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Topic:Hormones
Hormones in horses are chemical messengers produced by various glands and tissues, regulating numerous physiological processes essential for maintaining homeostasis. These hormones influence a wide range of functions, including growth, metabolism, reproduction, and stress responses. Key hormones in equine physiology include cortisol, estrogen, testosterone, and insulin, among others. The levels and effects of these hormones can vary based on factors such as age, sex, and environmental conditions, impacting overall health and performance. This page compiles peer-reviewed research studies and scholarly articles that explore the production, regulation, and physiological roles of hormones in equine biology.
Oestrus and pregnancy diagnosis by milk progesterone assay in the mare. The milk progesterone profiles of four mares were followed daily for four to five weeks after foaling. Progesterone was determined by direct radioimmunoassay using iodinated progesterone as the labelled antigen. The milk progesterone concentration varied from 1 to 5 nmol/1 (0·3 to 1·6 μg/1) during the first 10 days after foaling. The first ovulation took place at about the tenth day. During the luteal phase milk progesterone levels rose dramatically, reaching a maximum level of 30 to 45 nmol/1 (9·4 to 14·2 μg/1) within five to 10 days, and then fell to low levels unless pregnancy followe...
Plasma progesterone levels in the mare during the oestrous cycle and pregnancy. Plasma progesterone was determined with the aid of a competitive protein-binding assay in mares during the oestrous cycle, early pregnancy (45--60 days) and later pregnancy (2--10 months). Progesterone levels were low during oestrus (less than 1 ng per ml) (3,18 nmol/l) and reached high levels (often in excess of 10 ng per ml) (31.8 nmol/l) within 3--4 days after ovulation. The high luteal levels were maintained for approximately 5--8 days and then declined sharply over a period of approximately 24--48 hours to reach low levels at the subsequent oestrus period. In mares conceiving after servic...
beta-Endorphin: isolation, amino acid sequence and synthesis of the hormone from horse pituitary glands. Beta-endorphin has been isolated from equine pituitaries. Its amino acid sequence is identical to that of ovine, bovine and camel beta-endorphins except for substitution of the threonine residue at position 6 by serine. The equine beta-endorphin has also been synthesized by the solid-phase method. In comparison with the human hormone, equine beta-endorphin was shown to possess 3 times the receptor-binding activity in rat membrane preparations and 1.6 times the analgesic potency in the mouse tail-flick assay.
Behavioral, follicular and gonadotropin changes during the estrous cycle in donkeys. Sexual behavior, follicular development and ovulation, and concentrations of circulating gonadotropins during the estrous cycle were studied during the summer in 7 jennies. Mean behavioral estrous length was 6.4 +/- 0.6 days (mean +/- SEM, n=19; 5.6 +/- 0.5 days preovulatory and 0.8 +/- 0.2 days post-ovulatory). Mean diestrous length was 19.3 +/- 0.6 days (n=14). Females in estrus typically showed posturing, mouth clapping, clitoral winking, urinating and tail raising. Mouth clapping began approximately one day sooner and lasted approximately one day longer than winking and tail raising, so th...
Biological functions and receptor binding activities of equine chorionic gonadotrophins. The role of equine chorionic gonadotrophin (CG, formerly termed Pregnant Mare serum Gonadotrophin, PMSG) in maintaining equine pregnancy was investigated by examining the effects of this hormone on the maternal ovaries during early gestation and relating these findings to the receptor binding activities of CG in vitro. Measurement of plasma progestagen profiles in mares and donkeys carrying horse, donkey, mule ( female horse X male donkey) and hinny (female donkey X male horse) conceptuses confirmed that CG induced several secondary ovulations and thus maintained maternal progestagen concentra...
Hormonal changes associated with long distance exercise. The alteration in plasma concentration of a number of hormones was investigated following an 80 km endurance ride. A marked rise in plasma cortisol levels occurred in all 17 animals investigated. Although decreased glucose levels did not occur in all animals, insulin levels fell in all horses examined. A high correlation (r = 0.89) was found between post ride glucose and plasma insulin concentrations. The plasma levels of both noradrenaline and adrenaline were significantly elevated post ride.
Puberty in the female pony: reproductive behavior, ovulation, and plasma gonadotropin concentrations. Reproductive behavior and gonadotropin concentrations were studied in 14 female ponies during the period from 10 to 21 months of age (February 1978 to January 1979). Nine fillies were born during April of 1977 (spring-born) and five were born during the summer and fall of 1977 (late-born). Three of the spring-born fillies had been ovariectomized (OVX) at 4 months of age. All intact spring-born fillies ovulated during late spring when they were 12–15 months old. Two of five late-born fillies did not ovulate, and there tended to be fewer ovulations and a shorter breeding season in late-born th...
Effect of manipulating central catecholamines on puberty and the surge of luteinizing hormone and gonadotropin releasing hormone induced by pregnant mare serum gonadotropin in female rats. We have investigated the effect of manipulating central catecholamines on the timing of puberty (as assessed by vaginal opening) in female rats and the surge of luteinizing hormone (LH) and gonadotropin releasing hormone (GnRH) induced by pregnant mare serum gonadotropin (PMSG) in immature female rats. Manipulation of the catecholamines was carried out with either 6-hydroxydopamine (6-OHDA) administered with or without either desipramine (DMI) or pargyline, or alpha-methyl-p-tyrosine (alpha-MPT). The neonatal administration of 6-OHDA delayed puberty, an effect which was potentiated by pretreat...
[Study, after stopping treatment, of the consequences of the injection of male hormones in mares on their social behavior and hierarchical position]. The androgenization of a more belonging to a social group where it held a stable hierarchic rank, or a mare recently admitted to this group, increases their status in the hierarchic order and the position acquired is subsequently maintained; in some cases, they continue to rise in the hierarchic order long after the injections of male hormones has been stopped. Some elements of the social behaviour of a stallion appear during the treatment; these elements may persist long after the mares have regained their female hormone balance, corroborated by the establishment of a standard pregnancy.
GnRH localization in the equine brain and infundibulum: an immunohistochemical study. Immunohistochemical localization of the decapeptide gonadotropin releasing hormone (GnRH) in neural structures in the pony brain and infundibulum (INF) was conducted at the light-microscopic level. This procedure utilized an antiserum generated against GnRH conjugated to bovine serum albumin. In the rostral INF, GnRH was distributed mainly in the external layer, with greatest concentrations adjacent to the long capillary loops of the hypophyseal portal system. The intermediate portion of the INF contained the hormone throughout the external layer, especially in the dorsolateral regions just ve...
Vaginal pH during estrus in mares. Vaginal hydrogen ion concentration of Saddlebred mares was measured throughout the behavioral estrous period. The mean pH on the day of ovulation was significantly (P = <.01) lower than on all other tested days of estrus. Follicular development and vaginal pH values in pony mares at time of slaughter were highly correlated. A significant decrease in vaginal pH values, determined through a series of carefully monitored measurements during estrus, was found to be characteristic and indicative of ovulation.
Physico-chemical properties of pregnant mare serum gonadotropin. Pregnant mare serum gonadotropin exhibits a dissociation at acid pH as shown by the drop of s20,w values from 3.52 S at pH 8.1 to 2.52 S at pH 2.0. The dissociation is accompanied by an absorbance change with a maximum at 287 nm and a parallel loss of both follicle-stimulating hormone (FSH) and luteinizing hormone (LH) activities as followed by radioreceptor assays. The apparent pKa of the acid transition is 3.45 with an extremely slow and temperature-dependent rate at pH 2.0 (1.8 . 10(-4) s-1 at 37 degrees C). By gel filtration the molecular weight of the active hormone is estimated to be 45 ...
A complication of cryptorchid castration in three horses. During an 8-month period, 3 horses were examined because of incomplete cryptorchid castration. Each horse had had surgery to remove 1 retained testis. In each case, the attending veterinarian believed castration had been adequately completed. History, rectal examination findings, and in 2 cases, high serum testosterone concentration were factors that led to the decision to do exploratory surgery on each horse. In each case, initial surgery had resulted in surgical removal of the tail of the epididymis, which was mistaken for testicular tissue.
Variations in the properties of equine chorionic gonadotropin. The objectives of this paper are to review the chemical and biological properties of equine chorionic gonadotropin (eCG, PMSG) isolated from the serum. Comparisons are made with eCG isolated from endometrial cups, trophoblast cell culture medium, and low titer serum. The results show that eCG can vary, depending on the source, in both chemical and biological (LH and FSH activity) properties.
Influence of season and age on reproductive activity in pony mares on the basis of a slaughterhouse survey. Reproductive tracts were collected monthly over a 3-year period from 1,003 nonpregnant ponies at a slaughtering plant in Wisconsin. Ages of the animals were estimated from tooth replacement and wear. Ovaries were examined for follicular and luteal activity. There were no differences between left and right ovaries in size or occurrence of ovulation. The frequency of multiple ovulations, 10%, was higher than previously reported for ponies. The follicular changes during the ovulatory cycle did not support a two-wave theory of follicular growth. Ovarian activity changed seasonally, a finding simil...
A biochemical study of the Arab Horse Society’s marathon race. Blood samples were taken before and after a cross country race over the marathon distance of 42 km. There was a rise in blood glucose and plasma free fatty acids and glycerol associated with a rise in plasma cortisol and glucagon but the fall in insulin was not significant (P > 0.05). Plasma potassium and albumin concentrations increased, calcium decreased and there was no change in sodium or bicarbonate concentrations. There was an increase in plasma urea, creatinine, uric acid, bilirubin and isocitrate dehydrogenase but no change in alkaline phosphatase. There was a rise in plasma creatin...
Sexual behavior, seminal pH and accessory sex gland weights in geldings administered testosterone and(or) estradiol-17 beta. Sixteen stallions were castrated and 30 days later assigned to one of four treatments: (1) testosterone propionate (175 microgram/kg body weight), (2) 17 beta-estradiol-3-benzoate (44 micrograms/kg body weight), (3) a combination of both steroids or, (4) vehicle only. These dosage were administered every other day for 18 days. The dosages were then doubled and continued for 20 days. Concentrations of testosterone and estradiol in serum decreased rapidly after castration and stabilized within about 6 hours. Mean concentrations of testosterone and estradiol maintained by the steroids were 1.4 an...
