Thyroid hormones in horses are biochemical substances produced by the thyroid gland, primarily including thyroxine (T4) and triiodothyronine (T3). These hormones are involved in regulating metabolism, growth, and development in equine species. They influence various physiological processes such as energy production, thermoregulation, and cardiovascular function. Abnormal levels of thyroid hormones can indicate thyroid dysfunction or other metabolic disorders in horses. This page compiles peer-reviewed research studies and scholarly articles that explore the synthesis, regulation, and clinical implications of thyroid hormones in equine health and disease.
Hilderbran AC, Breuhaus BA, Refsal KR.This study was performed to determine whether sick horses have thyroid hormone (TH) alterations similar to those observed in nonthyroidal illness syndrome in other species. Objective: Horses suffering from systemic diseases have decreased THs and inappropriately low thyroid-stimulating hormone (TSH). Methods: Seventy-one clinically normal horses; 380 hospitalized horses. Methods: Total thyroxine (TT4), free thyroxine by equilibrium dialysis (fT4D), total triiodothyronine (TT3), free triiodothyronine (fT3), and TSH were measured in normal and hospitalized horses. Disease severity was categorize...
Pirrone A, Panzani S, Govoni N, Castagnetti C, Veronesi MC.The hypothalamus-pituitary-thyroid axis has specific functions, mostly related to metabolic activities, cell differentiation, and development. To the authors' knowledge, there are no studies about thyroid hormone (TH) concentrations in foals affected by perinatal asphyxia syndrome (PAS). Hence, the aims of the study are (1) to evaluate plasma TH concentrations (T3 and T4) in healthy foals during the first 7 days of life; (2) to evaluate plasma TH concentration (T3 and T4) in critically ill foals affected by PAS during the first 7 days of hospitalization; and (3) to compare TH concentrations be...
Valencia NA, Thompson DL, Mitcham PB.Six insulin-sensitive and 6 insulin-insensitive mares were used in a replicated 3 by 3 Latin square design to determine the pituitary hormonal responses (compared with vehicle) to sulpiride and thyrotropin-releasing hormone (TRH), 2 compounds commonly used to diagnose pituitary pars intermedia dysfunction (PPID) in horses. Mares were classified as insulin sensitive or insensitive by their previous glucose responses to direct injection of human recombinant insulin. Treatment days were February 25, 2012, and March 10 and 24, 2012. Treatments were sulpiride (racemic mixture, 0.01 mg/kg BW), TRH (...
Brinkmann L, Gerken M, Riek A.Outdoor group housing is increasingly recognized as an appropriate housing system for domesticated horses. The objective of this study was therefore to investigate the effect of potential feed shortage in semi-natural horse keeping systems in winter on animal health and welfare. In 10 female Shetland ponies blood concentrations (NEFA, total protein (TP), total bilirubin (TB), beta-hydroxybutyrate (BHB) and thyroxine (T4)), body mass and the body condition score (BCS) were monitored for 7 months including a 4 months period of feed restriction in five of the 10 ponies. Restrictively fed animals ...
Mendoza FJ, Perez-Ecija RA, Toribio RE, Estepa JC.Reference intervals for thyroid hormones (TH) concentrations have not been previously established for donkeys, leading to potential misdiagnosis of thyroid disease. Objective: To determine the normal values of TH in healthy adult donkeys and compare them to TH values from healthy adult horses. Methods: Thirty-eight healthy Andalusian donkeys and 19 healthy Andalusian horses from 2 different farms were used. Donkeys were divided into 3 age groups: 11 years and into 2 gender groups. Serum concentrations of fT3, tT3, rT3, fT4 and tT4 were quantified by radioimmunoassay. All blood samples were col...
Squillacioti C, De Luca A, Alì S, Paino S, Liguori G, Mirabella N.Urocortin (UCN) is a 40-amino-acid peptide and a member of the corticotropin-releasing hormone (CRH) family, which includes CRH, urotensin I, sauvagine, UCN2 and UCN3. The biological actions of CRH family peptides are mediated via two types of G-protein-coupled receptors, namely CRH type 1 receptor (CRHR1) and CRH type 2 receptor (CRHR2). The biological effects of these peptides are mediated and modulated not only by CRH receptors but also via a highly conserved CRH-binding protein (CRHBP). Our aim was to investigate the expression of UCN, CRHR1, CRHR2 and CRHBP by immunohistochemistry, Wester...
Himler M, Hurcombe SD, Griffin A, Barsnick RJ, Rathgeber RA, MacGillivray KC, Toribio RE.Hypothalamic-pituitary-thyroid (HPT) axis dysfunction is associated with morbidity and mortality in critically ill people. To date, investigations of HPT axis in critically ill foals are limited. Objective: To document the occurrence of low thyroid hormone concentrations (presumptive nonthyroidal illness syndrome; NTIS) in critically ill newborn foals and investigate whether NTIS is associated with severity of disease and outcome. Objective: NTIS occurs frequently in foals with sepsis and is associated with sepsis score and outcome. Reverse T3 (rT3) concentrations will be increased in septic f...
Panzani S, Comin A, Galeati G, Romano G, Villani M, Faustini M, Veronesi MC.Thyroid hormones, insulin growth factor I (IGF-I) and non-esterified fatty acids (NEFA) represent important hormonal and metabolic factors associated with perinatal growth and maturation. Their action could be influenced by the type of parturition and the health status of the foal and therefore the aim of this work is to evaluate their plasma concentrations in newborn foals during the first 2 wks of life. Three groups of subjects were enrolled: 15 healthy foals born by spontaneous parturition, 24 healthy foals born by induced parturition and 26 pathologic foals. From each of the healthy foals,...
Cravana C, Medica P, Prestopino M, Fazio E, Ferlazzo A.Limited knowledge exists about the differentiated effects of competitive and noncompetitive showjumping on thyroid function and relationships with hypothalamic-hypophysis-corticoadrenal hormones. Objective: To obtain preliminary data about differentiated effects of competitive and noncompetitive showjumping on total and free iodothyronines, β-endorphin, ACTH and cortisol of horses. Methods: Five trained healthy jumper horses were studied during competitive and noncompetitive showjumping, performed in the same circuit design over 10 fences of 1.10 m. Hormone levels before, 5 and 30 min post ex...
Ferlazzo A, Medica P, Cravana C, Fazio E.Involvement of thyroid function on performance warrants further investigation as limited data exists on the effects of showjumping on the dynamics of total and free iodothyronines. Objective: To investigate the response of circulating total and free iodothyronines in horses to experimental showjumping sessions and compare with the effects normally induced by competition and determine if fence height has any effect. Methods: Using a randomised crossover study design 6 trained horses were studied during experimental showjumping sessions over 10 fences of different height: 1.00 m (Session 1), 1.1...
Leleu C, Haentjens F.The demands in the Standardbred trotters industry require young, still growing horses, to be trained well above light exercise level. During that period, the risk of occurrence of energy imbalance and maladaptation to training is high. In man, the lack of energy homeostasis is considered as the basic problem in the development of chronic fatigue. Objective: To find objective biomarkers of early maladaptation to training in young racehorses under field conditions. Methods: Sixty-five 2-year-old Standardbreds were followed during their first 3 months of training in 5 different training centres. ...
Breuhaus BA.Regulatory control of the thyroid gland in horses is similar to other species. Clinical signs of hypothyroidism in adult horses are minimal. Several drugs and physiologic and pathophysiological states can cause circulating thyroid hormone concentrations to be low without actual pathology of the thyroid gland. Thus, nonthyroidal factors must be ruled out before a diagnosis of hypothyroidism can be made. Thyroid hormone supplementation seems to be well tolerated, even in euthyroid horses. Neonatal foals have very high circulating thyroid hormone concentrations, and deficiencies result in signif...
Weisrock KU, Winkelsett S, Martin-Rosset W, Forssmann WG, Parvizi N, Coenen M, Vervuert I.Intermittent administration of parathyroid hormone (PTH) is an anabolic therapy for osteoporotic conditions in humans. This study evaluated the effects of equine PTH fragment (ePTH-1-37) administration on bone metabolism in 12 healthy horses. Six horses each were treated once daily for 120days with subcutaneous injections of 0.5μg/kg ePTH-1-37 or placebo. Blood was collected to determine ionized calcium (Ca(++)), total Ca (Ca(T)), inorganic phosphorus, serum equine osteocalcin (eOC), carboxy-terminal telopeptide of type I collagen (ICTP), bone-specific alkaline phosphatase, and carboxy-termin...
Medica P, Fazio E, Cravana C, Ferlazzo A.The aim of this study was to investigate thyroid hormone levels in horses stabled in two different locations on the island of Sicily. The study was carried out on a total of 72 clinically healthy Sanfratellano horses ranging in age from 5 to 9 years and weighing 585 ± 40 kg. The results showed higher thyroxine values (P < 0.02) in horses stabled in an endemic goitre area (group II) than those observed in horses in a non-endemic area (group I). Unexpectedly, the T(4)/T(3) and the fT(4)/fT(3) rations were both lower in group I than in group II. The percentages of fT(4) to T(4) and of fT(3) to T...
Davies S, Barber D, Crisman M, Tan R, Larson M, Daniel G.We characterized the scintigraphic and sonographic appearance of the thyroid gland in clinically normal horses to establish the value of these modalities for assessment of the thyroid gland in this species. Horses were divided into two age groups. One group consisted of eight horses between 3 and 10 years of age and the other of seven horses between 11 and 20 years of age. Total T4 concentrations were within the laboratory reference interval in all horses. Thyroid to salivary (T/S) ratio, percent dose uptake of pertechnetate (Na99mTcO4) and thyroid lobe volume were calculated. The echogenicity...
Muirhead TL, Wichtel JJ, Stryhn H, McClure JT.Serum selenium (Se), vitamin E, and resting thyroid hormone concentrations were measured in 201 horses in Prince Edward Island (PEI). Selenium concentrations were either marginal (0.0053 to 0.1200 ppm) or deficient (< 0.0053 ppm) in 79% of horses based on current reference ranges for Se in serum. Aged and young adult pleasure horses had a higher prevalence of inadequate Se concentrations compared to racehorses and broodmares (82% and 97% versus 45% and 72%, respectively). Overall, 13% of horses had inadequate (< 200 μg/dL) serum vitamin E concentrations; most of these were young pleasure hors...
Abraham G, Allersmeier M, Schusser GF, Ungemach FR.The aim of this study was to determine if topical application of dexamethasone affected the serum concentrations of thyroid hormones (triiodothyronine T(3) and thyroxine T(4)), glucose, triglycerides, total protein and insulin in normal horses. Ten horses were treated twice daily for 10 days with 50 g dexamethasone using an ointment formulation. Thyroid hormones and insulin were assayed using standard radioimmunoassay methods, while glucose, triglycerides and total protein were determined using a standard enzymatic method and the Biuret reaction, respectively. An increase in serum glucose and ...
Song Y, Massart C, Chico-Galdo V, Jin L, De Maertelaer V, Decoster C, Dumont JE, Van Sande J.In the literature, data obtained in signal transduction from various species thyroids and cells lines are often integrated in a common model. We investigate qualitatively and systematically, using the same protocol, the control by TSH of the two main functions of the thyrocytes, the synthesis and the secretion of thyroid hormones. In all species investigated, the TSH receptor activates both. In some species, including humans, rats and mice, the TSH receptor activates both the cAMP and phospholipase C-PIP2 cascades, in others (e.g. dog) it only stimulates the first. The cAMP pathway activates t...
Fazio E, Medica P, Cravana C, Giacoppo E, Ferlazzo A.In order to investigate the effects of short road transport stress on total and free iodothyronines, body weight (BW), rectal temperature and heart rate (HR) changes, 126 healthy stallions were studied in basal conditions, before and after transport. A total of 60 Thoroughbred and 66 crossbred stallions aged 4 to 15 years with previous travelling experience were transported by road in a commercial trailer for a period of about 3 to 4 h (distance under 300 km). Blood samples and functional variables were collected in each horse box, one week before loading and transport in basal conditions (con...
Rizzo A, Mutinati M, Spedicato M, Minoia G, Trisolini C, Punzi S, Roscino MT, Jirillo F, Sciorsci R.The beta-subunits of thyroid stimulating hormone (TSH) and human chorionic gonadotropin (hCG) share a high homology, just like the ectodomains of their receptors, do. As a consequence, hCG was shown to exert a thyrotropic action in humans and hamsters. This study aimed to investigate whether hCG, used to induce ovulation, displays a thyrotropic effect in the equine species too. Forty mares at estrus were divided in two groups; 20 were intravenously treated with sterile saline solution (NaCl 0.9%) (group A); 20 were intravenously treated with 4000 I.U. of hCG (group B). All the mares were artif...
Hurcombe SD, Toribio RE, Slovis NM, Saville WJ, Mudge MC, Macgillivray K, Frazer ML.Disorders of calcium regulation are frequently found in humans with critical illness, yet limited information exists in foals with similar conditions including septicemia. The purpose of this study was to determine whether disorders of calcium exist in septic foals, and to determine any association with survival. Objective: Blood concentrations of ionized calcium (Ca(2+)) and magnesium (Mg(2+)) will be lower in septic foals with concomitant increases in parathyroid hormone (PTH), calcitonin (CT), and parathyroid-related peptide (PTHrP) compared with healthy foals. The magnitude of these differ...
Breuhaus BA.This study was performed to determine whether anhidrotic horses have altered thyroid function compared with horses that sweat normally. Objective: Anhidrotic horses have normal thyroid function. Methods: Ten client-owned horses with clinical signs of anhidrosis were paired with 10 horses living in the same environment that had normal sweat production. Methods: Horses were diagnosed as having normal sweat production or being anhidrotic based on responses to intradermal injections of terbutaline and physiologic responses to lunging exercise. Control horses were selected from the same environment...
Rourke KM, Kohn CW, Levine AL, Rosol TJ, Toribio RE.Calcium has important physiological functions, and disorders of calcium homeostasis are frequent in horses. We have made important progress understanding equine calcium homeostasis; however, limited information on equine calcitonin (CT) is available, in part because of the lack of validated CT assays. To determine the CT response to high ionized calcium (Ca(2+)) concentrations in healthy horses, we induced hypercalcemia in 10 healthy horses using a calcium gluconate 23% solution (5mg/kg; 120 mL/500 kg horse) infused over 4 min. Four horses were infused with 120 mL of 0.9% NaCl and used as cont...
Fazio E, Medica P, Cravana C, Ferlazzo A.To evaluate whether the amount of experience of sport horses and the stress of transport affected their adrenocortical and thyroid responses, the plasma concentrations of total cortisol and total and free iodothyronine of 63 horses were studied before and after show jumping competitions. There were 14 trained inexperienced jumpers (group 1), 20 trained experienced jumpers (group 2), 10 trained inexperienced jumpers that had been transported just before the competition (group 3) and 19 trained experienced jumpers that had been transported just before the competition (group 4). The concentration...
Schwarz BC, Sallmutter T, Nell B.A 6-year-old 680-kg (1,496-lb) German Warmblood gelding was evaluated because of bilateral blepharospasm and head shaking. Results: Moderate blepharospasm was evident bilaterally, and both eyes had hyperemic and edematous conjunctivas and lusterless corneas. For each eye, the Schirmer tear test value was only 7 mm/min. The horse's nasal mucosa was dry. Abnormal behaviors included mild repetitive vertical movement of the head, snorting, and flehmen response (classic signs of head shaking). Touching the horse's nostrils and face revealed paresthesia and dysesthesia with slight nasolabial muscle ...
Calamari L, Ferrari A, Bertin G.This study was conducted to determine the effects of either dietary Se source or dose on the Se status of horses. Twenty-five mature horses were blocked by BW and randomly allocated to 1 of 5 dietary treatments that comprised the same basal diet that differed only in Se source or dose. Treatments were as follows: negative control (0.085 mg of Se/kg of DM), 3 different dietary concentrations of supplemental organic Se (Se yeast; 0.2, 0.3, and 0.4 mg of total Se/kg of DM), and positive control (0.3 mg of total Se/kg of DM) supplemented with Na selenite. Horses initially received the control diet...
Roser JF.It is well established in many mammalian species, including the horse that normal testicular function is dependent upon a functional hypothalamic-pituitary-testicular (HPT) axis, which involves classic feedback mechanisms. The major HPT hormones involved in the stallion are gonadotropin-releasing hormone (GnRH), luteinizing hormone (LH), follicle stimulating hormone (FSH), testosterone (T), estrogens (Es) and inhibin (INH). Although prolactin (PRL) fluctuates with season in the stallion and both PRL and thyroid hormone (TH) affect reproduction in other male species, their effects on stallion r...
Frank N, Buchanan BR, Elliott SB.To determine the effects of long-term oral levothyroxine sodium (L-T(4)) administration on serum thyroid hormone concentrations, thyroid gland function, clinicopathologic variables, and echocardiographic examination measurements in adult euthyroid horses. Methods: 6 healthy adult mares. Methods: Horses received L-T(4) (48 mg/d) orally for 48 weeks. Every 4 weeks, physical examinations were performed; blood samples were collected for CBC, plasma biochemical analyses, and assessments of serum total triiodothyronine (tT(3)) and thyroxine (tT(4)) concentrations. Plasma creatine kinase MB activity ...
Semevolos SA, Brower-Toland BD, Bent SJ, Nixon AJ.Early changes in parathyroid hormone-related peptide (PTH-rP) and Indian hedgehog (Ihh) expression were examined in equine articular osteochondrosis (OC) as a model of a naturally acquired dyschondroplasia. Cartilage was harvested from OC-affected femoropatellar or scapulohumeral joints from immature horses and normal control horses of similar age. PTH-rP expression levels were assessed by semi-quantitative PCR, in situ hybridization, and immunohistochemistry. Ihh protein expression levels were assessed by immunohistochemistry. Elevated PTH-rP protein and mRNA expression were identified in the...
Fuerst A, Derungs S, von Rechenberg B, Auer JA, Schense J, Watson J.To describe the treatment of a subchondral bone cyst in the proximal phalanx with parathyroid hormone peptide-enriched fibrin hydrogel in a warmblood filly. The cyst was localized with computer-assisted orthopaedic surgery, then curetted and finally filled with parathyroid hormone fragment peptide 1-34 (PTH(1-34)) covalently attached to a fibrin hydrogel. The cyst healed quickly without any complications. This result supports the hypothesis that PTH(1-34) delivered locally in a fibrin hydrogel may improve the postoperative prognosis of surgical management of subchondral bone cysts in horses. S...
Dalefield RR, Palmer DN.Thyroid tumours have been described as "moderately common" in horses, but diseases associated with them are rare and the actual incidence has not been reported. A survey of thyroids from 29 horses aged 12 to 32 years revealed gross lesions in 11 animals, all older than 17. Most lesions were microfollicular adenomas. There was no evidence that the horses suffered from long-standing iodine deficiency or diffuse hyperplasia. Adenomas were more common than hyperplastic nodules and it is unlikely that the former arose from the latter. One thyroid adenocarcinoma was discovered. Progression from thyr...
Lopez-Rodriguez MF, Cymbaluk NF, Epp T, Laarveld B, Thrasher M, Card CE.Iodine, thyroxine (T4) and triiodothyronine (T3) are required for normal fetal growth, maturation, and neonatal survival. There is a lack of robust information on iodine levels found in colostrum, milk, and serum of mares and foals after a healthy pregnancy. Our objective was to characterize colostrum, milk, and serum iodine levels in healthy postpartum mares and foals (n = 10) and explore relationships with thyroid hormone concentrations. Colostrum, milk, and jugular blood samples from draft breed mares and foals with an estimated average iodine daily intake of 39 mg per mare during pregnan...
Irvine CH.Hypothyroidism in the foal occurs as two entities because of the separate actions of thyroid hormones in regulation of metabolic rate and in cell differentiation. The hypometabolic state which results in inadequate thermogenesis and lethargy, occurs concurrently with a period when thyroid hormone secretion is inadequate. Also the severity of the concurrent symptoms is related to the degree of hormone inadequacy as measured by plasma concentrations of free T4 and T3. By contrast, the developmental lesions caused by hypothyroidism are often observed during periods when plasma thyroid hormone con...
Tangyuenyong S, Sato F, Nambo Y, Murase H, Endo Y, Tanaka T, Nagaoka K, Watanabe G.This study aimed to compare body growth, metabolic, and reproductive hormonal changes in trained Thoroughbred yearling horses under different climate conditions with and without light supplementation (LS). Thoroughbred yearlings raised at research centers of the Japan Racing Association in Hokkaido (north) or Miyazaki (south) were divided into control and LS groups. In the LS groups, 44 colts and 47 fillies from Hokkaido and 11 colts and 11 fillies from Miyazaki were exposed to LS with an extended photoperiod of 14.5 hr of daylight and 9.5 hr of darkness. One week before and once a month after...
Silver M, Fowden AL, Knox J, Ousey J, Cash R, Rossdale PD.Pre- and post partum changes in plasma T3 have been examined in relation to plasma cortisol in 23 newborn foals (12 full term, 6 premature and 5 'twilight'), and in 5 fetuses catheterized in late gestation. Blood samples were collected daily from the fetuses and from the neonates at 30-min intervals for 2 h after birth; the plasma was assayed for T3 and cortisol by standard radioimmunoassay methods. In the full-term foals, plasma cortisol and T3 concentrations were high at birth (67.4 +/- 6.1 and 4.3 +/- 0.3 ng/ml respectively) and rose to a maximum during the following 2-h period to 141.0 +/-...
González O, González E, Sánchez C, Pinto J, González I, Enríquez O, Martínez R, Filgueira G, White A.The effects of exercise stress on erythrocyte beta-adrenergic receptor characteristics and plasma concentrations of adrenaline, noradrenaline and thyroid hormones were studied in Thoroughbred racehorses during rest and after exercise. Five minutes after a maximal speed race of 1200 +/- 200 m (mean +/- s.d.), both plasma adrenaline and noradrenaline concentrations increased with respect to basal values (from 2.48 +/- 0.15 to 3.83 +/- 0.27 and from 2.13 +/- 0.11 to 3.53 +/- 0.27 nmol/l respectively). The increment of adrenaline was greater in high performance (HP) as compared to low performance ...
Breuhaus BA.This study was performed to compare thyroid function of premature foals to term foals. Objective: Premature foals are more markedly hypothyroxinemic than expected for their severity of illness alone. Methods: Twenty clinically normal term foals; 28 sick, hospitalized term foals; 24 sick, hospitalized premature foals. Methods: Thyroid hormones (TH) and thyrotropin (TSH) were measured, both at rest and in response to thyrotropin-releasing hormone (TRH), in the 3 groups of foals. Clinical and clinicopathologic data were recorded. Results: Normal foals had high TH at birth, which decreased over th...
Ferlazzo A, Cravana C, Fazio E, Medica P.In order to acquire a pattern of thyroid involvement in welfare maintenance in Ruminants and Equines, this review summarizes data concerning the reference values of total and free iodothyronines and their modifications in physiological conditions and in different management conditions (pregnancy, lactation, weaning, growth, isolation, restraint, shearing, confinement and transportation). Thyroidal and extrathyroidal tissues efficiently respond to management practices, giving a differentiated contribution to circulating iodothyronine changes. The hormonal response could be mainly attributed to ...
Panzani S, Comin A, Galeati G, Romano G, Villani M, Faustini M, Veronesi MC.Thyroid hormones, insulin growth factor I (IGF-I) and non-esterified fatty acids (NEFA) represent important hormonal and metabolic factors associated with perinatal growth and maturation. Their action could be influenced by the type of parturition and the health status of the foal and therefore the aim of this work is to evaluate their plasma concentrations in newborn foals during the first 2 wks of life. Three groups of subjects were enrolled: 15 healthy foals born by spontaneous parturition, 24 healthy foals born by induced parturition and 26 pathologic foals. From each of the healthy foals,...
Fradinho MJ, Mateus L, Bernardes N, Bessa RJB, Caldeira RM, Ferreira-Dias G.Development of a healthy musculoskeletal system is of high concern for horse breeders and users. A longitudinal field study was performed in order to: (i) evaluate growth patterns and long-term changes on bone quality, bone metabolism, growth factors and metabolic variables in the Lusitano horse; and (ii) retrospectively assess whether these changes were related with radiographic findings regarding osteochondrosis-like lesions (OC) at the onset of training. Thirty-four Lusitano foals born and raised at four stud-farms, were periodically weighed (BW), and measured (withers height-WH) from birth...
Vervuert I, Stanik K, Coenen M.Increasing levels of dietary calcium (Ca) and phosphorous (P) might have a negative impact on parathyroid hormone (PTH) response and result in a more pronounced hypocalcaemia during high-speed exercise in horses. Methods: In successive order, five trained horses were fed 33 g Ca and 19 g P (approximately 100% NRC, adequate intake), 64 g Ca and 38 g P (moderately high intake) or 96 g Ca and 56 g P (high intake). Each horse was adapted to each diet over a 21 day period before undergoing a standardised exercise test (SET) on a treadmill. The SET comprised 5 steps (each step 4 min duration, 3% inc...
Beech J, Garcia M.Cortisol, triiodothyronine (T3), thyroxine (T4), insulin, and glucose responses to thyrotropin-releasing hormone (TRH) were evaluated in 12 healthy, mature horses and in 7 horses and 4 ponies with clinical signs of pituitary adenoma (PA). Within 1 hour after TRH administration, the increase in T3 and T4 was similar in healthy horses and animals with PA. Plasma cortisol in the group with PA increased (P less than 0.05) within 0.25 hours after TRH administration, and remained increased for 1.5 hours. In the control group, a significant increase in plasma cortisol concentrations did not develop a...
Glade MJ, Gupta S, Reimers TJ.Growth-related skeletal diseases in young horses have been associated with high planes of nutrition, although the mechanisms underlying such an association have not been determined. It is likely that nutrition-induced effects on growth rate or growth quality involve the endocrine system. Hormonal and metabolic responses to the ingestion of meals containing either 80% (diet A) or 160% (diet B) of National Research Council energy and protein recommendations were examined in eight Thoroughbred weanling horses after 3 wk of dietary adaptation. After 24 h fasts, prefeeding serum concentrations of t...
Sommardahl CS, Frank N, Elliott SB, Webb LL, Refsal KR, Denhart JW, Thompson DL.To determine the effects of levothyroxine sodium (L-T4) on serum concentrations of thyroid gland hormones and responses to injections of thyrotropin-releasing hormone (TRH) in euthyroid horses. Methods: 12 healthy adult mares. Methods: 8 horses received an incrementally increasing dosage of L-T4 (24, 48, 72, or 96 mg of L-T4/d) for weeks 1 to 8. Each dose was provided for 2 weeks. Four additional horses remained untreated. Serum concentrations of total triiodothyronine (tT3), total thyroxine (tT4), free T3 (fT3), free T4 (fT4), and thyroid-stimulating hormone (TSH) were measured in samples obt...
Kuwamura M, Shirota A, Yamate J, Kotani T, Ohashi F, Sakuma S.A thyroid gland tumor, showing unusual histology, was identified in a 13-year-old male Andalusian horse. Microscopically, the tumor consisted of neoplastic proliferation of C-cell (parafollicular cell) with cytoplasmic fine granules, containing diffusely distributed, variously sized colloid-containing follicles. Immunohistochemically, the neoplastic C-cell were positive for calcitonin and follicleforming epithelial cells showed a positive reaction for thyroglobulin. Ultrastructurally, membrane-bound secretory granules up to 250 nm in diameter were found in the cytoplasm of the parafollicular c...
Fazio E, Medica P, Trifiletti C, Ferlazzo A.The objective of this study was to compare in detail the total and free iodothyronines' pattern of mares from the first ovulation of the year over an extended period of 12 weeks. A total of 20 mares were used in the study. The mares were classified into two groups: mares mated at the ovulation (n = 10) used as observational group and mares unmated at the ovulation (n = 10) used as control group. Serum total and free triiodothyronine (T3, fT3) and thyroxine (T4, fT4) levels were measured in baseline conditions at the first ovulation of year and once a week until 12 weeks later. For the experi...
Rourke KM, Kohn CW, Levine AL, Rosol TJ, Toribio RE.Calcium has important physiological functions, and disorders of calcium homeostasis are frequent in horses. We have made important progress understanding equine calcium homeostasis; however, limited information on equine calcitonin (CT) is available, in part because of the lack of validated CT assays. To determine the CT response to high ionized calcium (Ca(2+)) concentrations in healthy horses, we induced hypercalcemia in 10 healthy horses using a calcium gluconate 23% solution (5mg/kg; 120 mL/500 kg horse) infused over 4 min. Four horses were infused with 120 mL of 0.9% NaCl and used as cont...
Abraham G, Allersmeier M, Schusser GF, Ungemach FR.The aim of this study was to determine if topical application of dexamethasone affected the serum concentrations of thyroid hormones (triiodothyronine T(3) and thyroxine T(4)), glucose, triglycerides, total protein and insulin in normal horses. Ten horses were treated twice daily for 10 days with 50 g dexamethasone using an ointment formulation. Thyroid hormones and insulin were assayed using standard radioimmunoassay methods, while glucose, triglycerides and total protein were determined using a standard enzymatic method and the Biuret reaction, respectively. An increase in serum glucose and ...
Aguilera-Tejero E, Estepa JC, López I, Bas S, Garfia B, Rodríguez M.To evaluate changes in plasma ionized calcium (Ca2+) and parathyroid hormone (PTH) concentrations in horses competing in endurance rides. Methods: Longitudinal clinical study. Methods: 28 horses. Methods: Venous blood samples were obtained from horses before and after racing 80 km. Plasma pH and concentrations of Ca2+, PTH, inorganic phosphorus, albumin, lactate, and magnesium were measured. Results: Overall, a significant decrease in mean (+/- SD) plasma Ca2+ concentration (from 6.44 +/- 0.42 to 5.64 +/- 0.42 mg/dl) and a significant increase in plasma PTH concentration (from 49.9 +/- 30.1 to...
Kam YN, McKenzie K, Coyle M, Bertin FR.Pituitary pars intermedia dysfunction (PPID) is a common endocrinopathy of horses diagnosed with a thyrotropin-releasing hormone (TRH) stimulation test. Objective: Describe the repeatability of TRH stimulation in horses with and without PPID in winter and autumn. Methods: Twenty adult horses; 6 controls and 6 with PPID tested in autumn, 8 controls and 6 with PPID tested in winter with 3 controls and 3 with PPID tested in both seasons. Methods: Thyrotropin-releasing hormone stimulation was performed on 2 consecutive occasions, 1 week before and 1 week after the winter solstice and the autumn ...
Breuhaus BA, Refsal KR, Beyerlein SL.The purpose of the study reported here was to validate measurement of free thyroxine (fT4) concentration in equine serum by equilibrium dialysis (fT4D), and to compare values with fT4 concentration measured directly and with total T4 (TT4) concentration. The fT4D, fT4, and TT4 concentrations were measured over a range of values in euthyroid horses and horses made hypothyroid by administration of propylthiouracil (PTU). Concentrations of fT4D (<1.8-83 pmol/L) were consistently higher than those of fT4 (<1-40 pmol/L). There was a significant (P < .001) regression of fT4D on fT4 in 503 s...
Barton MH, Sharma P, LeRoy BE, Howerth EW.A 13-year-old gelding was examined because of weight loss, hyperglobulinemia, and hypercalcemia. Possible causes of hypercalcemia that were considered included renal failure, primary hyperparathyroidism, vitamin D toxicosis, and malignancy. There was no history of vitamin D ingestion, and serum creatinine and parathyroid hormone concentrations were normal, making renal failure and primary hyperparathyroidism unlikely. The hypercalcemia was suspected to be a result of malignancy, but thorough testing did not reveal any neoplastic disease. Eight months later, serum parathyroid hormone-related pr...
Aguilera-Tejero E, Estepa JC, López I, Bas S, Rodríguez M.Secondary hyperparathyroidism is a well known complication of renal failure in man (Llach 1995), carnivores (Nagode and Chew1992) and rodents (Bover et al.1994). In these species, renal disease results in increased synthesis and secretion of parathyroid hormone (PTH) and parathyroid gland hyperplasia. There are 3 main factors involved in the development ofsecondary hyperparathyroidism: a) phosphate (P) retention, dueto reduced glomerular filtration rate; b) decrease in calcitriol(CTR) production, as a consequence of renal mass loss; and c...
