The endocrine system in horses comprises a network of glands and hormones that regulate various physiological processes, including metabolism, growth, reproduction, and stress response. Key components of the equine endocrine system include the pituitary gland, thyroid gland, adrenal glands, and pancreas. Hormones such as insulin, cortisol, and thyroid hormones are produced and released into the bloodstream to maintain homeostasis and respond to internal and external stimuli. Dysregulation of the endocrine system can lead to conditions such as Equine Cushing's Disease (Pituitary Pars Intermedia Dysfunction) and Equine Metabolic Syndrome. This page compiles peer-reviewed research studies and scholarly articles that explore the structure, function, and disorders of the endocrine system in horses, providing insights into its impact on equine health and management.
Held F, Ekstrand C, Cvijovic M, Gabrielsson J, Jirstrand M.Cortisol is a steroid hormone relevant to immune function in horses and other species and shows a circadian rhythm. The glucocorticoid dexamethasone suppresses cortisol in horses. Pituitary pars intermedia dysfunction (PPID) is a disease in which the cortisol suppression mechanism through dexamethasone is challenged. Overnight dexamethasone suppression test (DST) protocols are used to test the functioning of this mechanism and to establish a diagnosis for PPID. However, existing DST protocols have been recognized to perform poorly in previous experimental studies, often indicating presence of ...
Cassimeris L, Engiles JB, Galantino-Homer H.Laminitis is often associated with endocrinopathies that cause hyperinsulinemia and is also induced experimentally by hyperinsulinemia, suggesting that insulin initiates laminitis pathogenesis. Hyperinsulinemia is expected to activate pro-growth and anabolic signaling pathways. We hypothesize that chronic over-stimulation of these pathways in lamellar tissue results in endoplasmic reticulum stress, contributing to tissue pathology, as it does in human metabolic diseases. We tested this hypothesis by asking whether lamellar tissue from horses with naturally-occurring endocrinopathic laminitis s...
Mejia-Pereira S, Perez-Ecija A, Buchanan BR, Toribio RE, Mendoza FJ.Endocrine disorders are common in donkeys. Pituitary pars intermedia dysfunction (PPID) is thought to be a frequent disturbance in donkeys due to their longevity. However, information on PPID dynamic testing in donkeys is lacking. Objective: The objective of this study was to evaluate the previously described guidelines for PPID diagnosis in horses in donkeys with suspicion of PPID. Methods: Prospective experimental study. Methods: Eighty donkeys were evaluated for PPID suspicion based on clinical signs and baseline adrenocorticotropic hormone (ACTH) concentrations. Six mix-breed donkeys (one ...
Durward-Akhurst SA, Schultz NE, Norton EM, Rendahl AK, Besselink H, Behnisch PA, Brouwer A, Geor RJ, Mickelson JR, McCue ME.Equine Metabolic Syndrome (EMS) is characterized by abnormalities in insulin regulation, increased adiposity and laminitis, and has several similarities to human metabolic syndrome. A large amount of environmental variability in the EMS phenotype is not explained by commonly measured factors (diet, exercise, and season), suggesting that other environmental factors play a role in EMS development. Endocrine disrupting chemicals (EDCs) are associated with metabolic syndrome and other endocrine abnormalities in humans. This led us to hypothesize that EDCs are detectable in horse plasma and play a ...
Kornicka K, Śmieszek A, Węgrzyn AS, Röcken M, Marycz K.Endocrine disorders, including equine metabolic syndrome (EMS), are a serious issue in veterinary medicine and horse breeding. Furthermore, EMS was shown to affect the cytophysiological properties of adipose-derived stem cells, reducing their therapeutic potential. However, it was shown that those cells can be rejuvenated while using a combination of two chemicals: 5-azacytydine (AZA) and resveratrol (RES). In the present study, we decided to evaluate the immunomodulatory properties of AZA/RES-treated adipose-derived stem cells (ASC) isolated from EMS horses (ASC). Thus, we co-cultured ASC wit...
Kornicka K, Śmieszek A, Szłapka-Kosarzewska J, Irwin Houston JM, Roecken M, Marycz K.Endocrine disorders are becoming an increasing problem in both human and veterinary medicine. In recent years, more and more horses worldwide have been suffering from equine metabolic syndrome (EMS). This metabolic disorder is characterized by pathological obesity, hyperinsulinaemia, hyperglycaemia and insulin resistance. Although metabolic disorders, including diabetes, have been extensively studied, there are still no data on the molecular effects of EMS in horses. Thus, the aim of this study was to evaluate apoptosis, oxidative stress, autophagy and microRNA (miR) expression in multipotent ...
Ball BA, Davolli GM, Esteller-Vico A, Fleming BO, Wynn MAA, Conley AJ.The biological function of inhibin is mediated by two heterodimers, inhibin-A and inhibin-B. The relative importance of inhibin-A and -B in male reproductive function varies considerably across species with inhibin-B predominating in many species, whereas inhibin-A appears relatively more important in rams. Research reported to date in stallions has examined total or immunoreactive (ir) inhibin which does not distinguish the two heterodimers. Therefore, the objective of this study was to characterize changes in inhibin-A and inhibin-B concentrations in stallions: 1) across season for a period ...
Satué K, Marcilla M, Medica P, Ferlazzo A, Fazio E.Androgens modulate maternal ovarian activity, embryo implantation and correct placental development. The objective of this study was to establish reference values for testosterone (T), androstenedione (A4) and dehydroepiandrosterone (DHEA) concentrations in pregnant mares. A total of 30 healthy Spanish Purebred mares with an age range of 9.33 ± 3.31 years, were studied during the 11 months of gestation. T, A4 and DHEA concentrations were determined using EIA validated specifically for equines. T increased in the 2nd and 3rd month (P < 0.05), showing a plateau between the 4th and 6th m...
Mendoza FJ, Gonzalez-Cara CA, Aguilera-Aguilera R, Toribio RE, Perez-Ecija A.Metabolic disorders are highly prevalent in donkeys. Differences in energy regulatory hormones and glucose dynamic testing, including the intravenous glucose tolerance test (IVGTT) and combined glucose-insulin test (CGIT), have been documented between donkeys and horses. The aims of this study were to characterise the insulin:glucagon (IGR) and glucagon:insulin (GIR) molar ratios, at baseline and in response to the IVGTT and CGIT in healthy donkeys, and to determine their correlation with endocrine (leptin, ghrelin and adiponectin) and morphometric variables. Median values and interquartile ra...
Coleman MC, Belknap JK, Eades SC, Galantino-Homer HL, Hunt RJ, Geor RJ, McCue ME, McIlwraith CW, Moore RM, Peroni JF, Townsend HG, White NA....OBJECTIVE To investigate risk factors for the development of pasture- and endocrinopathy-associated laminitis (PEAL) in horses and ponies in North America. DESIGN Case-control study. ANIMALS 199 horses with incident cases of PEAL and 351 horses from 2 control populations (healthy horses [n = 198] and horses with lameness not caused by laminitis [153]) that were evaluated in North America between January 2012 and December 2015 by veterinarian members of the American Association of Equine Practitioners. PROCEDURES North American members of the American Association of Equine Practitioners were co...
Byrne DP, Secombe CJ, Tan RHH, Perera DI, Watts SP, Wearn JG.Thyrotropin releasing hormone (TRH)-stimulation testing for pituitary pars intermedia dysfunction (PPID) in horses is only recommended at certain times of the year. Current diagnostic cut-off values reflect testing in the northern hemisphere during this time. The aims of this study were to evaluate TRH stimulation testing during two different phases of the circannual pituitary cycle and to determine whether diagnostic cut-off values developed in the northern hemisphere are appropriate in Australia. Thirteen clinically normal horses at Perth, Western Australia, and 23 horses at Townsville, Quee...
Lewis SL, Holl HM, Long MT, Mallicote MF, Brooks SA.Equine metabolic syndrome (EMS), like human metabolic syndrome, comprises a collection of clinical signs related to obesity, insulin dysregulation and susceptibility to secondary inflammatory disease. Although the secondary conditions resulting from EMS can be life-threatening, diagnosis is not straightforward and often complicated by the presence of other concurrent conditions like pituitary pars intermedia dysfunction (PPID). In order to better characterize EMS, we sought to describe the variation within, and correlations between, typical physical and endocrine parameters for EMS. Utilizing ...
Marycz K, Kornicka K, Irwin-Houston JM, Weiss C.Endocrine disorders have become more and more frequently diagnosed in humans and animals. In horses, equine metabolic syndrome (EMS) is characterized by insulin resistance, hyperleptinemia, hyperinsulinemia, inflammation and usually by pathological obesity. Due to an increased inflammatory response in the adipose tissue, cytophysiological properties of adipose derived stem cells (ASC) have been impaired, which strongly limits their therapeutic potential. Excessive accumulation of reactive oxygen species, mitochondria deterioration and accelerated ageing of those cells affect their multipotency...
Müller V, Curcio BR, Toribio RE, Feijó LS, Borba LA, Canisso IF, Nogueira CEW.This study aimed to evaluate steroid hormones in foals born from mares treated for ascending placentitis with different combinations of trimethoprim-sulfamethoxazole (TMS), flunixin meglumine (FM), long-acting altrenogest (ALT) and estradiol cypionate (ECP) for ten consecutive days, starting two days after experimental induction of placentitis with Streptococcus zooepidemicus. Fourty-six pregnant mares and respective foals were assigned as healthy group (Control, n = 8) or treated groups as follows: TMS+FM (n = 8), TMS+FM+ALT (n = 8), TMS+FM+ALT+ECP (n = 6), TMS+FM+ECP (n = 6) and no...
Nacarino-Meneses C, Köhler M.The annual cyclicality of cortical bone growth marks (BGMs) allows reconstruction of some important life history traits, such as longevity, growth rate or age at maturity. Little attention has been paid, however, to non-cyclical BGMs, though some record key life history events such as hatching (egg-laying vertebrates), metamorphosis (amphibians), or weaning (suggested for Microcebus and the hedgehog). Here, we investigate the relationship between non-cyclical BGMs and a stressful biological event in mammals: the moment of birth. In the present study, we histologically examine ontogenetic serie...
Tadros EM, Fowlie JG, Refsal KR, Marteniuk J, Schott HC.Hyperinsulinaemia is the suspected component of insulin dysregulation having the strongest association with laminitis and occurs variably in equids with pituitary pars intermedia dysfunction (PPID). Objective: We hypothesised that magnitude of hyperinsulinaemia correlates with laminitis severity in PPID-affected equids. Furthermore, we hypothesised that owners can be unaware of chronic endocrinopathic laminitis. Methods: Cross-sectional study. Methods: Serum insulin concentrations, owner-reported laminitis history and radiographic evidence of laminitis were determined in 38 client-owned horses...
Shotton JCR, Justice WSM, Salguero FJ, Stevens A, Bacci B. Pituitary pars intermedia dysfunction (PPID), also known as equine Cushing's disease, is widely reported in middle-aged to older domestic equids but to date reported in only one nondomestic equid, the onager ( Equus hemionus onager). This case series reports clinical, hematological, and pathological findings consistent with PPID in two further equid species: one Chapman's zebra ( Equus quagga chapmani) and five Przewalski's horses ( Equus ferus przewalskii). The case series reports basal adrenocorticotropic hormone (ACTH) testing as a method to diagnose and monitor PPID in zoological equid...
Nanayakkara SN, Rahnama S, Harris PA, Anderson ST, de Laat MA, Bailey S, Sillence MN.Although it is well established that equine laminitis can be triggered by extreme hyperinsulinemia, the mechanism of insulin action is not known. High concentrations of insulin lead to separation of the weight-bearing apparatus from the hoof wall and are associated with an increased cycle of cell death and proliferation in the lamellae. Gene expression and immunohistochemistry studies have indicated that the lamellae are sparsely populated with insulin receptors, whereas IGF-1 receptors (IGF-1R) are abundant, suggesting that the action of insulin may be mediated by insulin binding to the IGF-1...
Secombe CJ, Bailey SR, de Laat MA, Hughes KJ, Stewart AJ, Sonis JM, Tan R.The purpose of this article is to provide a review of the current knowledge and opinions about the epidemiology, clinical findings (including sequelae), diagnosis, treatment and monitoring of equine pituitary pars intermedia dysfunction, particularly in the Australian context. This information and the recommendations provided will assist practitioners in making informed decisions regarding the diagnosis and management of this disorder.
Conley AJ, Scholtz EL, Legacki EL, Corbin CJ, Knych HK, Dujovne GD, Ball BA, Moeller BC, Stanley SD. and evidence indicates that the bioactive, 5α-reduced progesterone metabolite, 5α-dihydroprogesterone (DHP) is synthesized in the placenta, supporting equine pregnancy, but its appearance in early pregnancy argues for other sites of synthesis also. It remains unknown if DHP circulates at relevant concentrations in cyclic mares and, if so, does synthesis involve the non-pregnant uterus? Jugular blood was drawn daily from cyclic mares ( = 5). Additionally, ovariectomized mares (OVX) and geldings were administered progesterone (300 mg) intramuscularly. Blood was drawn before and after t...
Satué K, Marcilla M, Medica P, Cravana C, Fazio E.Growth hormone (GH) and insulin-like growth factor (IGF-I) exert essential functions to maintain an adequate metabolic activity for correct placental and fetal development. Although fructosamine (FRUCT) is used in clinical evaluation to assess the glycaemic state, the relationships between GH, IGF-I and FRUCT remain unknown in the mare. Therefore, the objectives of this study were to evaluate the relationships among these parameters in pregnant mares. A total of 30 healthy Spanish Purebred mares, with an age range of 9.33 ± 3.31 years, were studied during the 11 months of gestation. Serum...
Frank N.Equine athletes are affected by 2 major endocrine/metabolic disorders, insulin dysregulation (ID) and pituitary pars intermedia dysfunction. ID is a risk factor for laminitis in horses, which poses the greatest threat to performance because of the damage that it causes to hoof structures. This article includes an in-depth discussion of ID and other risk factors for laminitis that are grouped together as equine metabolic syndrome. As horses age, the risk of pituitary pars intermedia dysfunction increases, and this endocrine disorder may exacerbate preexisting ID and further increase the risk of...
Menzies-Gow NJ, Knowles EJ, Rogers I, Rendle DI.Circulating adiponectin concentrations were lower in ponies with a history of endocrinopathic laminitis and in nonlaminitic ponies that subsequently developed laminitis. The assays used in these studies have been discontinued or are no longer valid. Objective: (1) to determine the validity of immunoturbidimetric (IT) and enzyme linkedimmunosorbent (ELISA) assays for equine total and high molecular weight (HMW) [adiponectin] measurement and (2) to investigate the association between [adiponectin] measured using these assays and endocrinopathic laminitis. Methods: Method validation and cohort st...
Sauer FJ, Bruckmaier RM, Ramseyer A, Vidondo B, Scheidegger MD, Gerber V.The aims of this study were to better characterize the adrenal response to i.v. adrenocorticotropic hormone (ACTH) in horses with and without gastric disease and to validate and simplify the ACTH stimulation test by determining the diagnostic accuracy of six consecutive sampling time points after ACTH administration for equine glandular gastric disease (EGGD) and equine squamous gastric disease (ESGD). Twenty-six endurance and eventing horses without clinical disease [Sport Horse Population (SHP)] and an independent population of 62 horses [General Population (GP)] were grouped by gastroscopic...
Ellerbrock RE, Canisso IF, Lima FS, Shipley CF, Thompson DL, Conley AJ, Kline KH.The objectives of this study were to determine the concentrations of reproductive and metabolic hormones during the peripubertal period and to assess their relationship with testicular development and body fat deposition. Blood samples were collected from 23 healthy Standardbred colts every four weeks for twelve months. Colts were weighed monthly, and percent of body fat and testicular volume estimated by ultrasound. Onset of puberty was determined as the month when testosterone was two standard deviations above the previous mean. Plasma FSH, LH, leptin, estradiol-17β, androstenedione, IGF-1,...
Bertin FR, Ruffin-Taylor D, Stewart AJ.Systemic inflammation is a cause of insulin dysregulation in many species, but the insulin and glucose dynamics in adult horses diagnosed with systemic inflammatory response syndrome (SIRS) are poorly documented. Objective: In SIRS in horses, insulin and glucose dynamics will be altered and associated with survival. Methods: Adult horses diagnosed with SIRS admitted to a referral hospital. Methods: Prospective study enrolling horses diagnosed with SIRS in which serum insulin and glucose concentrations were measured. Horses were grouped by outcome (survival, hyperinsulinemia, and hyperglycemia)...
Breuhaus BA.With more horses remaining active longer in life, it is important to characterize changes that occur normally with aging, so that these can be differentiated from development of disease. The objective of the study was to test the hypotheses that geriatric horses have lower circulating concentrations of thyroid hormones and/or higher serum thyrotropin (TSH) concentrations compared to younger horses. Serum thyroid hormone and TSH concentrations from 71 normal, healthy horses that had participated in prior research projects were analyzed for effects of age, sex, and season when samples were obtai...
Oberhaus EL, Thompson DL, Foster BA, Pinto CR.This experiment assessed the hormonal production, secretory aspects, and changes in luteinizing hormone (LH) receptor gene expression of early induced ovulatory-sized follicles relative to the first ovulatory-sized follicles occurring naturally in the spring. Anovulatory mares were treated on January 21 with (1) 50 mg of estradiol cypionate (ECP, n = 8) alone or (2) with ECP followed by two 3-g sulpiride injections (n = 8), 5 and 12 days later. Half of each group also received complete follicle ablation via transvaginal aspiration before ECP treatment. Ovaries were scanned regularly until ...
Dybdal NO, Hargreaves KM, Madigan JE, Gribble DH, Kennedy PC, Stabenfeldt GH.Pituitary pars intermedia dysfunction is a slowly progressive disorder that afflicts most breeds of horses. Because it shares features with human Cushing disease, it has been referred to as equine Cushing disease. A variety of tests of pituitary-adrenocortical function were performed on horses with evidence of pituitary pars intermediate dysfunction, and results were compared with those in healthy control horses. Diurnal variations in plasma cortisol concentration were not statistically different between control horses and those with pituitary pars intermedia dysfunction. An ACTH stimulation (...
McFarlane D, Paradis MR, Zimmel D, Sykes B, Brorsen BW, Sanchez A, Vainio K.Plasma α-melanocyte-stimulating hormone (α-MSH) and adrenocorticotropin (ACTH) concentrations in horses vary with season, confounding diagnostic testing for pituitary pars intermedia dysfunction (PPID). Objective: The goals of this study were to determine whether seasonal variation in plasma α-MSH and ACTH concentrations in horses is influenced by geographic location, breed, or PPID. Methods: Healthy light breed horses residing in Florida, Massachusetts, and Finland (n = 12 per group); healthy Morgan horses (n = 13); healthy ponies (n = 9) and horses with PPID (n = 8). Methods: Monthly plas...
Call GB, Wolfe MW.Activation of the luteinizing hormone beta (LHbeta) promoter by gonadotropin-releasing hormone (GnRH) via the transcription factor early growth response protein-1 (Egr1) has been well characterized. To determine the mechanisms affecting Egr1 regulation of LHbeta, we analyzed five different species of LHbeta promoters (equine, mouse, rat, bovine and human). Electrophoretic mobility shift assays (EMSAs) identified multiple transcription factors binding to the Egr regions on the LHbeta promoter. Species-specific differences existed in the binding affinity for Sp1, Sp3, steroidogenic factor-1 (SF-...
Nagata S, Takeda F, Kurosawa M, Mima K, Hiraga A, Kai M, Taya K.The responses of plasma adrenocorticotropin (ACTH), cortisol, noradrenaline and adrenaline in 5 Thoroughbred horses to an incremental exercise and 2 relative workload exercises, at 105 and 80% maximal oxygen consumption (VO2max), on a treadmill were examined. These hormone concentrations increased (P < 0.05) with each exercise and the maximal plasma concentrations of ACTH, cortisol were observed between 5 and 30 min after the end of the exercise, while maximal catecholamine concentrations occurred just at exhaustion time. The plasma ACTH, noradrenaline and adrenaline responses during exerci...
SHORT RV.A comparison has been made between the steroids present in equine follicular fluid and luteal tissue. Follicular fluid was found to contain progesterone, 17α-hydroxyprogesterone, androstenedione, epitestosterone, 19-norandrostenedione, oestrone, oestradiol-17β and 6α-hydroxyoestradiol-17β, in confirmation of previous studies. On the other hand, luteal tissue contained large amounts of progesterone and 20α-hydroxypregn-4-en-3-one, and a small quantity of 17α-hydroxyprogesterone. No C18 or C19 steroids could be detected.
These findings are therefore interpreted as evidence in favour of ...
Hart KA, Dirikolu L, Ferguson DC, Norton NA, Barton MH.To compare daily endogenous cortisol production rate and the pharmacokinetics of an i.v. bolus of hydrocortisone between neonatal foals and adult horses. Methods: 10 healthy full-term 2- to 4-day-old foals and 7 healthy adult horses. Methods: Blood samples were collected from each horse every 15 to 20 minutes for 24 hours for determination of 24-hour mean cortisol concentration. Afterward, dexamethasone (0.08 mg/kg) was administered i.v. to suppress endogenous cortisol production. Twelve hours afterward, hydrocortisone sodium succinate (1.0 mg/kg) was administered as a rapid i.v. bolus and ser...
Hoffsis GF, Murdick PW, Tharp VL, Ault K.The plasma concentration of cortisol and corticosterone in the normal horse was determined by competitive protein-binding analysis (radiostereoassay). The mean plasma concentration of the 2 steroids in resting horses was 5.12 μg./ml., with standard deviation of 1.67 μg. There were no significant differences in the mean values according to age, sex, and pregnancy. Seemingly, diurnal variations in concentrations of the steroids existed in horses; values were high in the morning and low in the evening. Plasma values were increased in horses given corticotropin (acth) and were decreased in those...
Almeida J, Conley AJ, Mathewson L, Ball BA.In the mammalian testis, Leydig cells are primarily responsible for steroidogenesis. In adult stallions, the major endocrine products of Leydig cells include testosterone and estrogens. 3β-hydroxysteroid dehydrogenase/Δ(5)-Δ(4)-isomerase (3βHSD) and 17α-hydroxylase/17,20-lyase (P450c17) are two key steroidogenic enzymes that regulate testosterone synthesis. Androgens produced by P450c17 serve as substrate for estrogen synthesis. The aim of this study was to investigate localization of the steroidogenic enzymes P450c17, 3βHSD, and P450arom and to determine changes in expression during dev...
Cartmill JA, Thompson DL, Storer WA, Gentry LR, Huff NK.Previous observations from this laboratory indicated that horses with high BCS could have resting plasma leptin concentrations ranging from low (1 to 5 ng/mL) to very high (10 to 50 ng/mL). To study the possible interactions of leptin secretion with other endocrine systems, BCS and plasma leptin concentrations were measured on 36 mares and 18 geldings. From mares and geldings that had a mean BCS of at least 7.5, five with the lowest (low leptin) and five with the highest (high leptin) leptin concentrations were selected. Jugular blood samples were collected twice daily for 3 d from the 20 sele...
Funk RA, Wooldridge AA, Stewart AJ, Behrend EN, Kemppainen RJ, Zhong Q, Johnson AK.Equine metabolic syndrome (EMS) is an increasingly recognized problem in adult horses. Affected horses are often obese and predisposed to the development of laminitis, especially in the spring and summer months. In addition, in the summer and fall months, increases in endogenous insulin concentrations, a marker of EMS, have been reported. Objective: The purpose of this study was to evaluate seasonal changes in results of the combined glucose-insulin tolerance test (CGIT), a diagnostic test for EMS. Methods: Nine healthy, aged horses with no history of laminitis and no clinical signs of EMS. Me...
Almeida J, Conley AJ, Mathewson L, Ball BA.Sertoli cells are essential in development of a functional testis. During puberty, Sertoli cell maturation can be characterized by a number of markers, including anti-Müllerian hormone (AMH) and its receptor (AMHR2), androgen receptor (AR), cyclin-dependent kinase inhibitor (CDKN1B), and connexin 43 (Cx43). In the present study, immunohistochemistry (IHC) and real-time quantitative polymerase chain reaction (RT-qPCR) were used to characterize changes in expression of AMH, AMHR2, AR, CDKN1B, and Cx43 in prepubertal, postpubertal, and adult equine testes. During puberty, AMH expression decrease...
Scheidegger MD, Gerber V, Ramseyer A, Schüpbach-Regula G, Bruckmaier RM, van der Kolk JH.The aim of this study was to further characterize the ACTH stimulation test as reflected by salivary cortisol response and to measure the short- and long-term repeatability of it in healthy horses as a tool to assess the capacity of the adrenal cortex to secrete cortisol. Nineteen healthy horses were subjected to 3 ACTH stimulation tests. Intervals were 2 wk and 5 mo between the first and second and the second and third tests, respectively. A dose of 1-μg/kg BW synthetic ACTH was injected intravenously. Saliva samples were collected at baseline and at 30, 60, 90, 120, 150, and 180 min afte...
Sauer FJ, Gerber V, Frei S, Bruckmaier RM, Groessl M.The aim of the present study was to measure salivary cortisol concentrations of horses before and after hypothalamic-pituitary-adrenal (HPA) axis stimulation by means of liquid chromatography-tandem-mass spectrometry (LC-MS/MS) and an immunoassay (cELISA) for method comparison. Nine clinically healthy horses participated in the study. An ACTH stimulation test was performed. Saliva samples were collected before (T0) and 60 (T60) min after intravenous injection of 1 μg/kg BW synthetic ACTH1-24. LC-MS/MS was assessed for the determination of equine salivary cortisol. The results of these measur...
Blikslager AT.Management factors associated with colic, particularly related to stall confinement and nutrition, have been linked to alterations in gastrointestinal mucosal transport, motility, and microbiome, which in turn creates conditions that induce colic. In particular, meal feeding creates large changes in water movement in and out of the colon and alters the microbiome. These conditions may in turn result in colic conditions such as large colon impaction or large colon volvulus. In addition, a range of management and nutritional factors have been found to place horses at risk of select colic conditi...
Barsnick RJ, Hurcombe SD, Smith PA, Slovis NM, Sprayberry KA, Saville WJ, Toribio RE.Endocrine dysregulation of hormones of energy metabolism is well documented in critically ill humans, but limited information exists in septic foals. The purpose of this study was to provide information on the hormonal response to energy metabolism in critically ill foals, focusing on insulin, glucagon, and leptin. Objective: Concentrations of insulin, glucagon, leptin, and triglycerides will be higher, whereas glucose concentration will be lower in septic foals than in healthy and sick nonseptic foals. The magnitude of these differences will be associated with severity of disease and nonsurvi...
Silver M, Fowden AL.The present study was carried out on 19 chronically catheterized mares and fetuses in late gestation (term > 320 days). In six animals which were monitored up to the time of delivery of a live foal, plasma and amniotic fluid cortisol concentrations remained low until 4-5 days before parturition when there was a rapid, significant rise (P < 0.05) which was not accompanied by any corresponding changes in maternal plasma cortisol. Circulating fetal ACTH concentrations became more variable close to delivery and ANOVA revealed no significant increases during this critical period, although a n...
Jellyman JK, Valenzuela OA, Fowden AL.Adrenal glucocorticoids, such as cortisol, are essential for normal fetal development and for maintaining homeostasis in adults. Developmental studies in humans and other animals have shown that exposure to excess glucocorticoids during critical windows of perinatal development can program permanent changes in hypothalamic-pituitary-adrenal (HPA) axis function and metabolic function, with adverse implications for the long-term health of the exposed offspring. The current review compares the programming of postnatal HPA axis function and glucose homeostasis among different species overexposed p...
Fowden AL, Forhead AJ, Ousey JC.Delivery of viable young requires co-ordination of fetal maturation with the onset of labour at term. In turn, this depends on a cascade of fetal and maternal endocrine events. The sequence of these events is broadly similar in most mammals but there are differences in placental hormone synthesis and in the timing and magnitude of key prepartum endocrine changes between species. In most farm animals, maternal progesterone (P4) levels decline and oestrogen levels increase in the last 5 - 10 days before delivery in response to activation of the fetal hypothalamicpituitary-adrenal (HPA) axis and ...
Rendle DI, Litchfield E, Heller J, Hughes KJ.There is little published information on whether measurement of plasma ACTH concentration at a single timepoint is a repeatable indicator of pituitary pars intermedia dysfunction (PPID). Objective: To determine whether ultradian or circadian fluctuations in ACTH production influence plasma ACTH concentration in normal horses and horses with PPID. Methods: Prospective observational study. Methods: Plasma ACTH concentration in 8 non-PPID horses and 8 horses with PPID was measured at 08.00, 11.00, 14.00 and 17.00 h on 5 nonconsecutive days within a 3 week period. In addition, at 08.30 h on one da...
Beech J, McFarlane D, Lindborg S, Sojka JE, Boston RC.To compare endogenous ACTH and α-melanocyte-stimulating hormone (α-MSH) concentrations after administration of thyrotropin-releasing hormone (TRH) and to compare ACTH concentrations after TRH administration with those following domperidone administration in healthy horses and horses with pituitary pars intermedia dysfunction (PPID). Methods: Prospective case series. Methods: 69 clinically normal horses and 47 horses with or suspected to have PPID. Methods: ACTH concentrations were measured during 108 TRH stimulation tests in 88 horses, and α-MSH concentrations were measured during 56 TRH st...
Crowell-Davis SL.The mare is seasonally polyestrus, having an anovulatory period during the short light days of late fall and early winter, and beginning to ovulate as the days become longer during the winter. The complete estrus cycle is typically about 3 weeks, with 5 to 7 days of estrus and approximately 2 weeks of diestrus. When a mare lives within the natural social structure of the horse, i.e. a family band with several adult mares and one or more stallions, estrus is characterized by repeatedly approaching the stallion, frequent urination, deviating the tail away from the perineum, and standing still wi...
Al-zi'abi MO, Watson ED, Fraser HM.Precise pharmacological control of the corpus luteum is important in the manipulation of the oestrous cycle in mares. Angiogenesis plays a key role in the growth and regression of the corpus luteum; therefore, influencing the vasculature of the corpus luteum may offer a novel method for controlling its lifespan. In the present study, changes in angiogenesis and vascular expression of endothelial growth factor (VEGF) were evaluated throughout the luteal phase and after PGF(2alpha)-induced luteolysis. Corpora lutea were collected from mares in the early luteal phase (days 3-4), mid-luteal phase ...
Sipahutar H, Sourdaine P, Moslemi S, Plainfossé B, Séralini GE.High levels of plasma estrogens constitute an endocrine peculiarity of the adult stallion. This is mostly due to testicular cytochrome p450 aromatase, the only irreversible enzyme responsible for the bioconversion of androgens into estrogens. To identify more precisely the testicular aromatase synthesis sites in the stallion, testes from nine horses (2-5 years) were obtained during winter or spring. Paraplast-embedded sections were processed using rabbit anti-equine aromatase, followed by biotinylated goat anti-rabbit antibodies, and amplified with a streptavidin-peroxidase complex. Immunoreac...
Soma LR, Uboh CE, Liu Y, Li X, Robinson MA, Boston RC, Colahan PT.This study investigated and compared the pharmacokinetics of intra-articular (IA) administration of dexamethasone sodium phosphate (DSP) into three equine joints, femoropatellar (IAS), radiocarpal (IAC), and metacarpophalangeal (IAF), and the intramuscular (IM), oral (PO) and intravenous (IV) administrations. No significant differences in the pharmacokinetic estimates between the three joints were observed with the exception of maximum concentration (Cmax ) and time to maximum concentration (Tmax ). Median (range) Cmax for the IAC, IAF, and IAS were 16.9 (14.6-35.4), 23.4 (13.5-73.0), and 46.9...
Abbara A, Ratnasabapathy R, Jayasena CN, Dhillo WS.The Kiss1 gene encodes a 145-amino acid pre-peptide, kisspeptin, which is cleaved into smaller peptides of 54, 14, 13, and 10 amino acids. This chapter reviews in detail the effects of kisspeptin on gonadotropin secretion in non-human mammals. Studies of kisspeptin's effects have included both acute and chronic administration regimens via a number of administration routes. Acute kisspeptin stimulates gonadotropin secretion in a wide range of species of non-human mammals, including rats, mice, hamsters, sheep, pigs, goats, cows, horses, and monkeys. In general, the stimulatory effect of kisspep...
McGowan CM.In laminitis occurring in the field, as opposed to laminitis occurring during hospitalization or severe illness, endocrinopathic laminitis is the predominant form of laminitis. Prevalent causes of endocrinopathic laminitis are ECS and EMS. Exclusion of inflammatory or weight bearing causes of laminitis and focussing on the identification and treatment of underlying endocrine conditions will improve laminitis management strategies.
de Ruijter-Villani M, Stout T.Implantation is a pivotal step in the establishment of mammalian pregnancy. Although implantation strategies vary between species, many aspects of conceptus-maternal signalling necessary to induce uterine receptivity to implantation are conserved. The temporal 'window' for the initiation of implantation is short and precisely controlled by endocrine, paracrine and autocrine factors. An invariable prerequisite for the development of uterine receptivity to implantation is continuous exposure of the endometrium to progesterone which, after a species-specific interval, downregulates progesterone r...
Malinowski K, Christensen RA, Hafs HD, Scanes CG.A survey with horses was conducted to determine whether plasma concentrations of triiodothyronine (T3), thyroxine (T4), insulin-like growth factor (IGF)-I and IGF binding proteins (IGFBP) change as horses grow, mature sexually, and age. Jugular blood was sampled from Standardbred fillies and mares at ages 0, 1, 7, and 14 d, at 1, 2, 4, 5, 6, and 9 mo, and at 5 to 8 and 16 to 22 yr (n = 5 to 18). In a second survey, we measured the same variables in eight breeds of horses with markedly different adult body sizes, from Miniatures to Friesians. Plasma T3, T4, and IGF-I were determined by radioimm...
Tait AD, Santikarn S, Allen WR.The 5,7-dienes, 3 beta-hydroxy-5,7-pregnadien-20-one and 3 beta-hydroxy-5,7-androstadien-17-one were extracted from fetal horse gonads and purified by solvent partition, thin-layer chromatography and high performance liquid chromatography. The isolated steroids were identified by comparison with the synthetic steroids using ultraviolet and mass spectroscopy and by gas chromatography-mass spectroscopy. The identification of these compounds as endogenous steroids, together with the data on their biosynthesis reported previously, support the proposal that in the fetal horse gonad there is a 5,7-d...
