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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.
Fixation and orientation of the early equine conceptus. Fixation and orientation of the conceptus within the uterine lumen of 40 barren mares were examined by ultrasound daily on days 11-21 and at three-day intervals thereafter until day 48. The growth curve of the in situ conceptus had a distinct plateau between days 17-24, as determined by measurements of the width and area of conceptuses on the ultrasound images. The vesicle expanded at an average daily rate of 3-4 mm before the plateau and 2-3 mm after the plateau. Dramatic changes occurred in the shape of conceptus. The predominant shapes were approximately as follows: days 11-16, spherical; d...
Methods for the treatment of twin pregnancy in the mare. Within a group of 130 mares which, in the event, carried twin pregnancies, 29 (22.3 per cent) produced their twins following diagnosis of a single palpable follicle at service and a single pregnancy 42 days later. The whole group of 130 twin-pregnant mares gave birth to only 17 live foals (13 per cent). Breeding results for the following season were available for 102 of these mares, when 38 (37 per cent) produced live foals. Thus over the two seasons an average 23 per cent of this group produced live foals. In a second group, comprising 70 mares, twin pregnancy had been diagnosed in all of the...
Comparison of glucose, fructose, ascorbic acid and glucosephosphate isomerase enzymatic activity in uterine flushings from nonpregnant and pregnant gilts and pony mares. In Experiment 1, 40 gilts and 30 pony mares were used to characterize changes in glucose, fructose, ascorbic acid and glucosephosphate isomerase (GPI) enzymatic activity in uterine flushings collected either during the estrous cycle or early pregnancy. Total recoverable glucose was greater (P less than 0.01) in uterine flushings from pregnant gilts, but pregnancy status had no effect on total recoverable glucose in pony mare uterine flushings. Fructose was undetectable in uterine flushings from nonpregnant gilts and pony mares and pregnant gilts and pony mares prior to Day 14, but occurred in ...
Foetal monstrosity in a thoroughbred mare resembling schistosomus reflexus. This study discusses a case of foetal abnormality resembling schistosomus reflexus in a thoroughbred mare, noting its similarity to documented instances in bovines and pointing towards the need for more [...]
Influence of photoperiod on the pregnant and postpartum mare. Over a 2-year period, mares (n = 32) of predominantly Quarter Horse breeding and their foals were used to study the effects of photoperiod on reproduction during the periparturient period. Specific objectives of the study were (i) to evaluate the effects of an extended photoperiod regimen (16 hours' light) on gestation length, foal development, and postpartum reproductive performance, and (ii) to measure changes in plasma progesterone concentrations during the last trimester of gestation and plasma luteinizing hormone (LH) concentrations after foaling until ovulation. Mares in the extended day...
Induction of parturition in the mare with prostaglandin F2 alpha. Thirty-one mares of Quarter Horse and Thoroughbred breeding were utilized in two experiments to evaluate the efficacy of prostaglandin F2 alpha (PGF2 alpha) for induction of equine parturition and to monitor the effects of this treatment on viability of the resulting foals. Three of five mares given 5 mg PGF2 alpha (im) on day 338 of gestation foaled 19.6+/-8.2 hr postinjection. In the second experiment immediately following 3 daily injections of 10 mg estradiol cypionate (ECP) given on days 326, 327 and 328 of gestation, seven mares were infused (iv) with PGF2 alpha at the rate of 1.3 mg/hr f...
Breeding behaviour of a stallion at pasture with 20 mares in synchronized oestrus. A 6-year-old stallion was placed in a pasture for 9 days with 20 mares in which oestrus was synchronized with two treatments of PGF-2 alpha given 15 days apart. Breeding and observation began 3 days after the second treatment. Observations were carried out during the daylight hours (05:00 to 21:30 h). Eighteen mares showed oestrus and mated an average of 4.56 times each (range 1-12). There were 1.74 mounts per mating. The maximum number of matings by the stallion during 1 day was 16 on Day 2. The overall mean interval between matings was 72.8 min, ranging from 34.5 min on Day 1 to 128.7 on Day...
A comparison of agents for inducing parturition in mares in the pre-viable and premature periods of gestation. Various regimens of prostaglandins, alone or followed by oxytocin, were given to induce parturition in mares during the pre-viable and premature periods of gestation and in near-term mares. The most successful method of induction was found to be 2 i.m. injections of 500 micrograms fluprostenol (Equimate: I.C.I.) at a 2-h interval followed (if necessary) by 10-20 i.u. oxytocin injected i.v. in 5 i.u. serial increments every 15-20 min. Peak concentrations of the prostaglandin metabolite (PGFM) in response to the inducing agents were shown to be associated with delivery at, but not before, 320 da...
Blood gas and acid–base status in spontaneously delivered, term-induced and induced premature foals. Six spontaneously delivered foals, 8 Thoroughbred foals induced at term with fluprostenol and 17 Pony foals induced prematurely with fluprostenol and oxytocin at a gestational age of 270 to 330 days were studied to determine PO2, PCO2, pH, base excess and HCO3 values in arterial blood between birth and 7 days of age. The Pony foals were subdivided into those that survived greater than 24 h (N = 9) and less than 9 h (N = 8). Blood gas and acid base values in the term-induced foals were similar to those in spontaneously delivered foals. The induced premature foals surviving greater than 24 h had...
Ultrasonic echography in the mare. Ultrasonic echography in the mare allows pregnancy diagnosis as early as Day 14 after ovulation. In the 1980 and 1981 breeding seasons, a total of 7438 examinations of 4688 mares were performed on several farms with the same apparatus. The accuracy of positive pregnancy diagnosis was estimated to be greater than 95% and of non-pregnancy diagnosis greater than 84%. When abnormal pictures of vesicles are found, it has to be decided whether it is a conceptus or a cystic structure. Most small vesicles do not develop, whereas large ones, deformed shapes, presence of some echoes, or a division insid...
Progesterone, prostaglandin F-2 alpha, PMSG and oestrone sulphate during early pregnancy in the mare. Blood samples from 4 mares during the late luteal phase, oestrus, early pregnancy and up to about 150 days of gestation were analysed for 15-keto-13,14-dihydroprostaglandin F-2 alpha (PGFM), progesterone, PMSG and oestrone sulphate by radioimmunoassays. During the late luteal phase, at the time of corpus luteum regression and decreasing progesterone levels, PGFM peaks were recorded. During early pregnancy (i.e. from mating and up to about Day 30) no such peaks were detected. After mating the progesterone levels increased and remained high throughout the observation period. During the oestrous ...
Chemical composition of the spinal cord in the normal developing fetus and in the premature foal. The lipid content of spinal cord, expressed as a percentage of adult values, was considerably higher for newborn foals than for several other species and traces of esterified cholesterol (type A) were only rarely present in horse fetal cord (from 270 days gestational age onwards). This suggested that, at birth, the spinal cord is neurochemically more 'mature' in the horse than in cattle, sheep and pigs. Data for premature foals revealed no lipid abnormality suggestive of myelin immaturity or degeneration.
Termination of twin gestation by blastocyst crush in the broodmare. Manual crushing of one blastocyst performed on 181 bicornuate twin pregnancies between Days 24 and 45 has shown that the uncrushed blastocyst can either survive and develop normally to full term or may be rejected and resorbed like its crushed twin, depending mainly on the stage of pregnancy. Crushing, which causes rupture of fetal membranes, results in a rapid fall in the survival rate of the uncrushed blastocyst when performed after Day 31. In some mares rupture is not possible after Day 35 even if extreme pressure is used. Crushed, but unruptured, blastocysts mainly between Days 35 and 45 m...
Ultrastructural study of the development of the pars distalis (anterior pituitary) in the foal. The pituitary glands of 4 horse embryos (41-55 days of gestation) were examined by light microscopy, and the pars distalis from 10 fetal foals (75-300 days) was examined by electron microscopy. At Day 41 the development of Rathke's pouch and the saccus infundibuli was advanced; the former had almost lost its connection with the stomodaeum and the latter had started to differentiate into infundibular process and infundibular stalk. By Day 43 Rathke's pouch was completely dissociated from the stomodaeum and its walls were beginning to show uneven growth. The ventral wall of the pouch, the future...
Some aspects of tissue maturation in fetal and perinatal foals. Collagen, elastin and structural glycoprotein content of the lungs of 38 fetal and neonatal foals, 8 of which were showing dysmaturity or convulsive syndrome, were measured by standard biochemical means. Glycoprotein content showed little or no change between 100 and 340 days of gestation; elastin remained constant from 100 to about 260 days when there was an exponential increase up to the time of birth, while collagen content rose linearly from 100 days to birth. In dysmature animals there was significantly less collagen in the lungs at birth but the difference in elastin content between the ...
Concentrations of progesterone, 17 alpha-hydroxyprogesterone and 20 alpha-dihydroprogesterone in the plasma of mares during pregnancy and at parturition. Plasma concentrations of progesterone and 17 alpha-hydroxyprogesterone were high in the 2nd and 3rd months of gestation, but 20 alpha-dihydroprogesterone increased from a level of 2 ng/ml, during the first 3 months, to 10-15 ng/ml during months 5-10, to reach 80-120 ng/ml during the last 30 days before foaling.
Surgical management of uterine torsion in the mare: a review of 26 cases. Uterine torsion was diagnosed in 26 mares of various breeds. The mean duration of gestation was 9.6 months. The most common clinical history was intermittent unresponsive colic of varying duration. Diagnosis of uterine torsion was confirmed by rectal palpation, and surgical correction was achieved in most cases by standing flank laparotomy and manual repositioning of the gravid uterus. Recumbent laparotomy was used only if the mare was intractable, the uterus was ruptured, or hysterotomy was indicated. Of 20 foals determined to be alive during surgery, 14 (70%) were subsequently born alive.
[Evaluation of variability of duration of pregnancy in mares]. In a set of mares of English Thoroughbred horse of the Napajedla stock the gravidity length in the time period from 1880 to 1972 was evaluated. The variability of the gravidity length was evaluated in sets which were put together by combination of two age groups with a division of the studied time period into ten-year stages. Variance and sample means of the gravidity lengths in these sub-groups are significantly different in the period under study. In order to eliminate the action of non-genetic influences qualifying the variability of the gravidity length, and to increase the objectivity of ...
The use of endometrial biopsy in the infertile mare. The results of a study on endometrial biopsies obtained from 700 infertile mares are reported. Infiltrative endometritis was present in 51% consisting of a combination of an acute and chronic cellular response in 6%, mild chronic infiltrations in 35% and moderate to severe chronic infiltrations in 10%. Demonstrable endometrial fibrosis was found in 88% of the mares with the majority having mild (51%) or moderate (35%) changes. The age of the mares and the average number of years barren gradually increased with the severity of endometrial fibrosis, as did the combined incidence of fetal loss (e...
Development of the adrenal cortex in the fetal foal: an ultrastructural study. The adrenal cortex from twelve fetal foals (gestational ages from 61 to 300 days) was examined by light and electron microscopy. Adrenal glands from three newborn foals were also examined by light microscopy. Between 61 and 100 days of gestation the adrenal cortex became organised into two distinct regions, the zona glomerulosa and zona fasciculata, which grew steadily in thickness until the 300th day. Between 300 days and birth there was a dramatic increase in the width of the zona fasciculata. From 200 days a narrow band of compact cells marked the cortico-medullary border. Though these cell...
Relationship between early pregnancy site in consecutive gestations in mares. The records of 200 pairs of consecutive pregnancies in mares showed that in 82 per cent of cases the second pregnancy was initially established in the opposite uterine horn to that of the first, irrespective of the parturition to conception interval. This relationship also occurred when the first pregnancy ended in abortion after 140 days but not if it terminated before this time.
Coat color and gestation length in thoroughbred mares. Average gestation periods for bay, chestnut, dark bay, gray, and black Thoroughbred mares were compared. A total of 1359 gestation periods were used. A linear model including factors for age of mare, sex of foal, month and year of breeding, and sire effects was used in the analysis. Dam and sire coat-color combinations were also investigated in a similar manner. No significant differences in gestation length could be attributed to coat color of the mare of to dam and sire coat-color combinations. Heritability of gestation length was estimated to be 0.38. The results of this study strongly sugg...
