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.
Bailey MT, Christman SA, Wheaton JE, Troedsson MH, O'Brien TD, Ababneh MM, Santschi E.The aim of this study was to examine inhibin production in granulosa-theca cell tumours (GTCT). The experimental aims were: (i) to determine GTCT cell types that produce inhibin alpha- and betaA-subunits; (ii) to determine whether alpha- and betaA-subunit forms differ in GTCT fluid and normal equine follicular fluid (eFF); and (iii) to determine whether dimeric inhibin (alpha betaA) is present in GTCT plasma and tumour fluid. Plasma, tumour fluid and tumour tissue were collected from mares (n=6) with GTCT. Plasma and eFF were collected during the follicular phase from mares (n=4) undergoing no...
Greaves HE, Porter MB, Sharp DC.Long-term ovariectomized Pony mares were treated with oestradiol (0.2-5.0 mg; i.m.) at 12 h intervals for 10 days. Blood samples were collected by jugular venepuncture three times a day throughout the experiment and additional blood samples were collected at 15 min intervals for 12 h on days 0 and 10 (sampling periods 1 and 2, respectively). There were significant effects of oestradiol treatment (P < 0.05) and oestradiol treatment x day (P < 0.0001) on the mean LH concentrations each day. Regression analysis of LH time trends each day indicates that there is heterogeneity (P < 0.001) ...
Gerstenberg C, Allen WR.Branched tubular endometrial glands are key features of the uterine lining in mares. The epithelium in the neck regions of the glands is similar to that lining the lumen of the uterus, whereas the epithelium in the deeper, coiled portions of the glands secretes protein rich histotrophe or 'uterine milk' during dioestrus and pregnancy. The present study was performed to characterize endometrial histology in perinatal and peripubertal fillies and to investigate the influences of specific steroid treatments on endometrial gland development in the prepubertal period. Uteri obtained from equine fet...
Alexander SL, Irvine CH, Shand N, Turner J.Removal of opioid inhibition of GnRH neurones is thought to be a critical event in generating the ovulatory surge in some species. In the present study, a nonsurgical technique was used to collect pituitary venous blood samples from eight mares every 0.5-1.0 min for 1 h before and after administration of the opioid receptor antagonist naloxone (0.2 mg kg(-1), i.v.), to investigate whether opioid inhibition is also important in mares. Jugular blood samples were taken at 10-15 min intervals. Mares were studied 0, 1 or 2 days before ovulation. Naloxone administration increased mean rates of GnRH ...
Huszenicza G, Nagy P, Juhász J, Kóródi P, Kulcsár M, Reiczigel J, Guillaume D, Rudas P, Solti L.The relationship between thyroid function and seasonal reproductive activity in mares was investigated by comparing plasma triiodothyronine and thyroxine concentrations in anoestrous mares and in mares with cyclic ovarian activity during the anovulatory season. In study 1, the diurnal changes in plasma triiodothyronine and thyroxine concentrations on a single day were compared in anoestrous and cyclic mares. The mean thyroxine concentrations were significantly higher (P < 0.001) in the cyclic mares than in the anoestrous mares, whereas mean triiodothyronine concentrations were similar in bo...
Bergfelt DR, Adams GP.Two experiments were performed to determine the efficacy of ultrasound-guided transvaginal follicle ablation for synchronizing ovarian function in mares. The experiments were initiated at random stages of the oestrous cycle in control (nonablated) and follicle-ablated mares. On day 0, all follicles > or =10 mm in diameter were punctured, aspirated and curettaged in ablated mares, and, on day 4, two doses of PGF2alpha were administered with a 12 h interval between the doses to both ablated and nonablated (control) mares. In Expt 1, hCG was administered to the ablated mares on the first or se...
Forhead AJ, Broughton Pipkin F, Taylor PM, Baker K, Balouzet V, Giussani DA, Fowden AL.Blood pressure, heart rate and the plasma concentrations of cortisol and components of the renin-angiotensin system were measured in chronically catheterized Pony mares (n=15) and their fetuses during the second half of gestation (day 153-336 of gestation; term is normally between day 320 and day 340 of gestation). Fetal blood pressure increased towards term with the prepartum surge in plasma cortisol concentration, and there was a correlation between fetal blood pressure and both gestational age (r = 0.88, P < 0.0005) and plasma cortisol concentration (r = 0.88, P < 0.0005). Plasma concentrat...
Card CE, Manning ST.Fetal maturation and equine parturition are not understood fully, although the adrenal and thyroid glands are thought to have regulatory roles. Thyroidectomized equine fetuses undergo prolonged gestation, and spontaneous diseases such as thyroid musculoskeletal disease and gestational fescue endophyte exposure are also associated with delayed parturition. Thyroid musculoskeletal disease is characterized by: histologically hyperplastic thyroid glands, chondro-osseous dysplasia and dysgenesis, angular limb deformity, low resting thyroxine and triiodothyronine concentrations, and lack of response...
Schoon HA, Wiegandt I, Schoon D, Aupperle H, Bartmann CP.Different types of endometrial maldifferentiation were investigated by histopathological (haematoxylin-eosin (HE), periodic acid Schiff-alcian blue and picro-sirius red staining) and immunohistological (oestrogen and progesterone receptors, Ki-67 antigen, intermediate filaments and laminin) analysis of endometrial biopsy specimens from mares (n=34), most of which had been barren for at least 1 year. Two major features were observed: (i) unequal differentiation, in which two functional stages are visible within a single biopsy sample: areas which are differentiated in accordance with the stage ...
Nikolakopoulos E, Kindahl H, Watson ED.Mares resistant (n=7) and susceptible (n=9) to persistent mating-induced endometritis were artificially inseminated (AI) during oestrus with chilled extended semen. Blood samples were collected from 30 min before AI, for 2 h after AI and again between 16 and 18 h after AI. Samples were assayed for oxytocin and the PGF2alpha metabolite 13,14-dihydro-15-keto PGF2alpha (PGFM). AI caused a significant increase in oxytocin concentrations in both the resistant and susceptible mares and there was no significant difference in oxytocin release between the two groups of mares. Mean PGFM concentrations w...
Behrendt-Adam CY, Adams MH, Simpson KS, McDowell KJ.In this study, the roles of oestrogen and progesterone in the regulation of oxytocin gene expression in equine endometrium were examined. Anoestrous mares (n=19) were assigned randomly to one of the following treatment groups: control (vehicle control for 1 day; n=3); progesterone (250 mg progesterone per day for 6 days; n=4); oestradiol (5 mg beta-oestradiol 17-valerate per day for 6 days; n=4); oestradiol plus short duration progesterone (5 mg beta-oestradiol 17-valerate per day for 6 days followed by 250 mg progesterone per day for 6 days; n=4); and oestradiol plus long duration progesteron...
Schmid RL, Kato H, Herickhoff LA, Schenk JL, McCue PM, Chung YG, Squires EL.In Expt 1, compact cumulus oocyte complexes (COCs) were matured in: (i) control medium (Hepes-buffered TCM-199 with 10% oestrous cow serum (OCS) + oestradiol, LH and FSH); (ii) Hepes-buffered TCM-199 with 20% follicular fluid; or (iii) control medium containing 250 ng progesterone ml(-1). Mature oocytes were collected by transvaginal aspiration as a positive control for the in vitro maturation (IVM) treatments. Oocytes were fertilized by ICSI and cultured in Menezo's B2 + 5% fetal calf serum (FCS). There were no significant differences among IVM treatments. In Expt 2, oocytes with expanded COC...
Stout TA, Lamming GE, Allen WR.In a recent study, continuous administration of oxytocin by subcutaneous minipump to mares from day 8 to 20 after ovulation prevented luteolysis in most of the treated but none of the control mares, indicating a role for oxytocin in cyclical luteolysis in mares. In the present study, measurement of oxytocin concentrations in uterine flushings recovered from nine mares during days 14-18 after ovulation gave values that were many times higher than those measured concurrently in peripheral plasma. Furthermore, intrauterine administration of oxytocin to four mares on day 14 after ovulation stimula...
Madill S, Troedsson MH, Alexander SL, Shand N, Santschi EM, Irvine CH.The aim of this study was to investigate the effect of different breeding stimuli on uterine contractility and pituitary oxytocin release in five oestrous mares, in order to design better treatments for mares with defective physical uterine clearance mechanisms. Electrodes and strain gauges were implanted surgically on the uterine myometrium and myometrial activity was monitored with a Grass polygraph. A catheter was placed non-surgically in the intercavernous sinus of each oestrous mare to sample pituitary venous blood and a second catheter was placed in the jugular vein. Continuous sampling ...
Shand N, Irvine CH, Turner JE, Alexander SL.Jugular blood samples were collected at 4 h intervals from six mares during an oestrous cycle to study the hormonal events that occur around the time of luteolysis. Blood samples from day 10 (day 0 = ovulation) until day 3 of oestrus were assayed for prostaglandin metabolite 13,14-dihydro-15-keto PGF2alpha (PGFM), oxytocin, prolactin, progesterone and oestrogen conjugates. PGF2alpha (0.5 or 1.5 mg) was administered to six mid-dioestrous mares and the oxytocin and prolactin responses were measured. One to five large (peak > or =2 x nadir) pulses of PGFM, oxytocin and prolactin were detected ...
Chavatte-Palmer P, Duchamp G, Palmer E, Ousey JC, Rossdale PD, Lombès M.Progesterone, oestrogen and glucocorticoid receptor concentrations in the uterus and mammary glands of pregnant mares during mid- to late gestation (from day 150 of gestation to term) were measured by binding assays to investigate the hormonal mechanisms involved in pregnancy maintenance and lactation. Uterine progesterone receptor concentrations did not increase significantly with increasing gestational age (from 67.8 +/- 13.7 to 126.1 +/- 48.7fmol mg(-1) protein), whereas oestrogen receptor concentrations were significantly higher in pregnant mares (271.7 +/- 28.9 fmol mg(-1) protein) than i...
Aurich C, Gerlach T, Aurich JE, Parvizi N.Modulation of reproductive functions is one of the multiple effects of growth hormone (GH). To investigate effects of reproductive functions on GH release in the horse, plasma GH concentrations in ovary-intact (n = 7) and ovariectomized (n = 8) mares during the anovulatory and breeding seasons and in pregnant mares (n = 6) at various stages of gestation were determined. To analyze an opioidergic regulation of GH release, repeated blood samples were taken over 3 h, and mares were injected with the opioid antagonist naloxone (0.5 mg/kg i.v.) or saline. GH was determined by RIA with an antiserum ...
Gastal EL, Bergfelt DR, Nogueira GP, Gastal MO, Ginther OJ.The effects of several doses of progesterone on FSH and LH concentrations were used to study the role of the gonadotropins on deviation in growth rates of the two largest follicles during the establishment of follicle dominance. Progesterone was given to pony mares at a daily dose rate of 0 mg (controls), 30 mg (low dose), 100 mg (intermediate dose), and 300 mg (high dose). All follicles > or = 6 mm were ablated at Day 10 (Day 0 = ovulation) to initiate a new follicular wave; prostaglandin F(2alpha) was given to induce luteolysis, and progesterone was given from Days 10 to 24. The low dose ...
Christman SA, Bailey MT, Wheaton JE, Troedsson MH, Ababneh MM, Santschi EM.To determine whether concentrations of dimeric inhibin (CaCA) are greater in plasma and tumor fluid from mares with granulosa-theca cell tumors (GTCT), compared with concentrations in plasma and equine follicular fluid (eFF) from control mares. Methods: 6 mares with GTCT and 12 clinically normal mares. Methods: The alphabetaA immunoradiometric assay used 2 antibodies, one against each subunit of inhibin (alpha and betaA subunits). Tumor tissue, tumor fluid, and a single blood sample were collected at the time of surgical removal of the GTCT. A single blood sample was collected from 7 control m...
Hoffmann B, Landeck A.To gain further information on gonadal function of the stallion, concentrations of testicular steroids in blood plasma (bpl) and seminal plasma (spl) and their distribution in the ejaculate were determined. Blood and semen samples from a total of 11 stallions were collected from November to July. Estrone (E1), estrone sulfate (E1S), estradiol-17beta (E2beta) and testosterone (T) were determined in bpl and spl, and in addition androstenedione (A), dehydroepiandrosterone (DHEA) and 5alpha-dihydrotestosterone (5alpha-DHT) were measured in spl. At certain points of time, aliquots of an ejaculate w...
Nagaoka K, Nambo Y, Nagamine N, Nagata SI, Tanaka Y, Shinbo H, Tsunoda N, Taniyama H, Watanabe G, Groome NP, Taya K.The relationship between a selective increase in circulating immunoreactive (ir)-inhibin and the time of ovulation was investigated in mares. Concentrations of plasma ir-inhibin were measured every 4 h during the periovulatory period. Inhibin pro-alphaC, a precursor protein of the inhibin alpha-subunit, was also measured. The changes in ir-inhibin and inhibin pro-alphaC in circulation were parallel. Concentrations of both ir-inhibin and inhibin pro-alphaC in the plasma increased at the same time when ovulatory follicles ruptured, and the peak levels of circulating ir-inhibin and inhibin pro-al...
Auvray P, Sourdaine P, Moslemi S, Séralini GE, Sonnet P, Enguehard C, Guillon J, Dallemagne P, Bureau R, Rault S.In this study, we describe the synthesis of a new family of indolizinone derivatives designed to fit an extrahydrophobic pocket within the active site of aromatase and to strongly inhibit human aromatase. This could help improve the specificity of the inhibitors. Equine aromatase, very well characterized biochemically, is used as a comparative model. Indeed, in a previous comparison between both human and equine aromatases, we described the importance of the interaction between the inhibitor and this pocket for the indane derivative MR 20814. MR 20492 and MR 20494 are more potent inhibitors of...
Boerboom D, Kerban A, Sirois J.Estradiol biosynthesis is a key biochemical trait of developing follicles. To study its regulation in equine follicles, the objectives of this study were to clone and determine the structure of equine cytochrome P450 aromatase (P450AROM), and characterize the regulation of P450AROM and P450 17alpha-hydroxylase/C17-20 lyase (P45017alpha) messenger RNAs (mRNAs) in vivo in equine preovulatory follicles isolated during hCG-induced ovulation. Two distinct P450AROM complementary DNAs (cDNAs) were isolated from an equine preovulatory follicle cDNA library. One clone was 2682 bp in length and included...
Henderson K, Stevens S, Bailey C, Hall G, Stewart J, Wards R.The relative merits of measuring blood concentrations of equine chorionic gonadotrophin (eCG, previously known as pregnant mare serum gonadotrophin (PMSG)), or oestrone sulphate (OS), or faecal OS concentrations for determining pregnancy status in miniature horses were investigated. Pregnant mares between 40 and 140 days after mating had serum eCG concentrations > 1 I.U. mL-1, with the highest concentrations occurring between days 50 and 120. However, eCG measurements were susceptible to returning a 'false positive' diagnosis of pregnancy. Plasma OS concentrations ranged from 0.1 to 3.6 ng ...
Popot MA, Lacabaratz E, Garcia P, Laroute V, Bonnaire Y, Toutain PL, Cowan DA.The cortisol threshold concentration of 1.0 microg/ml in horse urine adopted by the International Federation of the racing Authorities in 1994 is specific. However, an increase in the sensitivity for the detection of cortisol administration would be helpful. Previous studies have shown that 20beta-dihydrocortisol concentration in urine would be a good indicator of cortisol administration. The purpose of the present work was to estimate the population parameters and the critical values of 20beta-dihydrocortisol and 20beta-dihydrocortisone concentration in urine compared with that of cortisol. U...
Paccamonti DL, Pycock JF, Taverne MA, Bevers M, Van Der Weijden GC, Gutjahr S, Schams D, Blouin D.We investigated the half-life of oxytocin in reproductively normal mares and the prostaglandin response after oxytocin administrations. Mares were given oxytocin, 10 or 25 iu, i.v., on the day of, or 2 days after, ovulation, and frequent jugular blood samples were collected for analysis of oxytocin and Prostaglandin F metabolite (PGFM) by RIA. Neither dose of oxytocin nor day of treatment affected the half-life of the exogenous oxytocin, which was determined to be 6.8 min. A significant increase in PGFM was observed within 6 min of oxytocin administration and peak values were observed within 1...
Caloni F, Spotti M, Villa R, Mariani C, Montana M, Pompa G.An investigation was undertaken to demonstrate whether therapeutic treatment with ACTH raises hydrocortisone (cortisol) levels in horse urine above the limit (1000 ng/ml) established by the International Conference of Racing Authorities with the aim of controlling the abuse of cortisol and ACTH in equine sports. ACTH (200 iu) was administered i.m. to 3 Thoroughbred horses; urine and blood samples were collected at intervals afterwards and analysed by an immunoenzymatic system (ELISA) and HPLC-MS. To ascertain post exercise cortisol levels in untreated horses, 101 urine and 103 serum samples we...
Gastal EL, Gastal MO, Ginther OJ.A two-follicle model was used to study the nature of selection of the dominant follicle in mares by ablating neither or one of the two follicles on the day the larger follicle reached >/= 20 mm (Day 0). The larger follicle became the dominant follicle in all mares in which both follicles (n = 8) or only the larger follicle (n = 10) was retained. When only the smaller follicle (n = 9) was retained, it became dominant and ovulated in six mares and became atretic in three mares; the difference in diameter between the two follicles on Day 0 was less (p < 0.01) in mares in which the retained ...
Rigby S, Hill J, Miller C, Thompson J, Varner D, Blanchard T.It is probable that reduced pregnancy rates in mares bred to subfertile stallions is attributable, in part, to the reduced number of normal spermatozoa that colonize the oviduct. Administration of oxytocin stimulates both uterine and oviductal contractility. The hypothesis that oxytocin may enhance sperm transport to/into the oviducts, and thereby increase pregnancy rates, was tested in 2 trials. For both trials, fertile estrous mares with follicles > or = 35 mm in diameter were inseminated once at 24 h after administration of 1500 to 2000 U hCG. The inseminate dose was limited to 100 milli...
Chavatte-Palmer P, Arnaud G, Duvaux-Ponter C, Brosse L, Bougel S, Daels P, Guillaume D, Clément F, Palmer E.The induction of lactation is performed in ruminants by steroidogenic impregnation, followed by drugs intended to increase prolactin secretion. The aim of this study was to induce lactation in barren mares and to evaluate milk production. Five treated and 5 control mares were used in June and September in year 1, and 12 mares were used in year 2. Mares were administered a vaginal pessary (500 mg altrenogest and 50 mg estradiol benzoate) for 1 week. The 2nd week, another sponge with 100 mg estradiol benzoate was administered, together with 50 mg/100 kg body weight (BW) sulpiride in oil (IM q12h...
Besognet B, Hansen BS, Daels PF.We have previously demonstrated that daily administration of the dopamine D2 antagonist, sulpiride, during seasonal anoestrus, effectively advances the mean time of onset of the breeding season in mares. The purpose of this study was to examine the effect of sulpiride administration on pulsatile FSH and LH secretion in seasonally anoestrous mares, follicular development, time of first ovulation and the fertility at the first ovulation. Fourteen anoestrous mares were selected based on progesterone concentrations < 1 ng ml-1 for 3 weeks and largest follicle diameter < 20 mm. Starting 30 Ja...
Irvine CH, Alexander SL.To study the mechanisms responsible for the unusually slow decline of the ovulatory LH surge in mares, secretion patterns of GnRH, LH and FSH were monitored in pituitary venous blood collected every 2 or 5 min for 10.5-18.0 h from five mares on the third (n = 4) or fifth day after ovulation (first sampling period). To determine the effectiveness of progesterone negative feedback, mares were then given a luteolytic dose of a prostaglandin analogue (PGF2 alpha) and pituitary venous sampling (every 2 or 5 min for 16 h) recommenced 20-22 h later (second sampling period). During the declining arm o...
Villani M, Cairoli F, Kindahl H, Galeati G, Faustini M, Carluccio A, Veronesi MC.Very little information is available regarding the physiological mechanisms involved in the normal sexual activity in the stallion and, in particular, the endocrine control of reproduction is still not clearly understood. This experiment was designed to determine the short-term effect of sexual stimulation on plasma concentrations of testosterone, cortisol, oestrone sulphate and 15-ketodihydro-PGF(2alpha) in stallions. Semen samples were collected from 10 lighthorse stallions of proven fertility using a Missouri model artificial vagina. At the same time, blood samples were collected from the j...
Fazio E, Medica P, Cravana C, Ferlazzo A.In this study the effects of short distance road transport on total and free iodothyronine changes in 12 stallions (Equus asinus and Equus caballus) were evaluated. Donkeys (n = 6) and horses (n = 6) were transported for a distance of 50 km. Blood samples were collected 1 week before transport in basal conditions, 1 week later immediately before loading, and after transport and unloading. After transport, donkeys showed significant increases in circulating T4 (P≤0.01), fT3 (P≤0.001), and fT4 (P≤0.01) levels; while horses had significant increases in circulating T3, fT3 and fT4 (P≤0.01)...
Ginther OJ, Beg MA.The temporal associations of cortisol, estradiol-17β, and oxytocin with pulses of PGFM at the common hour of transition between preluteolysis and luteolysis was studied in plasma from hourly blood samples in mares (n=8). The transitional hour was determined from progesterone concentrations and occurred between 2PM and 2AM in all mares. Pulses of PGFM were grouped into those occurring at the last pulse of preluteolysis (preluteolytic pulse), at the hour of transition (transitional), and during luteolysis (luteolytic). The preluteolytic PGFM pulse (45±16pg/ml at peak) and transitional pulse (4...
Gastal MO, Pastorello M, Godoi DB, Gastal EL.The aim of this study was to compare the dominant follicle (DF) and gonadotropin dynamics for 9 days before ovulation in postpartum lactating (PP Lactating) versus non-postpartum cycling (N-PP Cycling) mares. Every PP Lactating mare on the day of parturition was paired with a N-PP Cycling mare, and the data analyses considered the partum-ovulation interval (POI) and the postpartum interovulatory interval (PPIOI) in PP Lactating mares and two interovulatory intervals in N-PP Cycling mares. The results of the present study revealed several novel and unique aspects of DF development and FSH and L...
Sato K, Miyake M, Yoshikawa T, Kambegawa A.Concentrations of progesterone and oestrogens were determined by radioimmunoassay in the peripheral blood of 22 Percheron and Breton breed mares from the 6th day of oestrus to the 150th day of pregnancy. Periodical variation patterns for the mean values of oestrone, oestradiol 17beta and total oestrogens in the cycling mares were found, with two peaks on the third day before and the 15th day after ovulation, and one depression on the 6th day of oestrus. In pregnant mares, the concentrations of oestrone and oestradiol 17beta increased rapidly (P less than 0.05) after Day 105 of gestation. Proge...
Slebodziński AB, Brzezińska-Slebodzińska E, Nowak J, Kowalska K.It is generally accepted that hormones and tissue growth factors are supplied from mother to neonate via mammary secretion. Among the protein hormones, insulin and prolactin are considered as the most important milk components for neonates. The significance of the thyroid hormones, namely triiodothyronine (T3) generated locally by 5'-monodeiodinase (5'-MD) in the mammary tissues, for the mammary gland itself and for suckling neonates is still under consideration. In the present study the activity of the 5'-MD and the concentrations of T3 and insulin in mare's colostrum and milk during the firs...
Jensen-Waern M, Lindberg A, Johannisson A, Gröndahl G, Lindgren JA, Essén-Gustavsson B.The effects of an endurance ride on neutrophil functions in endurance-trained horses were evaluated and related to metabolic changes and changes in cortisol concentrations. Blood samples were taken from 7 horses (aged 9-15 years) one day before, and then 30-60 min, 1 day and 8 days after the ride. The race resulted in elevated serum cortisol levels (< 465 nmol/l) and an increased neutrophil:lymphocyte ratio. Immediately post race, the neutrophil ability to engulf yeast was increased. One day after the race, a decrease in leukotriene B4 production (approximately 40%) and in the respiratory b...
Rambags BP, van Rossem AW, Blok EE, de Graaf-Roelfsema E, Kindahl H, van der Kolk JH, Stout TA.Insulin is a pancreatic hormone that classically regulates carbohydrate and fat metabolism, but also appears to play a role in various reproductive processes. A preliminary study suggested insulin production by day 10 to 18 equine conceptuses. The aim of the present study was to examine the hypothesis that insulin is the conceptus signal responsible for maternal recognition of pregnancy (MRP) in the mare, or otherwise influences reproductive cyclicity during the MRP period. Six Warmblood mares were treated daily during days 7 to 17 after ovulation of two successive oestrous cycles with either ...
Macan RC, Camargo CE, Zielinski BL, Cardoso NGH, de Lara NSS, Bergstein-Galan TG, Weiss RR, Kozicki LE.Timed artificial insemination (TAI) has boosted the use of conventional artificial insemination (CAI) by employing hormonal protocols to synchronize oestrus and ovulation. This study aimed to evaluate the efficiency of a hormonal protocol for TAI in mares, based on a combination of progesterone releasing intravaginal device (PRID), prostaglandin (PGF2α ) and human chorionic gonadotropin (hCG); and compare financial costs between CAI and TAI. Twenty-one mares were divided into two groups: CAI group (CAIG; n = 6 mares; 17 oestrous cycles) and TAI group (TAIG; n = 15 mares; 15 oestrous cycle...
Utt MD, Acosta TJ, Wiltbank MC, Ginther OJ.The acute effects of prostaglandin F(2alpha) (PGF) on circulating oxytocin and progesterone concentrations were characterized in mares during the mid- or late-luteal phase. Pony mares were randomly assigned to the following experimental groups based on treatment with PGF (2.5mg) or saline on Day 8 or Day 13 (Day 0=ovulation): PGF-8, PGF-13, saline-8, or saline-13 (n=7/group). Mares were fitted with indwelling, jugular vein catheters and two blood samples (-5 and 0 min) were collected prior to treatment. Treatments were administered into the jugular vein (0 min) and blood collection continued t...
Kaps M, Okada CTC, Gautier C, Aurich J, Scarlet D, Kuhl J, Aurich C.Behavior during the estrous cycle of mares can affect their performance and therefore inhibition of cyclical ovarian activity is indicated. We hypothesized that implants containing the GnRH analog deslorelin downregulate GnRH receptors and inhibit ovulation in mares. The estrous cycles of Shetland mares were synchronized with 2 injections of a PGF analog. One day after the second injection (day 0), mares received 9.4 (group D1, n = 6) and 4.7 mg deslorelin (D2, n = 5) as slow-release implants or 1.25 mg short-acting deslorelin as a control (C, n = 5). Ultrasonography of the reproductive trac...
Komosa M, Flisinska-Bojanowska A, Gill J.1. The development of diurnal rhythm activity of FDPA, AspAT and A1AT and in levels of cortisol, T3 and T4 was observed in the blood serum of six foals. 2. The studies began when a foal was 7 days old and were repeated every month until foals reached 1 year of age. Blood samples were taken every 4 hr for one day each month. 3. As a control group four barren mares were used, kept and examined in the same conditions. 4. In mature mares, diurnal rhythms in activity of A1AT (acrophase at 2200 hr), AspAt (2400 hr) and cortisol (0630 hr) but in T3 only in summer months (acrophase at 0100 hr) were ob...
Meyers PJ, Bowman T, Blodgett G, Conboy HS, Gimenez T, Reid MP, Taylor BC, Thayer J, Jöchle W, Trigg TE.In two separate controlled clinical trials, the efficacy and safety of 2.2 mg of the GnRH analogue deslorelin, administered subcutaneously as a short-term implant to normally cycling mares in oestrus with a dominant ovarian follicle more than 30 mm in diameter, were evaluated, using a placebo as a negative control. The oestrous cycle of each mare was followed by teasing, palpation per rectum and transrectal ultrasonography. Follicles were monitored every 24 hours by ultrasonography until ovulation occurred. The mares were either mated naturally or inseminated artificially. In trial 1, 174 mare...
Tortonese DJ, Preedy DF, Hesketh SA, Webb HN, Wilkinson ES, Allen WR, Fuller CJ, Townsend J, Short RV.Abrupt alterations in the 24-h light : dark cycle, such as those resulting from transmeridian air travel, disrupt circadian biological rhythms in humans with detrimental consequences on cognitive and physical performance. In the present study, a jetlag-simulated phase shift in photoperiod temporally impaired circadian peaks of peripheral clock gene expression in racehorses but acutely enhanced athletic performance without causing stress. Indices of aerobic and anaerobic capacities were significantly increased by a phase-advance, enabling prolonged physical activity before fatigue occurred. Thi...
Aurich C, Gerlach T, Aurich JE, Hoppen HO, Lange J, Parvizi N.In the non-breeding season, LH release is reduced via dopaminergic systems in the ram. On the other hand, our previous studies demonstrated an opioidergic inhibition of LH release in stallions outside the breeding season. Thus, in the present study we investigated the dopaminergic regulation of LH and prolactin secretion in stallions, considering interactions between dopamine and opioids. To achieve this, stallions (n=8) were treated with the dopamine antagonist sulpiride (0.6 mg/kg), the opioid antagonist naloxone (0.5 mg/kg), sulpiride plus naloxone or saline in December, March and June. Two...
O'Connor SJ, Fowden AL, Holdstock N, Giussani DA, Forhead AJ.Angiotensin-converting enzyme (ACE) has an active role in the control of blood pressure and body fluid homeostasis both before and after birth. This study investigated the ontogeny of pulmonary and renal ACE concentrations in fetal and neonatal horses. Fetal pulmonary ACE concentration increased from 250 days towards term (c. 335 days). Newborn foals showed significantly higher mean concentrations of pulmonary ACE (4.40 +/- 0.62 nmol min(-1) mg protein(-1)) than both fetuses during late gestation (1.23 +/- 0.51 nmol min(-1) mg protein(-1)) and animals aged 1 day to 2 weeks of postnatal age (0....
Watson ED, Bae SE, Thomassen R, Thomson SR, Woad K, Armstrong DG.The period between seasonal anoestrus and cyclicity is characterized in many mares by cyclical growth and regression of large dominant follicles. The insulin-like growth factor (IGF) system plays a key role in follicular growth and regression; therefore, we hypothesized that changes in the IGF system and its binding proteins would modulate onset of cyclicity in mares. Ovaries were obtained from pony mares on the day after detection of an actively growing 30 mm transitional anovulatory follicle, and also at the second or third oestrus of the breeding season on the day after the preovulatory fol...
Castro T, Jacob JC, Domingues RR, Ginther OJ.Prostaglandin E2 (PGE2) and prostaglandin F2α (PGF2α) are involved in equine embryo mobility throughout the uterus on Days 11-15 (ovulation = Day 0). On a day (Day 12) of maximal embryo mobility in pregnant mares (n = 13) and before luteolysis in nonbred mares (n = 10), gene expressions were compared between the uterine horns that did and did not contain the mobile embryo and between pregnant and nonbred mares. A cytobrush was used to collect an endometrial sample from the middle of each uterine horn. In nonbred mares, there was no difference for any of the considered gene expressions ...
Brown KA, Boerboom D, Bouchard N, Doré M, Lussier JG, Sirois J.17Beta-hydroxysteroid dehydrogenase type 4 (17betaHSD4) has a unique multidomain structure, with one domain involved in 17beta-estradiol inactivation. The objective of the study was to investigate the regulation of 17betaHSD4 during human chorionic gonadotropin (hCG)-induced ovulation/luteinization. The equine 17betaHSD4 cDNA was cloned and was shown to encode a 735-amino acid protein that is highly conserved (81-87% identity) compared with other mammalian orthologs. RT-PCR/Southern blot analyses were performed to study the regulation of 17betaHSD4 transcripts in equine preovulatory follicles ...
Jones I, Madej A.Microtitre plates were coated with antiserum against oestradiol-17 beta-6-(O-carboxymethyl)-oxime bovine serum albumin raised in sheep. The plasma samples (0.2-1.0 ml) were extracted with peroxide-free diethyl ether prepared daily by treatment with Al2O3. The enzyme conjugate was prepared by coupling oestradiol-17 beta-6-(O-carboxymethyl)-oxime to horse-radish peroxidase. The conjugate was chromatographed on a Sephadex G-25 column. The standard curve ranged from 0.37 to 18.40 fmol/well of oestradiol-17 beta. The amount of oestradiol-17 beta causing a 50% reduction of maximum binding was 4.4 fm...
Ababneh M, Ababneh H, Shidaifat F.Phospholipase A2 (PLA2) is a key enzyme for biosynthesis of PGF2α. Real-time RT-PCR and immunohistochemistry were used to determine transcription and cellular distribution of cytosolic PLA2 (cPLA2) in the equine endometrium during the oestrous cycle and early pregnancy. Endometrial biopsy and blood samples were collected from cycling mares on days (d) 8, 11, 15 and 18 (oestrus) (Day 0 = Day of ovulation; n = 5 for each day) and from pregnant mares (n = 4) on d15. Except for mares on d18 and some cyclic mares (n = 2) on d15 with low progesterone (P₄) concentrations (< 3.18 nm), P₄ conce...
Bousfield GR, Liu WK, Ward DN.LH hybrids were prepared by combining eLH alpha and eLH beta with the corresponding subunits of oLH, pLH and hCG. Recombinants were isolated by gel filtration and assessed by SDS-polyacrylamide gel electrophoresis under both dissociating and non-dissociating conditions. All combinations of subunits produced hybrid LH molecules. Hybrids prepared by combining eLH beta with oLH alpha, pLH alpha or hCG alpha were very inactive in rat radioligand and Leydig cell in vitro bioassays. Hybrids prepared with eLH alpha were very active in both assays. The greatest potentiating activity was observed when ...
Richard F, Martinat N, Remy JJ, Salesse R, Combarnous Y.Among all mammalian FSH receptors (FSH-R; including donkey (dk) FSH-R), only horse (hs) FSH-R does not bind hsLH/chorionic gonadotrophin (CG). In order to delineate the structural origin of hsFSH-R specificity precisely, we have cloned dkFSH-R cDNA from donkey testis mRNA by RT-PCR. Transiently expressed dkFSH-R endowed COS-7 cells with both hsLH/CG- and FSH-binding activity, as well as FSH-induced cAMP production. The deduced dkFSH-R amino acid sequence shares 96% identity with the hsFSH-R: notably, in the hormone-binding domain, the specificity of hsFSH-R may be ascribed to only four diverge...
Saint-Dizier M, Foulon-Gauze F, Lecompte F, Combarnous Y, Chopineau M.Pituitary equine luteinizing hormone (eLH) and fetal chorionic gonadotrophin (eCG) have identical polypeptidic chains, but different linked carbohydrates. In equine tissues, eCG and eLH bind only to the LH/CG receptor (eLH/CG-R) and have no FSH activity. However, radio-receptor assays on equine luteal or testicular tissues have shown that eCG binds to the eLH/CG-R with only 2-4% of the binding activity of eLH. In order to study the structure-function relationship of eLH and eCG in a homologous system, we undertook the cloning and functional expression of the eLH/CG-R. Based on sequence homolog...
Squires EL, McKinnon AO, Carnevale EM, Morris R, Nett TM.For embryos collected from mares 7 days after ovulation, embryo recovery for single-ovulating mares was 53% compared to 106% for double-ovulating mares. Pregnancy rates 50 days after surgical transfer were 68 and 129%, respectively. Concentrations of LH were similar during the periovulatory period for cycles which included single or double ovulations. Horse pituitary extract given for 5.5 days resulted in greater than or equal to 2 ovulations (mean 3.8) in 26 of 28 mares and 2.0 embryos were recovered per donor compared to 0.65 for controls. Non-surgical pregnancy rates for embryos collected f...
Sechin A, Deschamps JC, Lucia T, Aleixo JA, Bordignon V.We evaluated the effect of PMSG on the weaning-to-first service interval, total litter size and born alive litter size in swine. Four doses of PMSG (0, 500, 750 and 1,000 IU) were administered intramuscularly after weaning to sows at 3 different farms, grouped by parities (1, 2 and 3 or higher) and 2 distinct time periods. The associations among main effects and response variables were assessed by analysis of variance. Polynomial orthogonal terms were used to adjust the estimates of weaning-to-first service interval, total litter size and born alive litter size for the interaction effect of pa...
