Topic:Gestation
Gestation in horses refers to the period during which a mare carries a developing fetus, typically lasting around 11 months, or approximately 340 days. This process involves a series of physiological and hormonal changes that support fetal development and prepare the mare for parturition. Key stages of equine gestation include fertilization, embryonic development, and fetal growth, each characterized by specific developmental milestones. Monitoring the health and progress of gestation is essential for ensuring the well-being of both the mare and the foal. This page compiles peer-reviewed research studies and scholarly articles that explore the various aspects of equine gestation, including hormonal regulation, fetal development, and factors influencing gestational length and outcomes.
Effect of Salmonella typhimurium endotoxin on PGF-2 alpha release and fetal death in the mare. The infusion of Salmonella typhimurium endotoxin into pregnant mares resulted in a biphasic release pattern of PGF-2 alpha as determined by 15-keto-13,14-dihydro-PGF-2 alpha concentrations. The initial phase of 1 h duration was followed by accentuated release by 2 h after infusion; concentrations reached basal levels by 6 h. In 7 mares at 23, 26, 29, 33, 36, 53 and 55 days of gestation, fetal death occurred between 36 and 120 h after infusion; 12 mares at 46, 51, 56, 59, 65, 71, 73, 85, 103, 138, 283 and 318 days of gestation did not abort after endotoxin infusion. Luteal activity was compromi...
Changes in maternal hormone concentrations associated with induction of fetal death at day 45 of gestation in mares. Pregnant Standardbred mares were allocated to 2 groups. On Day 45 of gestation, 20-45 ml saline (240 g NaCl/l) were injected into the fetal sacs of 10 mares, and the other 10 mares were given sham treatment. Post-operative plasma oestrone sulphate concentrations were lower (P less than 0.01) on Days 48-55 in saline-treated mares than in sham-treated mares. Mean plasma progesterone profiles were similar in the two groups of mares, although post-operative luteolysis occurred in 4 saline-treated mares. There was no difference in plasma CG profiles between the 2 groups, except that CG concentratio...
The effects of four levels of endophyte-infected fescue seed in the diet of pregnant pony mares. Mean weight of 20 Quarter Horse placentas on a wet basis was 3.27 +/- 0.17 kg. These placentas contained mean dry fat-free tissue, DNA, RNA and collagen weights of 411 +/- 24 g, 11.2 +/- 0.6 g, 12.4 +/- 0.7 g and 210 +/- 15 g, respectively. In Ponies and Quarter Horses, there was a trend towards a decrease in these 4 values as gestation length increased. Analysis of placentas of Ponies fed different amounts of endophyte fungus-infected fescue seed showed that weight of dry fat-free tissue increased with increasing percentages of fescue seed in the diet. Diets containing fescue seed resulted in...
Plasma concentrations of progestagens, oestrone sulphate and prolactin in pregnant mares subjected to natural challenge with equid herpesvirus-1. 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...
Fertility of pasture bred mares in synchronized oestrus. Oestrus was synchronized in 220, 300 and 272 mares in 1983, 1984 and 1985 respectively. Mares were given two injections of 250 micrograms fenprostalene 15 days apart except in 1983 and 1984 when 56 and 53 of the synchronized mares were given 1-10 daily injections of 150 mg progesterone and 10 mg oestradiol-17 beta to delay and synchronize post-partum oestrus. At 2 days after the second PG injection or 7 days after the last progesterone + oestradiol treatment, mares were divided into groups of 15-21, and each group was placed in a separate pasture with a stallion for 7 weeks. Pregnancy rates we...
Differentiation molecules of the equine trophoblast. Monoclonal antibodies raised against horse placenta were tested using an indirect immunoperoxidase-labelling technique for reactivity with a panel of tissues from adult horses and conceptuses of various gestational ages. The pattern of reactivity of 4 of the antibodies (F67.1, F71.3, F71.7, F71.14) on trophoblastic tissues described unique antigenic phenotypes for the non-invasive trophoblast of the allantochorion, the invasive trophoblast of the chorionic girdle, and the mature endometrial cup cells, which are derived from the chorionic girdle. Two of the monoclonal antibodies (F67.1 and F71....
Genetic and temporal variation in serum concentrations and biological activity of horse chorionic gonadotrophin. The variation in the quantity of circulating chorionic gonadotrophin (CG) and its follicle-stimulating hormone (FSH) and luteinizing hormone (LH) activity in rodent bioassay systems was investigated. A portion of the variability in total CG could be attributed to the stallion that sired the pregnancy and it was possible to select sires and mares to increase CG production. It was further demonstrated that FSH activity per unit of CG was greater at Days 71 and 104 of gestation than at Day 39. LH activity per unit of CG varied with the sire, but no effect of day of gestation could be shown. It wa...
Effect of altrenogest on pregnancy maintenance in unsynchronized equine embryo recipients. Non-surgical embryo recovery attempts were done on Day 7 after ovulation. Embryo recovery rate from mares of varied reproductive histories was 57% (38/67). Non-surgical transfer of these embryos into altrenogest-treated recipient mares that ovulated between 3 days before and 3 days after the donor resulted in a 30-day pregnancy rate of 77% (10/13). Transfer of embryos into altrenogest-treated recipients that ovulated between 4 days before and 6 days after the donor resulted in an overall pregnancy rate of 64% (16/25) at Day 30 of gestation. No recipients that were in oestrus at the start of tr...
Effects of inhibiting 3 beta-hydroxysteroid dehydrogenase on plasma progesterone and other steroids in the pregnant mare near term. Epostane, a competitive inhibitor of 3 beta-HSD was administered intravenously to a pregnant mare between 292 and 330 days of gestation at doses of 1-3 mg/kg/min. Plasma progesterone concentrations fell rapidly during epostane infusion in both the artery and uterine vein and remained significantly depressed for 4-5 h after the start of infusion. The venous arterial (V-A) plasma concentration difference in progesterone across the uterus also decreased significantly in response to epostane infusion. There were no significant changes in plasma progesterone or in the V-A concentration difference i...
Motility and fertility of equine spermatozoa extended in bovine serum albumin and sucrose. Inclusion of either 1 or 3% (w/v) bovine serum albumin (BSA) in 8.6, 10, or 12% sucrose enhanced the maintenance of equine sperm motility in vitro at 38 degrees C for 8 h. There was a trend toward higher percent motile spermatozoa (PMS) at 16 and 24 h of incubation in semen samples containing BSA than in those that did not. The highest concentration of sucrose (12%) was slightly less effective in supporting PMS than either of the lower concentrations. However, sucrose concentrations had no apparent effect on rate of forward movement (RFM) of spermatozoa. Pregnancy and foaling rates were simila...
Behavior and viability of the premature neonatal foal after induced parturition. Parturition was induced in 2 groups of mares, less than 300 (n = 49) and 300 to 320 days gestation (n = 31), by the administration of prostaglandin F2 alpha or fluprostenol and oxytocin. Foals were categorized into 4 groups according to their ability to adapt in, and survive, the neonatal period. Group A had no demonstrable coordinating reflexes, were weak from birth, and all died within 90 minutes. Group B had some righting reflexes, but had poor coordination and a weak suck reflex. They showed some improvement for about 2 hours, but all died within 9 hours. Group C foals had a good suck refl...
Two cases of abnormal equine pregnancy associated with excess foetal fluid. THE accumulation of a gross excess of fluid in the amniotic or
allantoic cavities is not uncommon in bovidae, although the
latter occurs most frequently. The resulting pathological
conditions are usually referred to as hydrops amnii and
hydroallantois, respectively. They are often associated with
abnormalities of the foetus in cattle (Vandeplassche el ul1965;
Roberts 1971) and hydro-allantois is quite common in twin
pregnancies (Roberts 1971).
This article describes two cases of excess foetal fluid in the
mare, both of which were associated with abnormal
pregnancies.
Interrelationships between uterus and conceptus to maintain corpus luteum function in early pregnancy: sheep, cattle, pigs and horses. Processes associated with "Maternal Recognition of Pregnancy" are reviewed extensively from the ovine, bovine, porcine and equine species. Comparisons among these species indicate that CL maintenance is achieved primarily by a predominant antiluteolytic-anti PGF effect, and there is strong evidence for antiluteolytic-luteoprotective and luteotropic controls that complement this basic system. The nature of the chemical signals (steroids, prostaglandins and proteins) to regulate these processes among the species are described. Common to all of the species reviewed is a change in vascular dynamic...
Attempted conversion of twin to singleton pregnancy in two mares with associated changes in plasma oestrone sulphate concentrations. The removal of one of twin embryos was attempted by infusion of 24% (w/v) saline into the gestation sac in 2 mares by laparotomy. The treatment was successful in one mare (Case 1) and the untreated embryo remained viable. However, neither foetus survived in the second mare (Case 2). Plasma oestrone sulphate (E1S) concentrations fell immediately after treatment in both mares but recovered to approximately 50% of pretreatment levels in Case 1. In Case 2 plasma E1S concentrations declined steadily and were less than 1 ng/ml within 6 days of treatment. These preliminary results suggest that the me...
Fetal and maternal heart rates in a case of twin pregnancy of the Thoroughbred horse. Fetal electrocardiogram in a twin pregnancy of a Thoroughbred horse was recorded. Two colts were born alive at 340 days of gestation. One was healthy but the other was growth-retarded. Both fetal heart rates decreased similarly with gestational age, but the discrepancy was noted from 4 days before parturition. The higher heart rate seemed to be obtained from the growth-retarded colt. Maternal heart rate increased gradually with the advancement of gestational period and then increased prominently during the last 2 weeks before parturition.
A new procedure for the cryopreservation of equine embryos. Early equine blastocysts and blastocysts were collected nonsurgically at six days post-ovulation. Thirty-two embryos were randomly assigned to a 2x2 factorial design. Factors were: 1) 0.5-ml straws or 1-ml glass ampules; and 2) plunging into liquid nitrogen (IN(2)) at -33 C or -38 C. Cryoprotectant, 10% glycerol in PBS plus 5% fetal calf serum (FCS) was added in two steps, 5% then 10%. Embryos were cooled at 4 C/min to -6 C and then seeded, 0.3 C/min to -30 or -35 C and 0.1 C/min to -33 or -38 C. Samples were thawed in 37 C water and glycerol removed in six steps, 10 min per step. Embryo quali...
Embryonic loss in mares: Incidence and ultrasonic morphology. Pregnancy was determined by ultrasound on Days 11, 15, 20, 25, 30, 35, 40, 45, and 50 in 154 ponies and 27 horses. In ponies, the embryonic loss rate for Days 11 to 15 (28 154 , 18.2%) was greater (P<0.01) than for any of the subsequent five-day intervals (0% to 3.3%). There were no losses during Days 11 to 15 in horses (0 27 ), and the difference between ponies and horses was significant. The loss rates for the seven periods encompassing Days 15 to 50 were not significantly different among periods. Pseudopregnancy occurred more frequently (P<0.01) following embryonic loss after Day 20 (...
[Progesterone in mare’s milk: suitable for early pregnancy detection?]. The concentrations of progesterone in milk were determined in twenty-one mares to establish a diagnosis of pregnancy in an early stage (15-19 days). Progesterone levels varied from 0.0 to 4.2 ng/ml in nine non-pregnant mares and from 6.7 to 30.0 ng/ml in twelve pregnant mares. Progesterone levels were determined by an enzyme-linked immunosorbent assay (ELISA).
Fertility of young mares after long-term anabolic steroid treatment. The effect of prior treatment with anabolic steroids was studied in 46 three-year-old mares. In the preceding year, these mares had been assigned to 1 of 4 treatment groups and had received the manufacturer's recommended dosage of 1.1 mg of boldenone undecylenate (BU)/kg of body weight, 4.4 mg of boldenone undecylenate (4 BU)/kg, 1.1 mg of nandrolone decanoate (ND)/kg, or 0.04 ml of sesame oil/kg (control, C). Mares had received an injection every 3 weeks for 54 weeks for a total of 19 injections, with the final injection in December. In the following breeding season, fewer (P less than 0.05) ...
Effect of age of equine embryos and method of transfer on pregnancy rate. A 2 X 2 cross-classified experiment was conducted to investigate the effect of age of equine embryo (7 vs 8 d postovulation) and method of transfer (surgical vs nonsurgical) on pregnancy rates at 50 d of gestation. Embryos were recovered 7 or 8 d postovulation using a Foley catheter and 3 liters of modified Dulbecco's phosphate-buffered saline (PBS). Upon identification, the embryos were placed in millipore-filtered PBS containing 20% heat-inactivated steer serum and maintained at room temperature until transferred. At the time of recovery, embryos were randomly assigned to be transferred eith...
Serial investigations of early pregnancy in pony mares using real time ultrasound scanning. The uteri of 13 pony mares were examined daily by ultrasound during the first two months of gestation. The conceptus was first identified between 12 and 16 days after ovulation and the embryo was seen on the ventral surface of the conceptus after Day 21. The foetal heart could be visualised after Day 22 and spontaneous movement of the foetus occurred after Day 39. No consistent pattern was seen in the development of the foetal membranes, although attachment of the umbilical cord to the allantochorion was always on the dorsal aspect of the conceptus. Daily measurements were made of the diameter...
Techniques and applications of transabdominal ultrasonography in the pregnant mare. To establish the feasibility of utilizing high-frequency ultrasound to image equine fetal development transabdominally, in vitro and in vivo observations were made. Three fetuses retrieved from mares that died from various causes were scanned in vitro to establish fetal images from various orientations. A total of 50 mares ranging in age from 4 to 16 years and representing various breeds were scanned intermittently from 100 days of gestation to parturition. Fetal parts, amniotic fluid, placental membranes, and motion patterns could be reliably identified. Fetal heart rates decreased from 180 b...
Characterization of intrauterine mobility of the early equine conceptus. Intrauterine mobility patterns of the embryonic vesicle were characterized on Days 9 to 17 after ovulation in pony mares using real-time ultrasonography (n=5 or 7 mares per day). The location of the vesicle was determined by dividing the uterus into right horn, left horn, and body. Each uterine horn was further divided into three approximately equal portions (cranial third, middle third, caudal third), yielding seven segments (body plus three portions of each horn). Location of the vesicle within the uterus was recorded every five minutes for two consecutive hours (25 location determinations p...
Lymphocyte alloantigens of the horse. II. Antibodies to ELA antigens produced during equine pregnancy. Evidence is presented for a reproducible maternal immune response to histocompatibility antigens during equine pregnancy. Mares were stimulated as a result of pregnancy to produce cytotoxic antibodies to paternal lymphocyte alloantigens. The majority of these antibodies were directed against antigens of the equine lymphocyte antigen (ELA) system, which is the major histocompatibility complex (MHC) of the horse. In 16 experimental pregnancies produced using 12 mares and 4 stallions which had been typed for ELA antigens, there was correlation between ELA incompatibility between sire and dam and ...