of fertility loss in mares is oviductal dysfunction, potentially caused by masses or debris in the lumen, that may prevent either sperm from reaching the fertilization site or the embryo from reaching the uterus. Recently a novel therapeutic method leading to increased pregnancy results was described by infusing misoprostol, a synthetic prostaglandin E, in the uterus of mares with unexplained fertility problems. In this study, we aimed, after examining the compatibility of misoprostol with semen, to evaluate the pregnancy rate after routine preovulatory deep uterine horn app...
Urquieta B, Durán MC, Coloma I, Parraguez VH.Our aim was to compare Corpus luteum (CL) development and blood plasma concentration of progesterone ([P4]) in thoroughbred mares after spontaneous ( Methods: C) or human chorionic gonadotrophin (hCG)-induced ovulation. Lactating mares (C=12; hCG=21) were daily teased and mated during second oestrus post-partum. Treated mares received 2500 IU hCG i.v. at first day of behavioural oestrus when dominant follicular size was >35, or=45 mm. Dominant follicle before ovulation, CL and gestational sac were measured by ultrasound and [P4] by radioimmunoassay (RIA). Blood sampling and ultrasound CL ex...
Antczak DF.A new polymorphic locus of the horse which has several unusual properties is described. The suggested name for the locus is ELY-2. The gene product of one allele at this locus, designated ELY-2.1, has been identified with antisera raised as a result of pregnancy. Antibody to ELY-2.1 was first detected on day 55 after conception in the serum of a mare in first pregnancy. This early onset of antibody is similar to that seen for antibody to ELA antigens, and suggests that the source of the antigenic stimulus may be the tissue of the equine endometrial cups. The antisera identifying ELY-2.1 are cy...
Woods GL, Ginther OJ.The ability of a pituitary extract to induce ovulation and the effect of multiple ovulations on pregnancy rate and incidence of multiple fetuses were studied in seasonally anovulatory mares. The extract induced ovulation in 95% of mares having a greater than or equal to 25 mm follicle at the onset of treatment and in 64% the ovulations were multiple. The extract was less effective when the largest initial follicle was less than 25 mm. Approximately 50% of the treated mares that ovulated did not become pregnant or enter prolonged dioestrus before returning to an anovulatory condition. In treate...
Scherzer J, Davis C, Hurley DJ.The major difficulty in providing the benefits of embryo cryopreservation for equine agriculture is the mismatch between the optimal embryo age for collection from the mare (7-8 days after ovulation was detected) and the optimal age for freezing under current methods (6.5 days after ovulation). To overcome this limitation, we tested a method to enhance penetration of cryopreservative across the capsule and trophoblast of day 7 and 8 embryos combined with rapid freezing by vitrification. Six small embryos (<300 μm in diameter) were collected on day 6-7 after ovulation and twelve larger embryos...
Gastal MO, Gastal EL, Torres CA, Ginther OJ.The effects of oxytocin, prostaglandin F2 alpha (PGF2 alpha), and clenbuterol on uterine contractility and tone during anestrus and diestrus, and during mobility and postfixation of the embryonic vesicle were studied in 51 pony mares. Contractility was assessed by scoring real-time ultrasound images, and tone was assessed by transrectal digital compression. Scoring was done by an operator who had no knowledge of treatment assignments. In anovulatory mares primed with progesterone for 16 d, oxytocin did not significantly alter contractility but did stimulate an increase in tone, whereas clenbut...
Enders AC, Liu IK.The free allantois and allantochorion of conceptuses from 17 mares between 20 and 90 days of gestation were examined to determine the manner in which the associated mesodermal derivatives differentiated. It was found that a robust basement membrane developed under the allantoic endoderm, and that this basement membrane was partially isolated from the vascular layer of the allantois by a mesothelial layer and an exocelom-like space. The exocelom-like space persisted until approximately the stage of villous formation, and remnants of the space persisted over larger allantoic vessels even later. ...
Saint-Dizier M, Chopineau M, Dupont J, Combarnous Y.The full-length equine luteinizing hormone/chorionic gonadotropin (LH/CG) receptor (eLH/CG-RA) cDNA and two alternatively spliced isoforms (eLH/CG-RB,C) were isolated from luteal tissue and characterized using a combination of reverse transcription-polymerase chain reaction (RT-PCR) and 5'-rapid amplification of cDNA ends. The 680-amino acid full sequence of eLH/CG-RA displayed 87-92% homology with other mammalian LH/CG-Rs. The eLH/CG-RB and eLH/CG-RC cDNA isoforms were truncated from the 3'-end of exon X: eLH/CG-RB spliced out of frame into the last exon whereas eLH/CG-RC contained an in-fram...
Thompson DL, Reville SI, Derrick DJ.Five mature Quarterhorse mares were bled every 30 min for 25 h on day 50 of pregnancy to determine the short-term mode of secretion of equine chorionic gonadotropin (eCG). Three other mares with persistent endometrial cups after abortion were administered gonadotropin releasing hormone (GnRH; 1.0 mug/kg of body weight) and were bled immediately prior to and at 15, 30, 45, 60, 90, 120, 180 and 240 min after GnRH. Concentrations of eCG in plasma of pregnant mares were constant over the 24-h period; the variation of each mare's individual values was no greater (P>.05) than the predicted random...
Kalpokas I, Martínez MN, Cavestany D, Perdigón F, Mattos RC, Meikle A.We investigated the early effects of the equine embryo on maternal serum concentrations of insulin-like growth factor 1 (IGF1), leptin and adiponectin, uterine immune cells and genes and proteins related to embryo development and the maintenance of pregnancy. Ipsilateral endometrial expression was assessed on Days 7 and 13 after ovulation for the following transcripts: oestrogen receptor ERα (ESR1), progesterone receptor (PGR), progestin and adipoQ receptor family member 5 (PAQR5), oxytocin receptor (OXTR), prostaglandin-endoperoxide synthase 2 (PTGS2), raf-1 proto-oncogene serine/threonine k...
García-Tamayo J.Clinical findings on Venezuelan Equine Encephalitis virus infection and the teratogenic effects of several Togaviruses are described. Similarities between the intrauterine alterations induced by Venezuelan Equine Encephalitis virus and rubella virus are pointed out. Findings described by Wenger in 1967 were those of massive cerebral necrosis in fetuses of women presumably suffering of encephalitis and they are commented along with the development of an animal experimental model at the end of 1970-1980. Pathogenesis of the intrauterine infection seemed to be related to changes in the placental ...
