Insulin is a hormone produced by the pancreas that plays a pivotal role in regulating glucose metabolism in horses. It facilitates the uptake of glucose by cells, thus maintaining blood sugar levels within a normal range. Insulin's function is integral to energy balance and metabolic processes in equines. Disruptions in insulin regulation can lead to metabolic disorders such as Equine Metabolic Syndrome (EMS), characterized by insulin resistance and associated with obesity and laminitis. This page aggregates peer-reviewed research studies and scholarly articles that explore the physiological role, regulatory mechanisms, and clinical implications of insulin in equine health and disease management.
Lewis SL, Holl HM, Streeter C, Posbergh C, Schanbacher BJ, Place NJ, Mallicote MF, Long MT, Brooks SA.Equine obesity can cause life-threatening secondary chronic conditions, similar to those in humans and other animal species. Equine metabolic syndrome (EMS), primarily characterized by hyperinsulinemia, is often present in obese horses and ponies. Due to clinical similarities to conditions such as pituitary pars intermedia dysfunction (formerly equine Cushing's disease), conclusive diagnosis of EMS often proves challenging. Aside from changes in diet and exercise, few targeted treatments are available for EMS, emphasizing the need for early identification of at-risk individuals to enable imple...
Baskerville CL, Bamford NJ, Harris PA, Bailey SR.Insulin-like growth factor-1 (IGF-1) plays several important physiological roles, and IGF-related pathways have been implicated in developmental osteochondral disease and endocrinopathic laminitis. This factor is also a downstream marker of growth hormone activity and its peptide mimetics. Unfortunately, previously used assays for measuring equine IGF-1 (radioimmunoassays and ELISAs) are no longer commercially available, and many of the kits on the market give poor results when used on horse samples. The aim of the present study was to compare three different ELISA assays (two human and one ho...
Lane HE, Burns TA, Hegedus OC, Watts MR, Weber PS, Woltman KA, Geor RJ, McCutcheon LJ, Eades SC, Mathes LE, Belknap JK.Insulin dysregulation, obesity, and exposure to high-nonstructural carbohydrate (NSC) forage are risk factors for equine metabolic syndrome-associated laminitis (EMSAL); high systemic insulin concentrations in EMSAL are proposed to induce cellular dysregulation in the digital lamellae through activation of the insulin-like growth factor-1 receptor. Objective: To use a dietary challenge model (DCM) and a euglycaemic-hyperinsulinaemic clamp (EHC) model to assess lamellar growth factor-related signalling. Methods: Lamellar phospho (P)-protein concentrations of signalling proteins important in gro...
Elzinga SE, Rohleder B, Schanbacher B, McQuerry K, Barker VD, Adams AA.Extracts derived from the leaves of the stevia plant (stevioside) are commonly used as sweeteners for humans and horses. Stevioside appears to be safe for human consumption, including for individuals with insulin dysregulation. In the horse, the safety or metabolic effects of stevioside on normal animals or on those with metabolic dysfunction are unknown. Furthermore, the inflammatory response to a glycemic challenge or to stevioside in horses is not well defined. Therefore, the objective of this study was to measure the effects of stevioside and a glycemic challenge on insulin, glucose, and i...
Carslake HB, Pinchbeck GL, McGowan CM.Many diagnostic tests for insulin dysregulation use reference intervals established with an insulin radioimmunoassay (RIA) that is no longer available. A chemiluminescent immunoassay (CLIA) is commonly used for the measurement of serum insulin concentration in clinical practice but requires further validation, especially at clinically relevant reference intervals. Objective: To evaluate the CLIA for measurement of equine insulin and compare it to the previously validated, but now unavailable RIA. Methods: Equine serum samples (n = 78) from clinical and experimental studies. Methods: In this ex...
Smith S, Marr CM, Dunnett C, Menzies-Gow NJ.Birthweight of Thoroughbred foals has increased in recent years. It is unknown whether this is associated with increased broodmare obesity or endocrine dysfunction. Objective: To determine insulin, leptin and triglyceride concentrations in Thoroughbred mares throughout gestation and investigate their association with obesity and foal birthweight. Methods: Cohort study. Methods: A total of 66 mares were included from 40 days post-breeding. Body condition score (BCS), weight and blood samples were obtained every 60 days throughout gestation. Serum/plasma insulin, leptin and triglyceride concentr...
Valenzuela OA, Jellyman JK, Allen VL, Holdstock NB, Forhead AJ, Fowden AL.In several species, adult metabolic phenotype is influenced by the intrauterine environment, often in a sex-linked manner. In horses, there is also a window of susceptibility to programming immediately after birth but whether adult glucose-insulin dynamics are altered by neonatal conditions remains unknown. Thus, this study investigated the effects of birth weight, sex and neonatal glucocorticoid overexposure on glucose-insulin dynamics of young adult horses. For the first 5 days after birth, term foals were treated with saline as a control or ACTH to raise cortisol levels to those of stressed...
Marycz K, Kornicka K, Grzesiak J, Śmieszek A, Szłapka J.Equine metabolic syndrome (EMS) is mainly characterized by insulin resistance, obesity, and local or systemic inflammation. That unfriendly environment of adipose tissue has huge impact on stem cells population (ASC) residing within. In the present study, using molecular biology techniques and multiple imaging techniques (SEM, FIB-SEM, and confocal microscopy), we evaluated the impact of EMS on ASC viability and chondrogenic differentiation. Moreover, we visualized the mitochondrial network and dynamics in ASC and ASC during control and chondrogenic conditions. In control conditions, ASC were ...
Van Dijk P, Lankveld D, Rijkenhuizen A, Jonker FH.To assess the hormonal, metabolic and physiological effects of laparascopic surgery performed under a sedative analgesic combination of detomidine and buprenorphine in standing horses. Methods: Prospective study. Methods: Eight healthy adult Dutch Warmblood horses and five healthy adult ponies undergoing laparoscopy were studied. Five healthy adult horses not undergoing laparoscopy were used as a control group. Methods: The sedative effect of an initial detomidine and buprenorphine injection was maintained using a continuous infusion of detomidine alone. The heart and respiratory rate, arteria...
Van Dijk P, Lankveld D, Rijkenhuizen A, Jonker FH.To assess the hormonal, metabolic and physiological effects of laparascopic surgery performed under a sedative analgesic combination of detomidine and buprenorphine in standing horses. Methods: Prospective study. Methods: Eight healthy adult Dutch Warmblood horses and five healthy adult ponies undergoing laparoscopy were studied. Five healthy adult horses not undergoing laparoscopy were used as a control group. Methods: The sedative effect of an initial detomidine and buprenorphine injection was maintained using a continuous infusion of detomidine alone. The heart and respiratory rate, arteria...
Brøkner C, Austbø D, Næsset JA, Blache D, Knudsen KE, Hansen HH, Tauson AH.Dietary sugar and starch affect plasma glucose and insulin concentrations. Little information is available about the effect of dietary fibre on plasma glucose and insulin concentration. It is hypothesized that different dietary fibre compositions will alter post-prandial glycaemic- and insulinemic index of test meals. The objective was to measure postprandial glucose and insulin concentrations in horses fed meals of different fibre compositions. Methods: Blood was drawn via jugular vein puncture and the glycaemic and insulinemic index were calculated. Results: The meal effect on glycaemic and ...
Nostell KE, Lindåse SS, Bröjer JT.Insulin resistance (IR) in humans is related to hypertension and impaired vasodilation. Insulin administration has been shown to lower blood pressure both in insulin resistant as well as in insulin sensitive individuals. The aim of the study was to investigate the association between insulin sensitivity and alterations in blood pressure in healthy horses before and after a euglycemic-hyperinsulinemic clamp (EHC). A 3-h EHC was performed in 13 healthy horses (11 mares, 2 geldings). Blood samples for measurement of plasma glucose and insulin were collected before the start of the EHC, every 10 ...
Lindåse S, Nostell K, Bröjer J.An oral sugar test (OST) using Karo® Light Corn Syrup has been developed in the USA as a field test for the assessment of insulin dysregulation in horses but the syrup is not available in Scandinavian grocery stores. The aim of the study was to compare the results of a modified OST between horses with equine metabolic syndrome (EMS) and healthy horses using a Scandinavian commercially available glucose syrup (Dansukker glykossirap). In addition, the effect of breed and the repeatability of the test were evaluated. In the present study, clinically healthy horses (7 Shetland ponies, 8 Icelandic...
de Laat MA, Hampson BA, Sillence MN, Pollitt CC.Obesity in horses is increasing in prevalence and can be associated with insulin insensitivity and laminitis. Current treatment strategies for obesity include dietary restriction and exercise. However, whether exercise alone is effective for decreasing body fat is uncertain. Objective: Our hypothesis was that twice daily use of a dynamic feeding system for 3 months would induce sustained, low-intensity exercise thereby decreasing adiposity and improving insulin sensitivity (SI). Methods: Eight, university-owned, mixed-breed, adult ponies with body condition scores (BCS) ≥5/9 were used. Metho...
Warnken T, Huber K, Feige K.Exact analysis of equine insulin in blood samples is the key element for assessing insulin resistance or insulin dysregulation in horses. However, previous studies indicated marked differences in insulin concentrations obtained from sample analyses with different immunoassays. Most assays used in veterinary medicine are originally designed for use in human diagnostics and are based on antibodies directed against human insulin, although amino acid sequences between equine and human insulin differ. Species-specific assays are being used more frequently and seem to provide advantages compared to ...
Knowles EJ, Harris PA, Elliott J, Menzies-Gow NJ.It is recommended that the oral sugar test (OST) for insulin dysregulation (ID) be performed after an overnight fast, but fasting is impractical in ponies kept solely at pasture. There are few data on OST repeatability and reliability in ponies. Objective: To report 1) whether OST results obtained in the morning after an overnight fast or without fasting in the afternoon (FASTING/FED) can be used interchangeably, 2) time of highest insulin concentration T [insulin], repeatability and reliability of insulin response to the OST when FASTING or FED and 3) dichotomous agreement (ID/normal) within ...
Menzies-Gow NJ, Harris PA, Elliott J.Certain individuals appear to be predisposed to recurrent pasture-associated laminitis. Previous studies have predominantly investigated risk factors only after disease occurrence. Objective: To investigate risk factors for pasture-associated laminitis prior to disease occurrence. Methods: Prospective cohort study. Methods: Non-laminitic ponies aged ≥7 years were recruited. Body condition score (BCS), height, weight, crest height and thickness were measured and an overnight dexamethasone suppression test performed. Plasma or serum adiponectin, leptin, triglyceride, basal insulin, insulin pos...
Bertin FR, Taylor SD, Bianco AW, Sojka-Kritchevsky JE.Published descriptions of the oral sugar test (OST) and insulin response test (IRT) have been inconsistent when specifying the protocol for fasting horses before testing. The purpose of our study was to examine the effect of fasting duration on blood glucose concentration, blood insulin concentration, glucose/insulin ratio, OST, and IRT results in horses. Methods: Ten healthy adult horses. Methods: Both OST and IRT were performed on horses without fasting and after fasting for 3, 6, and 12 hours. Thus, 8 tests were performed per horse in a randomized order. Blood collected at the initial time ...
Banse HE, Holbrook TC, Frank N, McFarlane D.Local (skeletal muscle and adipose) and systemic inflammation are implicated in the development of obesity-associated insulin resistance in humans. In horses, obesity is neither strongly nor consistently associated with systemic inflammation. The role of skeletal muscle inflammation in the development of insulin dysregulation (insulin resistance or hyperinsulinemia) remains to be determined. We hypothesized that skeletal muscle inflammation is related to obesity-associated hyperinsulinemia in horses. Thirty-five light-breed horses with body condition scores (BCSs) of 3/9 to 9/9 were studied, i...
Restifo MM, Frank N, Hermida P, Sanchez-Londoño A.OBJECTIVE To assess effects of withholding feed on thyrotropin-releasing hormone (TRH) stimulation test results used in diagnosis of pituitary pars intermedia dysfunction in horses and determine effects of combined testing on results of the TRH stimulation test and the oral sugar test (OST) used in diagnosis of equine metabolic syndrome. ANIMALS 30 adult horses. PROCEDURES All horses underwent TRH stimulation tests under fed and nonfed conditions, an OST alone, and an OST combined with TRH stimulation testing. For TRH stimulation tests, plasma ACTH concentrations were measured before (baseline...
de Laat MA, Sillence MN.Insulin dysregulation can be difficult to diagnose from basal insulin and glucose concentrations, so a field-based oral glucose test (OGT) is preferred. However, the repeatability of this test has not been reported. Objective: To determine the repeatability of an in-feed OGT in ponies and examine some factors affecting the palatability of the test meal. Methods: A repeated measures, longitudinal study. Methods: An in-feed OGT was performed at 08.00 h on 3 consecutive occasions under controlled conditions in 8 mixed breed ponies. d-glucose (0.75 g/kg bwt) was dissolved in water and combined wit...
de Laat MA, van Haeften JJ, Sillence MN.Managing equine hyperinsulinemia is crucial for preventing laminitis, but our understanding of the mechanisms involved in insulin dysregulation in this species is incomplete. C-peptide is co-secreted with insulin but is resistant to hepatic metabolism and can be used to study insulin dysregulation. This study examined C-peptide secretion in serial blood samples collected after oral and i.v. dextrose (0.75 g/kg) administration to 9 ponies (BCS, 7.1 ± 0.5). The ponies were designated as hyperinsulinemic (HI) or normoinsulinemic (NI) responders before the study, using oral glucose tests and fast...
Dunbar LK, Mielnicki KA, Dembek KA, Toribio RE, Burns TA.Several tests have been evaluated in horses for quantifying insulin dysregulation to support a diagnosis of equine metabolic syndrome. Comparing the performance of these tests in the same horses will provide clarification of their accuracy in the diagnosis of equine insulin dysregulation. Objective: The aim of this study was to evaluate the agreement between basal serum insulin concentrations (BIC), the oral sugar test (OST), the combined glucose-insulin test (CGIT), and the frequently sampled insulin-modified intravenous glucose tolerance test (FSIGTT). Methods: Twelve healthy, light-breed ho...
Carslake H, Karikoski N, Pinchbeck G, McGowan C.Serum insulin concentration is commonly measured during investigation of suspected endocrinopathic disease in horses, but immediate analysis is frequently unavailable. The aim of this study was to examine the effect of storing samples at room temperature for 72 h as serum and as whole blood, compared to immediate separation and freezing. Samples from 14 horses were evaluated. Correlation was excellent for all comparisons (≥0.992). Bland-Altman plots revealed a negative bias (mean difference 2.16 µIU/mL) in samples stored as whole blood compared to serum, but this difference was not cons...
Lindåse SS, Nostell KE, Müller CE, Jensen-Waern M, Bröjer JT.To quantify insulin sensitivity and monitor glucose, insulin, and lipid concentrations in a group of moderately insulin-resistant horses during induction of obesity by use of a forage diet supplemented with fat and during subsequent turnout to pasture. ANIMALS 9 adult Standardbred mares (11 to 20 years old). Methods: Weight gain of horses was induced during 22 weeks by use of a forage diet supplemented with fat fed in gradually increasing amounts, followed by feeding of that fat-supplemented diet at 2.5 times the daily maintenance requirements. Horses were then turned out to pasture. Insulin s...
Martin-Gimenez T, de Blas I, Aguilera-Tejero E, Diez de Castro E, Aguirre-Pascasio CN.Equine metabolic syndrome (EMS) can be diagnosed by hormonal measurements; however, it would be important to find simpler measurements that allow easy identification of affected or at risk individuals. In horses, the dorsal neck region is one of the most frequent anatomical sites for fat deposition and neck obesity has been linked to EMS. The aim of this study was to evaluate the association of hormonal markers of obesity (leptin) and insulin resistance (insulin) with morphometric and ultrasonographic neck measurements in Andalusian horses. Plasma leptin and insulin concentrations were measure...
Valenzuela OA, Jellyman JK, Allen VL, Holdstock NB, Fowden AL.Synthetic glucocorticoids are used to treat inflammatory conditions in horses. In other pregnant animals, glucocorticoids are given to stimulate fetal maturation with long-term metabolic consequences for the offspring if given preterm. However, their metabolic effects during equine pregnancy remain unknown. Objective: Thus, this study investigated the metabolic effects of dexamethasone administration on pregnant pony mares and their foals after birth. Methods: Experimental study. Methods: A total of 3 doses of dexamethasone (200 μg/kg bwt i.m.) were given to 6 pony mares at 48 h intervals beg...
Bamford NJ, Potter SJ, Baskerville CL, Harris PA, Bailey SR.The relationships between diet, obesity and insulin dysregulation in equids require further investigation due to their association with laminitis. This study examined the effect of dietary glycaemic load and increased adiposity on insulin sensitivity and adipokine concentrations in different equine breeds. Equal numbers of Standardbred horses, mixed-breed ponies and Andalusian horses were provided with ad libitum hay plus either cereal-rich (CHO; n = 12), fat-rich (FAT; n = 12) or control (CON; n = 9) meals over 20 weeks. The isocaloric CHO and FAT diets were fed to induce obesity ...
Hart KA, Wochele DM, Norton NA, McFarlane D, Wooldridge AA, Frank N.Increased free cortisol fraction is associated with insulin dysregulation (ID) in people with Metabolic Syndrome and Cushing's Disease. Free cortisol has not been investigated in equine endocrine disorders. Objective: (1) In healthy horses, sex, age, body condition score (BCS), and season impact free cortisol; (2) free cortisol is increased in horses with Pituitary Pars Intermedia Dysfunction (PPID) or Equine Metabolic Syndrome (EMS). Methods: Fifty-seven healthy horses; 40 horses and ponies with PPID (n = 20) or EMS (n = 20). Methods: Prospective study. Serum collected seasonally from healthy...
Sandow C, Fugler LA, Leise B, Riggs L, Monroe WT, Totaro N, Belknap J, Eades S.Laminitis has a considerable impact on the equine industry. Endocrinopathic laminitis is the most common form and affected horses often have hyperinsulinaemia due to an underlying metabolic disorder. Objective: The aim of this study was to determine if insulin weakens the structural integrity of digital lamellae and to develop an ex vivo model for the study of hyperinsulinaemia-induced lamellar failure. Methods: Ex vivo experiment. Methods: Biomechanical testing was used to assess the structural integrity of lamellar explants exposed to either medium alone (control) or medium supplemented with...
Tranquilli WJ, Thurmon JC, Neff-Davis CA, Davis LE, Benson GJ, Hoffman W, Lock TF.Plasma glucose and serum insulin concentrations in Thoroughbreds administered xylazine hydrochloride (1.1 mg/kg; IV) and ketamine hydrochloride (2.2 mg/kg; IV) at dosages sufficient to induce short periods of recumbency and anesthesia were measured. Samples of blood were collected from 6 adult horses before, during, and after the anesthetic period. Plasma glucose (mg/dl) was significantly increased above control (-30 minute concentration) from 15 to 150 minutes after xylazine administration with the peak value occurring at 30 minutes. Serum insulin (microU/ml) was significantly decreased from ...
Waitt LH, Cebra CK.To characterize signalment, clinical signs of disease, and clinical response to insulin in equids with hypertriglyceridemia. Methods: Retrospective case series. Methods: 20 horses, 17 ponies, and 7 donkeys with hypertriglyceridemia. Methods: For analysis of medical record data, horses, donkeys, and ponies with multiple serum or plasma triglycerides measurements were separated into groups. Hypertriglyceridemic equids that were (HT-I; n = 14) or were not (HT-N; 10) treated with insulin consisted of equids with an initial triglycerides concentration > 44 mg/dL but < 500 mg/dL. Equids with an init...
Duehlmeier R, Hacker A, Widdel-Bigdely A, von Engelhardt W, Sallmann HP.Glucose homeostasis depends on insulin-regulated glucose uptake in the skeletal muscles and fat tissues via glucose transporter (GLUT) 4 translocation into cellular plasma membranes. The present study sought to elucidate GLUT4 expression, GLUT1 and GLUT4 translocation and glucose uptake in the skeletal muscles of Shetland ponies. Semitendinosus muscle explants were removed by open muscle biopsy from six Shetland pony geldings under general anaesthesia. The expression of GLUT4 was analysed by measuring muscle crude membrane (CM) GLUT4 protein contents. To determine the insulin-stimulated GLUT t...
Gehlen H, Twickel S, Stöckle S, Weber C, Bartmann CP.Pituitary pars intermedia dysfunction is the most prevalent endocrine disease in horses. Although donkeys and mules may also be affected, only a few data have been published. Reference values for diagnostic parameters, such as adrenocorticotropic hormone (ACTH), are especially scarce or even lacking. Therefore, in the present study, available data from the literature have been verified and completed to facilitate a reliable diagnosis. Clinical inspections and haematological and biochemical examinations were carried out four times in a three-month interval (February to November) in 44 donkeys a...
Mogg TD, Palmer JE.The medical records of 23 American Miniature Horses with hyperlipidemia, hyperlipemia, or hepatic lipidosis were reviewed. The most common clinical signs were anorexia and lethargy. The mean duration of clinical signs was 2.4 days. A primary disease was identified in 19 cases. Enterocolitis was the most common primary disease (n = 10). Intentional feed restriction, as part of treatment for colic, resulted in hyperlipemia in 2 horses and hyperlipidemia in 1. Four horses had primary hyperlipemia, 3 of which had signs of hepatoencephalopathy secondary to hepatic lipidosis. Dextrose, heparin, and ...
Ousey JC, Fowden AL, Wilsher S, Allen WR.Chronic and acute alterations in maternal nutrient intake during pregnancy alter pancreatic and hypothalamo-pituitary-adrenal (HPA) axis function in the offspring, before and after birth. Little is known about these effects. Objective: To determine whether maternal nutrient restriction caused by natural infection with Streptococcus equi altered endocrine function in neonatal foals born from mares fed a maintenance or high plane of nutrition throughout pregnancy. Methods: Ten primiparous mares received either a diet to maintain moderate body condition score (Moderate, n = 5) or a near ad libitu...
Nielsen BD, Vick MM, Dennis PM.Iron overload disorder afflicts captive rhinoceros but has not been documented in the wild. The specific cause for the disorder has not been identified but is likely associated with diet and management. Compared with wild counterparts, captive rhinoceros eat diets containing more iron, have greater fat stores, and exercise less. It has been suggested that the problem may be linked to development of insulin resistance in the captive population. Given that controlled experiments with sufficient numbers of rhinoceros are logistically not possible, an equine model was used to look for a relationsh...
Jensen RB, Rockhold LL, Tauson AH.The main objectives of this study were to evaluate the accuracy of different body weight formulas for estimating body weight of Icelandic and Warmblood horses, as well as to assess the associations between the variables cresty neck score, body condition score, and plasma concentrations of leptin, insulin and cortisol. A total of 81 adult (≥ 4 years of age) horses (43 Icelandic and 38 Warmblood horses) was included in this study. The following morphological measurements were collected by two examiners simultaneously; body weight; height at withers; neck length; 0.5 neck length; neck circum...
Ho EN, Wan TS, Wong AS, Lam KK, Stewart BD.Insulin administration can increase muscle glycogen by utilising hyperinsulinaemic clamps prior to sports events or during the recovery phases, and increase muscle size by its chalonic action to inhibit protein breakdown. In order to control insulin abuse in equine sports, a method to detect effectively the use of insulins in horses would be required. Besides the readily available human insulin and its synthetic analogues, structurally similar insulins from other species can also be used as doping agents. This study describes a method for the simultaneous detection of bovine, porcine and human...
Salazar-Ortiz J, Monget P, Guillaume D.Feed intake affects the GH-IGF system and may be a key factor in determining the ovarian follicular growth rate. In fat mares, the plasma IGF-1 concentration is high with low GH and a quick follicular growth rate, in contrast to values observed in thin mares. Nothing is known regarding the long-term effects of differential feed intake on the IGF system. The objective of this experiment was to quantify IGFs, IGFBPs, GH, glucose, insulin, gonadotropin and progesterone (P4) in blood and in preovulatory follicular fluid (FF) in relation to feeding levels in mares. Methods: Three years prior to the...
Macon EL, Harris P, Barker VD, Adams AA.Seasonal effects on the oral sugar test (OST), used to monitor insulin dysregulation (ID) status to help reduce laminitis risk, are poorly understood in the ID horse. Resting, (basal) insulin (T0) and 60-minute (T60) OST (0.15 mL/Kg BW Karo Light Corn Syrup) insulin responses were evaluated, once per each season over 2 years, in ID (n = 11 14.9 ± 4.3 years; mean ± SD) and non-insulin dysregulated (NID: n = 11 16.4 ± 5.3 years; mean ± SD) horses housed on the same farm. Seasonal morphometric measurements were collected: bodyweight (BW), body-condition scores (BCS), and cresty neck score...
Sticker LS, Thompson DL, Bunting LD, Fernandez JM, DePew CL.Sixteen light horse mares (8 to 9 yr of age; 457 to 579 kg BW) were fed Bermudagrass hay and a corn/cottonseed hull-based supplement formulated to contain either 100% (control) or 50% (restricted) of the protein and(or) energy requirements for maintenance in a 2 x 2 factorial arrangement of treatments. Daily measurements of intake, BW, and plasma hormones and metabolites were made for 33 d. Plasma glucose, insulin, NEFA, and urea N were measured in hourly samples drawn on d 27, and parallel with an i.v. glucose tolerance test (IVGTT) and epinephrine challenge on d 29. Energy restriction increa...
van de Lest CH, van den Hoogen BM, van Weeren PR.The object of this study was to determine whether changes in the synovial fluid (SF) induced by in vivo loading can alter the metabolic activity of chondrocytes in vitro, and, if so, whether insulin-like growth factor-I (IGF-I) is responsible for this effect. Therefore, SF was collected from ponies after a period of box rest and after they had been exercised for a week. Normal, unloaded articular cartilage explants were cultured in 20% solutions of these SFs for 4 days and chondrocyte bioactivity was determined by glycosaminoglycan (GAG) turnover (i.e., the incorporation of 35SO4 into GAG and ...
Kritchevsky JE, Muir GS, Leschke DHZ, Hodgson JK, Hess EK, Bertin FR.In metabolically stable horses, alpha-2-agonists suppress insulin secretion with transient hyperglycemia and rebound hyperinsulinemia. In horses with insulin dysregulation (ID), the effect of alpha-2-agonists has not been investigated; however, both the alpha-2-agonist-induced suppression of insulin secretion and rebound hyperinsulinemia could have clinical relevance. Objective: In horses with ID, alpha-2-agonists will alter insulin and glucose dynamics. Methods: Seven horses with ID and 7 control horses. Methods: In this randomized crossover study, xylazine hydrochloride (1.1 mg/kg) or detomi...
Ho EN, Wan TS, Wong AS, Lam KK, Stewart BD.Insulin and its analogues have been banned in both human and equine sports owing to their potential for misuse. Insulin administration can increase muscle glycogen by utilising hyperinsulinaemic clamps prior to sports events or during the recovery phases, and increase muscle size by its chalonic action to inhibit protein breakdown. In order to control insulin abuse in equine sports, a method to effectively detect the use of insulins in horses is required. Besides the readily available human insulin and its synthetic analogues, structurally similar insulins from other species can also be used a...
Stokes SM, Bertin FR, Stefanovski D, Belknap JK, Medina-Torres CE, Pollitt CC, van Eps AW.Hyperinsulinaemia is associated with the development of endocrinopathic laminitis; however, the mechanisms remain unclear. Objective: Evaluate the effects of hyperinsulinaemia on lamellar energy metabolism and perfusion during laminitis development. Methods: In vivo experiment. Methods: Eight Standardbred horses were instrumented with a microdialysis probe in the lamellae of a forelimb. A 24Â hours baseline period (BASELINE) was followed by 48Â hours of a continuous euglycaemic hyperinsulinaemic clamp (EHC) from 24 to 72Â hours (CLAMP). Microdialysate was collected every 6Â hours and analysed ...
Bashir ST, Ishak GM, Gastal MO, Roser JF, Gastal EL.Changes in intrafollicular growth factors and hormones were evaluated in vivo in postdeviation and impending ovulation follicles. Mares (n = 30) were randomly assigned to five experimental groups based on target diameters of 25, 30, 35, 40 mm, and impending signs of ovulation. Furthermore, data belonging to two or more proximal diameter groups that were not different were combined and regrouped for each factor separately. Follicular fluid-free insulin-like growth factor 1 was highest (P  0.05) among groups. Additionally, follicular fluid activin A tended (P < 0.06) to be higher in i...
Mendoza FJ, Aguilera-Aguilera R, Gonzalez-De Cara CA, Toribio RE, Estepa JC, Perez-Ecija A.Glucose-insulin dynamic challenges such as the intravenous glucose tolerance test (IVGTT) and combined glucose-insulin test (CGIT) have not been described in donkeys. The objectives of this study were (1) to characterize the IVGTT and CGIT in healthy adult donkeys, and (2) to establish normal glucose-insulin proxies. Sixteen donkeys were used and body morphometric variables obtained each. For the IVGTT, glucose (300 mg/kg) was given IV. For the CGIT, glucose (150 mg/kg) followed by recombinant insulin (0.1 IU/kg) were administered IV. Blood samples for glucose and insulin determinations were c...
de Laat MA, Fitzgerald DM, Sillence MN, Spence RJ.Equine insulin dysregulation (ID) is a common and poorly understood disorder that increases the risk of laminitis. Recent data show that the condition may be associated with alteration of the enteroinsular axis and enhanced glucose bioavailability. Upregulation of glucagon-like peptide-2 (GLP-2), an intestinotrophic peptide, leads to enhanced nutrient uptake and metabolic dysfunction in other species. Objective: The study aimed to 1) determine whether GLP-2 is differentially expressed in insulin-dysregulated ponies, compared with healthy ponies, and 2) confirm intestinal expression of the GLP-...
Bertin FR, Pader KS, Lescun TB, Sojka-Kritchevsky JE.To evaluate the effect of ovariectomy on insulin sensitivity in horses and determine whether the effects of suppression of the hypothalamo-pituitary-adrenal axis differ before and after ovariectomy. Methods: 6 healthy mares. Methods: The horses underwent an IV glucose tolerance test (IVGTT), an insulin sensitivity test, and a dexamethasone suppression test before and 5 weeks after ovariectomy. Body weight, serum cortisol and plasma ACTH concentrations, serum insulin-to-blood glucose concentration ratios, and changes in blood glucose concentration with time after injection of glucose or insulin...
Geor R, Frank N.Obesity, insulin resistance, hyperinsulinemia and hypertriglyceridemia are components of an equine metabolic syndrome phenotype associated with increased laminitis risk in horses. Links between these conditions and laminitis must still be elucidated, but human medicine provides candidate mechanisms for future study, including inflammation associated with obesity, vascular compromise induced by insulin resistance, and endothelial dysfunction. Just as metabolic syndrome has been linked to cardiovascular disease in humans, studies are now required to determine the exact mechanisms responsible for...
McCoy DJ.Both ovaries in a 10-year-old American Saddle Horse mare were determined to be larger than normal. The mare had problems with infertility during the preceding 3 years. Clinical evaluation revealed that the mare was polyuric, polydypsic, hyperinsulinemic, and hyperglycemic, and had reduced tolerance to exogenous glucose. Bilateral granulosa cell tumors were identified on histologic examination of the ovaries. The precise mechanism for the secondary diabetes mellitus was not determined; however, the cause was suspected to be a result of the synthesis and release of a hormonal substance by the tu...
Macon EL, Harris P, Bailey S, Caldwell Barker A, Adams A.Identifying intake levels of nonstructural carbohydrates (NSCs) that limit the postprandial insulinaemic response in the insulin dysregulated (ID) horse may help reduce hyperinsulinaemia-associated laminitis (HAL) risk. Objective: To determine if ID horses have thresholds for pure sources of starch and sugar, above which there is an augmented insulin response. Methods: Randomised crossover experiment. Methods: Fourteen adult horses (6 ID and 8 noninsulin dysregulated, NID; matched for bodyweight) were randomly fed eight dietary treatments. Dietary treatments were formulated using a base of low...
Kellon EM, Gustafson KM.Hyperinsulinemia associated with equine metabolic syndrome and pituitary pars intermedia dysfunction is a risk factor for laminitis. Research in other species has shown elevated body iron levels as both a predictor and consequence of insulin resistance. In humans, this is known as dysmetabolic hyperferritinemia. To explore the relationship between equine hyperinsulinemia and body iron levels. We reviewed case histories and laboratory results from an open access database maintained by the Equine Cushing's and Insulin Resistance Group Inc. (ECIR). We identified 33 horses with confirmed hyperinsu...
Fowden AL, Barnes RJ, Comline RS, Silver M.Insulin secretion and the factors influencing beta-cell function were investigated in the chronically catheterized fetal foal and mare during the second half of gestation. The response of the fetal beta cells to exogenous glucose was also examined. The mean concentration of insulin in the fetal foal was 7.5 +/- 0.5 (S.E.M.) microunit./ml (n = 20) which was significantly less than the corresponding maternal value of 49.0 +/- 5.0 microunit./ml (n = 20, P < 0.01). The insulin concentration in non-pregnant horses was 24.5 +/- 1.5 microunit./ml (n = 5) which was significantly less than the value...
Mills PC, Ng JC, Kramer H, Auer DE.Five clinically healthy Thoroughbred geldings were injected with Freund's adjuvant 3 times to induce a chronic inflammatory response. Blood was collected at various times before and after adjuvant administration. Clinical responses (rectal temperature and general demeanor) were also monitored. Adjuvant injection induced increases in rectal temperature and plasma fibrinogen concentration (maximum levels measured were mean +/- s.d. 39.7 +/- 0.5 degrees C and 8.2 +/- 0.3 g/l, respectively), indicative of an inflammatory response. A mild clinical depression was also observed in the horses for 24 h...
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...
Fessler JF, Bottoms GD, Roesel OF, Moore AB, Frauenfelder HC, Boon GD.A study was made of flunixin meglumine (FM), an analgesic agent with antiprostaglandin activity, in the management of endotoxin-induced changes in ponies. Three groups of 5 ponies each were used: A--controls, B--nontreated ponies with endotoxin-induced shock, and C--ponies with endotoxin-induced shock treated with FM. Shock was induced in anesthetized ponies with IV injections of Escherichia coli endotoxin. Disruption of glucose homeostasis, insulin levels, hemograms, aerobic metabolism, and cell damage as indicated by plasma enzymes were observed. Treatment with FM (5 minutes) after shock was...
Tiley HA, Geor RJ, McCutcheon LJ.To determine the effects of dexamethasone treatment on selected components of insulin signaling and glucose metabolism in skeletal muscle obtained from horses before and after administration of a euglycemic-hyperinsulinemic clamp (EHC). Methods: 6 adult Standardbreds. Methods: In a balanced crossover study, horses received either dexamethasone (0.08 mg/kg, IV, q 48 h) or an equivalent volume of saline (0.9% NaCl) solution, IV, for 21 days. A 2-hour EHC was administered for measurement of insulin sensitivity 1 day after treatment. Muscle biopsy specimens obtained before and after the EHC were a...
