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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.
Secretion of free and conjugated steroids by the horse testis into lymph and venous blood. In 3 testes of 2 adult Pony stallions under halothane anaesthesia, catheters were inserted into a vein and a lymphatic vessel in the spermatic cord and into a vein on the surface of the testis. Lymph and venous blood were collected from the catheters in the cord and p-aminohippurate (2% w/v, 0 . 1 ml/min) was infused into the vein on the testis to determine blood flow by dilution. After 1 h, 6000 i.u. hCG was injected i.v. and collections continued for 45 min. The testes weighed 126-176 g. Lymph flow was 20-150 microliter/min before hCG and 100-270 microliter/min after hCG; the range of blood ...
Control of ovulation in mares in the early breeding season with ovarian steroids and prostaglandin. Two trials were conducted to (1) determine the degree of control of ovulation achieved by treating mares in late winter with progesterone and oestradiol-17 beta combined after prior exposure to an artificially increased photoperiod, and (2) to examine the effectiveness of such a procedure incorporated into equine breeding farm management systems. Following a 15-day treatment of 150 mg progesterone and 10 mg oestradiol-17 beta daily with 10 mg PGF-2 alpha on the last day of steroid treatment, 27 of 31 mares ovulated on Days 8-14 after the last injection in one trial. Conception rate for mares m...
Seasonal and individual effects on ovarian and endocrine responses of mares to a synchronization treatment with progestagen-impregnated vaginal sponges. The 8 saddle-type mares were treated with progestagen-impregnated vaginal sponges for 8 days and prostaglandin on the day of sponge removal. The treatment was given at random days of the cycle in April, May, July and September. Sponge insertion induced a sharp decrease in LH levels; at sponge removal, there was an immediate increase in LH and a large FSH rebound. Ovulation was synchronized 11 +/- 2 . 8 days (s.d.) after the end of treatment. In April the interval from sponge removal to ovulation was longer (14 days compared with 10 . 1, 10 . 7 and 10 . 2 days), the basal and peak LH levels low...
Species specificity of estrogen biosynthesis in pregnancy. Immunochemical difference of placental NADPH-cytochrome c (P-450) reductase in human, baboon and horse. NADPH-cytochrome c (P-450) reductases from human placental aromatase II and from horse placental microsomes were solubilized and purified to show a single band of 83,000 daltons in SDS-polyacrylamide gel electrophoresis. Rabbits were immunized with purified human placental aromatase II NADPHcytochrome c (P-450) reductase. The resulting antibodies (Reduc-Ab) were used to examine the species specificity of estrogen biosynthesis and the reductase activity in humans, baboons, horses and rats. Rcduc-Ab suppressed androstenedione aromatase activity in human, baboon and horse placental microsomes wit...
Influence of prostaglandin F2 alpha on sperm production and seminal characteristics of the stallion. Six mature stallions were used to test the effect of prostaglandin F2 alpha (PGF2 alpha ) on sperm production and seminal characteristics. Semen was collected from each stallion twice weekly 1 hr following a 10 mg intramuscular injection of PGF2 alpha or a sham injection. A switchback design was used so that three stallions received PGF2 alpha and three served as controls during the first 9 weeks (period 1). Treatment regimens were reversed during the second 9 weeks (period 2). Treatment of stallions with PGF2 alpha resulted in an increase (P less than .05) in gel free seminal volume and a dec...
Plasma oxytocin concentrations in cyclic mares and sexually aroused stallions. An experiment was conducted to measure plasma oxytocin concentrations at 4 different stages of the estrous cycle in 11 pony mares. Plasma oxytocin concentrations (muU/ml +/- SE) were found to be higher (P<.01) on day 2 of estrous (39.8 +/- 12.5) and day 5 post-ovulation (33.1 +/- 12.0) than on day 10 (2.3 +/- 1.6) and day 15 post-ovulation (6.8 +/- 4.1). A second experiment was conducted to measure jugular plasma oxytocin concentrations before and after sexual arousal in six pony stallions. Oxytocin concentrations (muU/ml +/- SE) were higher (P<0.06) after sexual arousal (50.5 +/- 8.9) than be...
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.
Restoration of reproductive capacity of stallions after suppression with exogenous testosterone. Twelve stallions that had been given 0, 50 or 200 micrograms testosterone propionate (TP)/kg body weight every other day for 88 days were examined for the effects of androgen withdrawal on spermatozoal production, seminal quality and libido. Although the lower dosage did not affect most of the traits studied, the higher dosage severely reduced scrotal width, spermatozoal production, the number of sperm per ejaculate, the percentage of progressively motile spermatozoa and the percentage of normal spermatozoa. These adverse effects were found to be largely reversible. By 90 days after the cessat...
Clinical, morphological and endocrinological aspects of cryptorchidism in the horse. The authors analysed clinical, histological and hormonal data obtained from 205 cryptorchid horses. The majority of the unilaterally and bilaterally retained testes were located in the inguinal canal; however, the ratio of inguinal vs abdominal retention appeared to decrease with advancing age. In unilateral cryptorchidism, a pronounced preference was noted for left abdominal retention, whereas for inguinal cryptorchids, the retained testes occurred equally on both sides. Right inguinal retention was found to decrease with advancing age. Histology of cryptorchid testes revealed apparently norm...
Equine follicle-stimulating hormone. Purification, acid dissociation, and binding to equine testicular tissue. A simple method of purification of equine follicle-stimulating hormone is described by which two forms of the hormone are obtained. The acid dissociation of the most active preparation was studied and a pKa of 5.8 was determined at 37 degrees C. This value is 2 pH units higher than that observed for pregnant mare serum gonadotropin suggesting that the binding areas between subunits are not identical in the two hormones. We also describe an homologous radioreceptor assay of equine follicle-stimulating hormone which is highly specific for this hormone in contrast to the heterologous systems desc...
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...
Immunochemical and biological properties of horse parathyroid hormone. No abstract available
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...
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.
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...
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...
