Continuous intravenous infusion of glucose induces endogenous hyperinsulinaemia and lamellar histopathology in Standardbred horses

Pharmacologic Interventions to Immunologic and Immune-Mediated Conditions in Horses

Immunomodulators can stimulate, suppress, or regulate one or many aspects of the immune response. Use of a variety of immunostimulants, immunosuppressors, and anti-inflammatory drugs are described in horses, but the evidence supporting their efficacy is variable. Corticosteroids and nonsteroidal anti-inflammatory drugs are the best characterized immunomodulators in horses, but further study is needed to fully define their ideal dosing protocols and indications and to characterize the efficacy of other immunomodulators in equine medicine.

Systemic absorption of triamcinolone acetonide is increased from intrasynovial versus extrasynovial sites and induces hyperglycemia, hyperinsulinemia, and suppression of the hypothalamic-pituitary-adrenal axis

Steroid-associated laminitis remains a major concern with use of corticosteroids in horses. Individual case factors such as joint pathology, pre-existing endocrinopathies, or corticosteroid type, dose, and timing influencing steroid-induced laminitis risk have not been investigated. This study aimed to determine if systemic absorption of triamcinolone acetonide (TA) varies between intrasynovial (antebrachiocarpal) and extrasynovial (sacroiliac) injection sites, and to determine the effects of TA absorption on glucose, insulin, cortisol, and adrenocorticotropic hormone (ACTH). Twenty adult horses were randomized into antebrachiocarpal or sacroiliac joint injection groups, and each horse received bilateral injections with a total dose of 18 mg triamcinolone. Blood was collected prior to injection and at 1, 2, 4, 6, 8, 10, 12, 16, 20, 24, 36, 48, 60, and 72 h post-injection. Peak TA absorption occurred at 8 h in both groups, and was significantly higher in the intrasynovial group compared to the extrasynovial group (1.397 ng/mL, 0.672 ng/mL, p < 0.05). Plasma TA levels were significantly higher in the intrasynovial group from 8 to 36 h post-injection (p < 0.05). There was no difference in glucose, insulin, cortisol, or ACTH between groups at any time point. Insulin and glucose were significantly increased from baseline at all timepoints from 10-72 h and 1-72 h post-injection, respectively. Horses with elevated baseline insulin values (>20 μU/mL) from both groups experienced a more marked hyperinsulinemia, reaching a mean peak insulin of 197.5 μU/mL as compared to 90.06 μU/mL in those with normal baseline insulin. Cortisol and ACTH were significantly decreased from baseline at timepoints from 4-72 h post-injection in both groups. This study is the first to evaluate drug absorption from the sacroiliac site and demonstrates that drug absorption varies between intrasynovial and extrasynovial injection sites. TA absorption causes metabolic derangements, most notably a marked hyperinsulinemia that is more severe in horses with elevated baseline insulin values. The influence of baseline endocrinopathies on response to corticosteroid administration as well as the effect of corticosteroid-induced metabolic derangements warrant further investigation as risk factors for corticosteroid-associated laminitis.

Short-term induced hyperinsulinaemia and dexamethasone challenge do not affect circulating total adiponectin concentrations in insulin-sensitive ponies

BACKGROUND

Hypoadiponectinaemia is a risk factor for endocrinopathic laminitis, but the directionality and nature of its association with insulin dysregulation is unclear.

OBJECTIVES

To investigate the effects of short-term induced hyperinsulinaemia and dexamethasone challenge on circulating [total adiponectin] and whole blood expression of adiponectin (AdipoR1 and AdipoR2), insulin, and insulin-like growth factor 1 (IGF-1) receptors in insulin-sensitive ponies.

STUDY DESIGN

In vivo experiment.

METHODS

Six never-laminitic, insulin-sensitive, native-breed UK ponies first underwent a dexamethasone challenge (0.08 mg/kg i.v.) with blood samples collected every 15 min over 3 h. After a 14-day washout period, hyperinsulinaemia was induced for 9 h via a euglycaemic-hyperinsulinaemic clamp (EHC), with blood samples collected every 30 min. Serum [insulin], plasma [total adiponectin], and plasma [IGF-1] were measured using validated assays and receptor gene expression was assessed via quantitative polymerase chain reaction (qPCR). Finally, whole blood was incubated with 10-1000 ng/mL dexamethasone for 3 h at 37°C to investigate its direct effects on gene expression.

RESULTS

There were no adverse effects observed during either protocol. Dexamethasone challenge did not alter circulating [insulin] or [total adiponectin] at any time-point, but significantly upregulated AdipoR1 and IGF-1R expression at 150 and 180 min. Ex vivo incubation of whole blood with dexamethasone did not alter expression of the genes examined. There was no change in [total adiponectin] or expression of the genes examined associated with EHC-induced hyperinsulinemia.

MAIN LIMITATIONS

This was a small sample size that included only native-breed ponies; total adiponectin was measured rather than high-molecular-weight adiponectin.

CONCLUSIONS

Short-term induced hyperinsulinaemia and dexamethasone challenge did not affect circulating [total adiponectin] in insulin-sensitive ponies. However, dexamethasone administration was associated with upregulation of two receptors linked to adiponectin signalling, suggesting that a physiological response occurred possibly to counteract dexamethasone-associated changes in tissue insulin sensitivity.

Comparison of one novel and four established diagnostic tests for insulin dysregulation in ponies

Several tests have been advocated for diagnosis of insulin dysregulation (ID). Tests using simple sugars may not reflect the response to naturally ingested carbohydrates. This study aimed to evaluate agreement between the oral glucose test (OGT), the oral sugar test (OST), a novel oral test using a proprietary cereal (WEET), the IV combined glucose-insulin tolerance test (CGIT) and fasted basal insulin (FI) for diagnosis of ID. Each of the five tests above was performed on a group of six normal and six insulin dysregulated mixed-breed ponies in a randomised crossover study. Area under the curve (AUC) and maximum concentration of insulin from OGT, OST and WEET showed strong to very strong bivariate correlations (r = 0.85-0.94, and r = 0.87-0.92, respectively; P ≤ 0.001) and were significantly different between tests (associated with dose of carbohydrate) and between CGIT-positive and -negative ponies. Dichotomous results showed substantial agreement between OST and both WEET (κ = 0.65; P = 0.02) and OGT (κ = 0.67; P = 0.01) and between CGIT and both OST (κ = 0.63; P = 0.03) and OGT (κ = 0.67; P = 0.01), and no agreement between FI, which had low sensitivity, and all other tests (κ = 0.15 - 0.31; P > 0. 05). Palatability of WEET was variable, resulting in one pony being excluded for analysis of WEET data. Further work on development of an oral test using a more palatable feedstuff and appropriate cut-offs or diagnostic thresholds for tests of ID is warranted.

Effect of micronization and meal size of corn grain on glycemic response and in vitro hindgut acidosis potential in horses

This study aimed to 1) evaluate the interaction of corn grain micronization and starch levels per meal on equine plasma glucose, and 2) determine if micronization affects the risk of hindgut acidosis. Six mature (aged 6 to 10 years), healthy, non-pregnant mares (initial body weight [BW]: 301 to 463 kg) were used in a 2×3 factorial cross-over design. The treatments included two forms of corn grain (ground and micronized flaked) at three levels of starch (1, 1.5, and 2 g/kg BW per meal). The blood was sampled before and 30, 60, 90, 120, 180, 240, and 300 min after morning feeding and the glucose concentration in the plasma was determined. Small intestine and hindgut dry matter (DM) disappearances of ground and micronized corn were also compared using in vitro techniques. Micronized flaked corn grain showed three times more in vitro enzymatic DM disappearance (p < 0.001) compared with ground corn. Residues of in vitro enzymatic digestion of micronized flaked corn fermented 38.59 % faster than ground corn during in vitro hindgut incubation. The horses that consumed micronized flaked corn had higher post-prandial plasma glucose concentrations (p < 0.001). Increasing starch levels per meal from 1-2 g/kg BW resulted in higher plasma glucose concentrations (P = 0.005). However, no interaction of processing and starch meal size was found. Overall, processing the corn grain by micronization or increasing starch level per meal increased the plasma glucose concentrations, but the magnitude of the increases did not match that expected from in vitro studies.

Evaluation of field-testing protocols to diagnose insulin dysregulation in ponies using a Bayesian approach

Field tests and their association with laminitis have not been evaluated in large cohorts. The objectives of this study were to evaluate the performance of basal insulin (BI), the oral sugar test (OST) and the insulin tolerance test (ITT) to diagnose ID and investigate their association with laminitis. Insulin dysregulation status was determined in 146 ponies using BI (insulin concentration >20 µIU/mL), an OST (insulin concentration >65 µIU/mL at 60 or 90 min after oral administration of 0.45 mL/kg corn syrup) and an ITT (< 50% reduction in glucose concentration 30 min after intravenous administration of 0.1 IU/kg insulin). Laminitis was identified using modified-Obel scores. A Bayesian approach was used to define the characteristics of the tests and receiver operating characteristic curves were used to assess their association with laminitis. All tests were well tolerated and laminitis was diagnosed in 9% of ponies. Insulin dysregulation was diagnosed in 15% of ponies using BI, 38% using the OST and 54% using the ITT with 11% of ponies positive for all three tests. The sensitivities and specificities of BI, the OST and the ITT to diagnose ID were 0.52 (95% confidence interval [CI], 0.35-0.79) and 0.97 (95% CI, 0.91 - 1.00), 0.84 (95% CI, 0.70 - 0.94) and 0.60 (95% CI, 0.49 - 0.71), and 0.85 (95% CI, 0.68-0.96) and 0.88 (95% CI, 0.75 - 0.97), respectively. Only BI and the OST were associated with laminitis (P = 0.003 and 0.015, respectively).

A review of cellular and molecular mechanisms in endocrinopathic, sepsis-related and supporting limb equine laminitis

Equine laminitis has both fascinated and frustrated veterinary researchers and clinicians for many years. The recognition that many ponies suffering from pasture-associated laminitis have an insulin-dysregulated phenotype (endocrinopathic laminitis, EL) and that prolonged insulin and glucose infusions can experimentally induce laminar pathology and functional failure are seminal discoveries in this field. Researchers have studied the molecular basis for disease pathogenesis in models of EL, sepsis-related laminitis and supporting limb laminitis and generated much data over the last 15 years. This review attempts to synthesise those data, drawing comparisons between models and naturally occurring laminitis. A hypothesis is proposed that the basal epithelial cell stress is a central event in each category of laminitis. Furthermore, in naturally occurring pasture-associated laminitis, pathways that predominate in each type of laminitis contribute to laminar lamellar pathology to varying extents. Based on the molecular mechanisms determined in experimental models, interactions between these pathways are identified.

Effect of sirolimus on insulin dynamics in horses

BACKGROUND

Sirolimus, a mechanistic target of rapamycin inhibitor, suppresses insulin production in other species and has therapeutic potential for hyperinsulinemia in horses.

HYPOTHESIS/OBJECTIVE

Determine the pharmacokinetics (PKs) of sirolimus and evaluate its effect on insulin dynamics in healthy and insulin dysregulation (ID) horses.

ANIMALS

Eight Standardbred geldings.

METHODS

A PK study was performed followed by a placebo-controlled, randomized, crossover study. Blood sirolimus concentrations were measured by liquid chromatography-mass-spectrometry. PK indices were estimated by fitting a 2-compartment model using nonlinear least squares regression. An oral glucose test (OGT) was conducted before and 4, 24, 72, and 144 hours after administration of sirolimus or placebo. Effects of time, treatment and animal on blood glucose and insulin concentrations were analyzed using mixed-effects linear regression. Sirolimus was then administered to 4 horses with dexamethasone-induced ID and an OGT was performed at baseline, after ID induction and after 7 days of treatment.

RESULTS

Median (range) maximum sirolimus concentration was 277.0 (247.5-316.06) ng/mL at 5 (5-10) min and half-life was 3552 (3248-4767) min. Mean (range) oral bioavailability was 9.5 (6.8-12.4)%. Sirolimus had a significant effect on insulin concentration 24 hours after a single dose: median (interquartile range) insulin at 60 min (5.0 [3.7-7.0] μIU/mL) was 37 (-5 to 54)% less than placebo (8.7 [5.8-13.7] μIU/mL, P = .03); and at 120 min (10.2 [8.4-12.2] μIU/mL) was 28 (-15 to 53)% less than placebo (14.9 [8.4-24.8] μIU/mL, P = .02). There was minimal effect on glucose concentration. Insulin responses decreased toward baseline in ID horses after 7 days of treatment.

CONCLUSION AND CLINICAL IMPORTANCE

Sirolimus decreased the insulinemic response to glucose and warrants further investigation.

A glucagon-like peptide-1 receptor antagonist reduces the insulin response to a glycemic meal in ponies

High plasma concentrations of insulin can cause acute laminitis. Ponies and horses with insulin dysregulation (ID) exhibit marked hyperinsulinemia in response to dietary hydrolyzable carbohydrates. Glucagon-like peptide-1 (GLP-1), an incretin hormone released from the gastrointestinal tract, enhances insulin release, and is increased postprandially in ponies with ID. The aim of this study was to determine whether blocking the GLP-1 receptor reduces the insulin response to a high glycemic meal. Five adult ponies were adapted to a cereal meal and then given two feed challenges 24 h apart of a meal containing 3 g/kg BW micronized maize. Using a randomized cross-over design all ponies received both treatments, where one of the feeds was preceded by the IV administration of a GLP-1 receptor blocking peptide, Exendin-3 (9-39) amide (80 µg/kg), and the other feed by a sham treatment of peptide diluent only. Blood samples were taken before feeding and peptide administration, and then at 30-min intervals via a jugular catheter for 6 h for the measurement of insulin, glucose, and active GLP-1. The peptide and meal challenge caused no adverse effects, and the change in plasma glucose in response to the meal was not affected (P = 0.36) by treatment: peak concentration 9.24 ± 1.22 and 9.14 ± 1.08 mmol/L without and with the antagonist, respectively. Similarly, there was no effect (P = 0.35) on plasma active GLP-1 concentrations: peak concentration 14.3 ± 1.36 pM and 13.7 ± 1.97 pM without and with the antagonist, respectively. However, the antagonist caused a significant decrease in the area under the curve for insulin (P = 0.04), and weak evidence (P = 0.06) of a reduction in peak insulin concentration (456 ± 147 μIU/mL and 370 ± 146 μIU/mL without and with the antagonist, respectively). The lower overall insulin response to the maize meal after treatment with the antagonist demonstrates that blocking the GLP-1 receptor partially reduced insulin production in response to a high starch, high glycemic index, diet. Using a different methodological approach to published studies, this study also confirmed that GLP-1 does contribute to the excessive insulin production in ponies with ID.

A one-health lens offers new perspectives on the importance of endocrine disorders in the equine athlete

Endocrine disorders are associated with joint pain and tendon injury in humans, but the effects in the horse are only starting to be understood. Similar patterns of clinical signs and injury appear to affect horses and humans for both orthopedic and endocrine disorders, supporting the use of a one-health approach to tackle these issues. In this Currents in One Health, we will discuss common equine endocrinopathies, current testing recommendations, dietary management, genetic predispositions, and endocrine disorders' effects on performance. Our aim is to use a one-health lens to describe current comparative research so that veterinarians can employ cutting-edge preventative, diagnostic, and therapeutic recommendations. Identified key gaps in knowledge include whether equine metabolic osteoarthritis exists, if steroid joint injections are safe in horses with endocrine disorders, and if the return to performance percentage improves with concurrent treatment of endocrine and musculoskeletal disorders. Key takeaways include that the relationship between endocrine disorders and musculoskeletal disease in the horse goes beyond laminitis to include lameness, muscle atrophy, suspensory ligament degeneration, osteochondritis dissecans, and potentially metabolic osteoarthritis. Approaches learned from human and equine comparative studies can offer insight into injury recognition and management, thus mitigating the impact of endocrine disorders on performance in both species. Readers interested in an in-depth description of current and future research involving pathophysiology, novel interventions, and multiomic approaches to identify individuals with athletic limitations induced by endocrine disorders are invited to read the companion Currents in One Health by Manfredi et al, AJVR, February 2023.

Evaluation of peripheral blood polymorphonuclear cell functions after an oral carbohydrate overload in obese and insulin dysregulated horses

Obesity and insulin dysregulation (ID) are increasingly prevalent conditions in equid populations worldwide. Immune impairment is well described in humans with metabolic dysfunction and is reported but still incompletely understood in horses. This study evaluated the effect of acute induced transient hyperglycemia on apoptosis, phagocytosis and oxidative burst activity of peripheral blood polymorphonuclear cells (PMN) of lean and obese adult horses with or without insulin dysregulation. Seventeen adult horses were allocated into three groups based on their body condition score (BCS) and metabolic status: lean-insulin sensitive (lean-IS), obese-insulin sensitive (obese-IS) and obese-insulin dysregulated (obese-ID). ID was determined by insulin tolerance testing (ITT). Blood glucose elevation was induced through an infeed-oral glucose test (in-feed OGT), and all assessments of PMN functions (apoptosis, phagocytosis and oxidative burst) were done in vitro after isolation from peripheral blood before and 120 min after carbohydrate overload. Results were analyzed using a repeated measures linear mixed model with significance defined at P < 0.05. No differences in apoptosis were observed between experimental groups at any time point. Phagocytic capacity was significantly lower at baseline in the obese-ID group but increased in response to glucose administration when compared to the other two groups. Basal reactive oxygen species production in the obese-IS group differed significantly from the lean-IS and obese-ID groups and decreased significantly in response to glucose administration. Results from this study showed that both metabolic status itself, and oral glucose administration, seem to be factors that alter PMN functionality in horses, specifically phagocytosis and oxidative burst.

Obesity-Related Metabolic Dysfunction in Dairy Cows and Horses: Comparison to Human Metabolic Syndrome

Obesity has become a serious health problem with frequent occurrence both in human and animal populations. It is estimated that it may affect over 85% of the human population and 70–80% of horses and cows by 2030. Fat cow syndrome (FCS) is a combination of metabolic, digestive, infectious, and reproductive disorders that affects obese periparturient dairy cows, and occurs most frequently in loose-housing systems, where periparturient and dry cows are fed and managed in one group disregarding the lactation stages. Equine metabolic syndrome (EMS) was named after human metabolic syndrome (MetS) and has insulin dysregulation as a central and consistent feature. It is often associated with obesity, although EMS may occur in a lean phenotype as well. Other inconsistent features of EMS are cardiovascular changes and adipose dysregulation. Laminitis is the main clinical consequence of EMS. MetS holds a 30-years old lead in research and represents a clustering of risk factors that comprise abdominal obesity, dyslipidemia, hypertension, and hyperglycemia (impaired fasting glucose or type 2 diabetes mellitus—T2DM), which are associated with doubled atherosclerotic cardiovascular disease risk, and a 5-fold increased risk for T2DM. The main aim of this review is to provide critical information for better understanding of the underlying mechanisms of obesity-related metabolic dysfunction in animals, especially in cows and horses, in comparison with MetS. Human medicine studies can offer suitable candidate mechanisms to fill the existing gap in the literature, which might be indispensable for owners to tackle FCS, EMS, and their consequences.

Endocrinopathic Laminitis

Endocrinopathic laminitis (EL) primarily occurs because of insulin dysregulation (ID) mediated through downstream effects of insulin on IGF-1R in lamellar tissues. There is likely contributing vascular and metabolic dysfunction within the lamellae, but EL is relatively non-inflammatory. EL is associated with lamellar stretching, proliferation, and failure, ultimately causing failure of the suspensory apparatus of the distal phalanx. Proper education regarding mitigating risk factors makes this a largely preventable cause of laminitis. Annual hoof evaluation plus screening geriatric horses for pituitary pars intermedia dysfunction and ID, and younger horses for ID, can significantly decrease the incidence of this devastating condition.

"Feeding the Foot": Nutritional Influences on Equine Hoof Health

Nutrition plays an important role in equine health, including that of the foot. Deficiencies and excesses of dietary components can affect the growth and function of the foot and have been associated with important podiatric diseases. The recognition, prevention, and treatment of specific notable nutritional diseases of the foot are discussed, as well as information regarding specific ingredients included in supplements meant to improve equine hoof quality. Ensuring provision of a balanced diet, maintaining horses in appropriate body condition, and seeking guidance from an equine nutritionist when creating dietary recommendations will prevent most equine foot disease related to nutrition.

Plasma amino acid concentrations during experimental hyperinsulinemia in 2 laminitis models

BACKGROUND

Endocrinopathic laminitis develops in association with insulin dysregulation, but the role of insulin in the pathogenesis remains unclear. Hyperinsulinemia can cause hypoaminoacidemia, which is associated with integumentary lesions in other species and therefore warrants investigation as a potential mechanism in laminitis.

OBJECTIVE

Evaluate plasma amino acid concentrations in the euglycemic-hyperinsulinemic clamp (EHC) and prolonged glucose infusion (PGI) laminitis models.

ANIMALS

Sixteen Standardbred horses.

METHODS

Prospective experimental study. Plasma amino acid concentrations were measured in samples collected every 6 hours from horses that underwent a 48-hour EHC (n = 8) or 66-hour PGI (n = 8) after a 24- or 6-hour baseline period in EHC and PGI groups, respectively.

RESULTS

Fifteen of the 20 measured amino acid concentrations decreased over time in both EHC and PGI horses (P < 0.001). The median percentage change from baseline for these amino acids was: histidine (EHC: 41.5%; PGI: 43.9%), glutamine (EHC: 51.8%; PGI: 35.3%), arginine (EHC: 51.4%; PGI: 41%), glutamic acid (EHC: 52.4%; PGI: 31.7%), threonine (EHC: 62.8%; PGI: 25.2%), alanine (EHC: 48.9%; PGI: 19.5%), proline (EHC: 56.2%; PGI: 30.3%), cystine (EHC: 34.9%; PGI: 31.2%), lysine (EHC: 46.4%; PGI: 27.8%), tyrosine (EHC: 27.5%; PGI: 16.9%), methionine (EHC: 69.3%; PGI: 50.8%), valine (EHC: 50.8%; PGI: 34.4%), isoleucine (EHC: 60.8%; PGI: 38.7%), leucine (EHC: 48.2%; PGI: 36.6%), and phenylalanine (EHC: 16.6%; PGI: 12.1%).

CONCLUSIONS AND CLINICAL IMPORTANCE

Hypoaminoacidemia develops in EHC and PGI laminitis models. The role of hypoaminoacidemia in the development of hyperinsulinemia-associated laminitis warrants further investigation.

Pituitary Pars Intermedia Dysfunction and Metabolic Syndrome in Donkeys

Simple Summary

Donkeys are one of the six species of the equid family. Even though they may look similar to horses, there are optical, behavioral, and physiological differences between the two species. The most important endocrine diseases in horses (equine metabolic syndrome and pituitary pars intermedia dysfunction: PPID) also exist in donkeys. The key symptoms of asinine metabolic syndrome (AMS), similar to horses, are obesity, insulin dysregulation, and laminitis. It can be diagnosed with either basal glucose and insulin concentration or dynamic tests. The intravenous glucose tolerance test and the combined glucose insulin tolerance test were evaluated for donkeys. The therapy of AMS is aimed at weight and exercise management. Donkeys suffering from PPID are often laminitic. Other authors have reported on hypertrichosis as a cardinal sign. Donkey-specific differences in shedding compared to horses have to be considered. The PPID can be diagnosed with donkey-specific reference values or dynamic testing. The dexamethasone suppression test, the thyrotropin releasing hormone (TRH) test, and the combined dexamethasone suppression/TRH test were evaluated for donkeys.

Abstract

Appropriate medical care for donkeys is challenging despite being important working animals in non-industrialized countries and pets in first world countries. Although the same principles of diagnosis and therapy as in horses are commonly applied, there are differences in reference values and physiologic reaction to dynamic tests. However, donkeys seem to suffer from typical equine diseases, such as metabolic syndrome and pituitary pars intermedia dysfunction (PPID). Asinine metabolic syndrome (AMS) comprises obesity, insulin dysregulation, and laminitis. The principles of diagnosis are similar to horses. Donkey-specific reference ranges for insulin and glucose have been evaluated previously. Examinations regarding dynamic testing revealed differences in the intravenous glucose tolerance test and the combined insulin tolerance test compared to horses. The therapy of AMS is based mainly on weight loss and exercise. There are conflicting data regarding the incidence of PPID in donkeys. Laminitis and hypertrichosis were described as the main clinical signs. Species-specific and seasonal reference ranges were defined to diagnose PPID in donkeys. Furthermore, the dexamethasone suppression test, the thyrotropin releasing hormone (TRH) test and the combined dexamethasone suppression/TRH test were evaluated. Pergolide is commonly recommended for treatment.

Genetics and Signaling Pathways of Laminitis

Laminitis is a devastating disease with diverse etiologies and few, if any, effective treatments. Gene expression and hypothesis-generating genomic studies have provided a fresh look at the key molecular players at crucial timepoints in diverse experimental and naturally affected tissues. We summarize findings to date, and propose a unifying model of the laminitis disease process that includes several pathogenesis concepts shared with other diseases of epidermal and epithelial tissues. The value of these new pathways as potential therapeutic targets is exciting but will require careful future work to validate new methods and launch systematic clinical trials.

Investigation of the Effects of a Dietary Supplement on Insulin and Adipokine Concentrations in Equine Metabolic Syndrome/Insulin Dysregulation

High insulin concentrations are a common clinical feature of equine metabolic syndrome (EMS) and insulin dysregulation. Hyperinsulinemia can induce laminitis, so reduction of insulin concentrations in response to an oral challenge should decrease risk. In human studies, diets containing a polyphenol (resveratrol) led to improvements in insulin sensitivity. In rodents, the addition of leucine to a resveratrol supplement caused a decrease in the amount of resveratrol needed to achieve a clinical effect. We hypothesize a supplementation with a low dose of a synergistic polyphenol and amino acid blend including leucine (SPB+L) would improve metabolic health in EMS/insulin dysregulated horses. Fifteen EMS/ID horses received a high or low dose of SPB+ L daily for 6 weeks. Insulin during an oral sugar test (OST), body condition score, weight, baseline high-molecular-weight (HMW) adiponectin, triglycerides, nonesterified fatty acids, and tumor necrosis factor alpha were assessed before supplementation (PRE) and after supplementation (POST) via paired Student's t-tests and a repeated-measures mixed-model analysis of variance (significant at P < .05). There were no differences between doses. Horses in the POST group weighed significantly less, had significantly higher baseline HMW adiponectin concentrations, and had significantly lower insulin concentrations at 60- and 75-minute time points (P < .05). Insulin concentrations of the horsesin the POST group, but not in the PRE group, were lower and similar to results from the study conducted three years before the present study (PRIOR) for 0- and 60-minute time points (P < .002). An increased HMW adiponectin level supports increasing insulin sensitivity after supplementation. These results suggest that SPB + L supplementation at either dose leads to improvements in the clinical manifestations of EMS/insulin dysregulation, potentially reducing laminitis risk.

Relação espacial entre o estojo córneo e a falange distal em éguas Campolina adultas com e sem obesidade

RESUMO A laminite endocrinopática tem acometido um número crescente de equinos com sinais de obesidade. Em um estudo recente com fêmeas jovens (até cinco anos) da raça Campolina, demonstraram-se indícios de alterações no dígito, ainda discretas, aparentemente associadas ao aumento da adiposidade. Com a hipótese de que essa associação é mais evidente em animais em faixa etária superior, o objetivo do presente estudo foi estudar éguas adultas (acima de cinco anos) da raça Campolina com e sem obesidade, avaliando-se radiograficamente a relação espacial entre estojo córneo e falange distal. Foram utilizadas 27 éguas entre seis e 14 anos de idade, sendo analisadas variáveis de adiposidade e medidas radiográficas dos cascos dos membros torácicos de equinos com escore corporal de 5 a 7/9 (grupo controle) e de 8 a 9 (grupo obeso). Foram feitas comparações entre os grupos e correlacionaram-se as variáveis de adiposidade com variáveis casco. A distância de afundamento da falange distal foi cerca de 20% superior nas éguas obesas (12,3±2,5 contra 10,2±2,2mm no grupo controle). Esse parâmetro também correlacionou (P<0,01) com vários parâmetros de adiposidade, com destaque para o escore de condição corporal (r=0,47) e a circunferência de pescoço a 75% (r=0,42). Os resultados corroboram estudos prévios que demonstraram associação entre obesidade e indícios de separação entre falange distal e estojo córneo em equinos de raças nacionais, comprovando, assim, a utilidade da avaliação radiográfica nesses animais. Em conclusão, éguas da raça Campolina com obesidade possuem alterações evidentes na relação espacial entre estojo córneo e falange distal, que se intensificam com o aumento da idade e da adiposidade.

The effect of different grazing conditions on the insulin and incretin response to the oral glucose test in ponies

BACKGROUND

The oral glucose test (OGT) is a useful tool for diagnosing insulin dysregulation (ID) and is somewhat repeatable in ponies under consistent management. This study aimed to determine whether the insulin and incretin responses to an OGT in ponies differed after short-term access to fertilised pasture, compared to unfertilised pasture, by using a randomised, repeated measures study design. Sixteen mixed-breed ponies were classified as severely insulin-dysregulated (SD; post-prandial insulin ≥80 μIU/mL) or not severely insulin-dysregulated (NSD; post-prandial insulin < 80 μIU/mL) using an OGT prior to the study. The ponies accessed pasture that was fertilised, or unfertilised, for 5 days (4 h/day, with supplemental hay provided at 0.7% bodyweight), with a 10 day period between phases. An OGT was performed after each phase. Glucose, insulin, active glucagon-like peptide-1 (aGLP-1), and glucose-dependent insulinotropic polypeptide (GIP) were measured in post-prandial blood samples.

RESULTS

The volume of fertilised pasture was five-fold greater than unfertilised pasture, with % non-structural carbohydrates (NSC) similar between all forages. Consuming fertilised pasture increased (P = 0.018) the serum insulin response to an OGT, compared to grazing unfertilised pasture. A limitation of the study was that pasture intake was unable to be quantified. Insulin responses were greater in SD, compared to NSD, ponies (P < 0.001) and remained well above the test cut-off at all times. A subset of ponies, initially screened as NSD, became (more) insulin-dysregulated after pasture access. Further, aGLP-1 was a significant predictor of insulin concentration in this cohort.

CONCLUSIONS

Whereas some insulin-dysregulated ponies were comparatively resistant to dietary intervention, others showed markedly different OGT responses following subtle changes in their forage-based diet. This implies that mild/early ID might be unmasked by dietary change, and that dietary management is important in these ponies. However, dietary management alone may not be adequate for all cases of ID.

From Table to Stable: A Comparative Review of Selected Aspects of Human and Equine Metabolic Syndrome

Obesity data in people and companion animals are depicting a future of increasing morbidity, cost for society, and significant health and welfare concerns. Between 25 and 50% of cats, dogs, and horses in developed countries are overweight or obese, which mirrors the situation in humans. Equine metabolic syndrome (EMS) was named after human metabolic syndrome (MetS), which has about 30 years of lead in research efforts. Even though the complications of the two syndromes seem to grossly differ (cardiac vs. laminitis risk), a number of similar disease mechanisms are worthy of investigation. Since the first EMS consensus statement by the American College of Veterinary Internal Medicine in 2010, numerous studies have confirmed the link between insulin dysregulation and laminitis, even though the mechanisms are not fully understood. After the discovery of the role of adipokines in MetS, evidence about inflammatory mechanisms related to adiposity in rodent models, companion animals, horses, and humans is constantly increasing. Oxidative and dicarbonyl stress have been correlated with insulin dysregulation, obesity, and recently with laminitis. Vascular actions of insulin through nitric oxide, endothelin-1, and other mechanisms are being studied in horses and can provide a better understanding of laminitis pathophysiology. More research is needed on neuropathic mechanisms in insulin-dysregulated horses, which could be important in the pathogenesis of laminitis and laminitic pain. Human literature can provide viable material for novel studies in areas that have received limited attention, in addition to being valuable information for clients about the consequences of unhealthy management of their horses.

Are There Shared Mechanisms in the Pathophysiology of Different Clinical Forms of Laminitis and What Are the Implications for Prevention and Treatment?

Laminitis is a consequence of primary disease processes elsewhere in the body. The key pathophysiologic events are insulin dysregulation in endocrinopathic laminitis, ischemia in supporting limb laminitis, and inflammation in sepsis-related laminitis. These apparently disparate mechanisms converge to cause lamellar attachment failure through epithelial cell adhesion loss and stretch, possibly mediated by common growth factor signaling pathways. Tissue damage through mechanical distraction, inflammation, pain, and a proliferative epithelial healing response are features of acute laminitis regardless of the cause. Preventive and treatment strategies based on knowledge of these unique and common mechanistic events are likely to improve clinical outcomes.

ECEIM consensus statement on equine metabolic syndrome

Equine metabolic syndrome (EMS) is a widely recognized collection of risk factors for endocrinopathic laminitis. The most important of these risk factors is insulin dysregulation (ID). Clinicians and horse owners must recognize the presence of these risk factors so that they can be targeted and controlled to reduce the risk of laminitis attacks. Diagnosis of EMS is based partly on the horse's history and clinical examination findings, and partly on laboratory testing. Several choices of test exist which examine different facets of ID and other related metabolic disturbances. EMS is controlled mainly by dietary strategies and exercise programs that aim to improve insulin regulation and decrease obesity where present. In some cases, pharmacologic aids might be useful. Management of an EMS case is a long‐term strategy requiring diligence and discipline by the horse's carer and support and guidance from their veterinarians.

Characterization of insulin and IGF-1 receptor binding in equine liver and lamellar tissue: implications for endocrinopathic laminitis

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-1R. To investigate this possibility, cell membrane fragments containing IGF-1R were extracted from the livers of 6 horses and the lamellae of >50 horses euthanized for nonresearch purposes at an abattoir. Radioligand-binding studies using ¹²⁵I-IGF-1 and ¹²⁵I-insulin confirmed an abundance of high-affinity IGF-1R in the liver (K_D 0.11 nM, B_max 223 fmol/mg protein) and lamellae (K_D 0.16 nM, B_max 243 fmol/mg protein). However, the affinity of insulin for binding to the lamellar IGF-1R (K_i 934 nM) was >5,800 fold less than that of IGF-1, suggesting that insulin is unlikely to bind to equine IGF-1R at physiological concentrations. Although insulin receptors could be detected in the liver (K_D 0.48 nM, B_max 123 fmol/mg protein), they were barely detectable in lamellae (estimated B_max 14 fmol/mg protein). There was no evidence to support the presence of insulin/IGF-1 hybrid receptors in either tissue. These findings suggest that insulin does not act directly through IGF-1 receptors and that an alternative theory is required to explain the mechanism of insulin action in laminitis.

Insulin and incretin responses to grazing in insulin-dysregulated and healthy ponies

Background

Supraphysiological insulin and incretin responses to a cereal‐based diet have been described in horses and ponies with insulin dysregulation (ID). However, the hormonal responses to grazing have not yet been described.

Objectives

To determine if there is a difference in the insulin and incretin responses to grazing pasture between insulin‐dysregulated and healthy ponies.

Animals

A cohort of 16 ponies comprising 5 with normal insulin regulation (NIR), 6 with moderate ID (MID), and 5 with severe ID (SID).

Methods

In this case‐control study, an oral glucose test (OGT) was used to determine the insulin responsiveness of each pony to PO carbohydrate before grazing pasture (4 hours) for 3 consecutive days. Serial blood samples collected during grazing were analyzed for glucose, insulin, glucose‐dependent insulinotropic peptide (GIP) and active glucagon‐like peptide‐1 (aGLP‐1), and compared among pony groups and day of pasture access.

Results

The area under the insulin curve when grazing increased with ID severity (P < .03). The median (range) maximal insulin concentration was greater in the MID (72.5 [129] μIU/mL) and SID (255 [338.5] μIU/mL) groups, compared to the NIR (11.7 [24.9] μIU/mL) group (P < .03) and occurred within 2‐4 hours of grazing. Postprandial OGT insulin concentration was positively correlated with 2 hours post‐grazing insulin across all 3 grazing days (P ≤ .03). The aGLP‐1 and GIP concentrations increased in response to grazing but did not differ among groups.

Conclusions and Clinical Importance

Grazing pasture provoked an increased insulin and incretin response in insulin‐dysregulated ponies within 4 hours of grazing. The pasture and OGT insulin concentrations were correlated.

Ex vivo effects of insulin on the structural integrity of equine digital lamellae

BACKGROUND

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.

OBJECTIVES

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.

STUDY DESIGN

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 insulin. Lamellar explants comprised of hoof wall, lamellar tissue and distal phalanx were harvested from four adult horses with no evidence of inflammatory disease or pre-existing disease of the digit. Following an equilibration period, explants were incubated in medium or medium supplemented with insulin (2.5 μg/ml) for 8 h prior to biomechanical testing to obtain load (N), stress (MPa), elongation to failure (mm), and Young's modulus (MPa) for each explant. Significant differences were assessed using a mixed linear model with horses as a random factor and control or insulin-treated group as a fixed factor.

RESULTS

Lamellar explants incubated in medium supplemented with insulin failed at significantly lower load (P = 0.0001) and lower stress (P = 0.001) and had greater elongation to failure (P = 0.02).

MAIN LIMITATIONS

In addition to the ex vivo nature of the study, location-dependent variability in explant structural integrity and variable diffusion of nutrients due to explant size may have been limitations. However, the study design attempted to account for these limitations through random assignment of explants to treatment groups independent of location and by evaluating stress to failure.

CONCLUSIONS

Insulin weakens the structural integrity of equine lamellar explants and an ex vivo model for evaluation of hyperinsulinaemia-induced lamellar failure was established. The summary is available in Spanish - see Supporting Information.

The oral glucose test predicts laminitis risk in ponies fed a diet high in nonstructural carbohydrates

The aim of this study was to investigate the relationship between laminitis development in ponies and insulin/glucose concentrations in response to the oral glucose test (OGT) and a dietary challenge high in nonstructural carbohydrates (NSCs). After undergoing an OGT (1 g dextrose/kg BW in feed), 37 ponies with 2-h serum insulin concentrations ranging from 22 to 1,133 μIU/mL were subjected to a diet challenge period (DCP), consuming 12 g NSC/kg BW/d for up to 18 d. Insulin and glucose responses were measured on day 2 of the DCP. Clinical laminitis was diagnosed by blinded experts and confirmed radiographically. Basal ACTH levels and clinical signs were assessed to investigate concurrent putative pituitary pars intermedia dysfunction (PPID). The diet induced Obel grade 1 or 2 laminitis in 14 ponies (38%). The ponies that developed laminitis had higher maximum concentrations of blood glucose (P = 0.04) and serum insulin (P = 0.02) in response to the diet. The geometric mean (95% CI) blood glucose concentration for laminitis cases was 14.9 (12.9-17.2) mM, compared to 10.7 (9.2-12.5) mM for ponies who did not develop laminitis. Similarly, the geometric mean (95% CI) for serum insulin was 396 (301-520) μIU/mL for laminitis cases, compared to 216 (148-316) μIU/mL for ponies who did not develop laminitis. Laminitis incidence was likewise associated with insulin concentrations measured during the OGT. Laminitis occurred at frequencies of 0% (0/7) if postdextrose insulin (μIU/mL) was <50; 35% (8/23) if insulin was 50 to 195; and 86% (6/7) if insulin was >195 μIU/mL. Basal ACTH concentrations were above seasonally accepted reference ranges in 16/37 ponies, and 8 of these animals (50%) developed laminitis. This included all 5 ponies in the study that had clinical signs of PPID (100%). In contrast, hyperinsulinemia and laminitis occurred in only 3/11 ponies (27%) with elevated ACTH concentrations and no clinical signs of PPID (P = 0.009). Thus, laminitis occurrence was associated with higher glucose and insulin responses to both the OGT and challenge diet, and the frequency of laminitis can be predicted based on insulin and glucose hyperresponsiveness to these oral carbohydrate challenges.

Metabolic perturbations in Welsh Ponies with insulin dysregulation, obesity, and laminitis

Background

Metabolomics, the study of small‐molecule metabolites, has increased understanding of human metabolic diseases, but has not been used to study equine metabolic syndrome (EMS).

Objectives

(1) To examine the serum metabolome of Welsh Ponies with and without insulin dysregulation before and during an oral sugar test (OST). (2) To identify differences in metabolites in ponies with insulin dysregulation, obesity, or history of laminitis.

Animals

Twenty Welsh Ponies (mean ± SD; 13.8 ± 9.0 years) classified as non‐insulin dysregulated [CON] (n = 10, insulin < 30 mU/L) or insulin dysregulated [ID] (n = 10, insulin > 60 mU/L) at 75 minutes after administration of Karo syrup, obese (n = 6) or nonobese (n = 14), and history of laminitis (n = 9) or no history of laminitis (n = 11).

Methods

Case‐control study. Metabolomic analysis was performed on serum obtained at 0 minutes (baseline) and 75 minutes during the OST. Data were analyzed with multivariable mixed linear models with significance set at P ≤ .05.

Results

Metabolomic analysis of 646 metabolites (506 known) detected significant metabolite differences. At baseline, 55 metabolites (insulin response), 91 metabolites (obesity status), and 136 metabolites (laminitis history) were different. At 75 minutes, 51 metabolites (insulin response), 102 metabolites (obesity status), and 124 metabolites (laminitis history) were different.

Conclusions and Clinical Importance

Use of metabolomics could have diagnostic utility for early detection of EMS and provide new knowledge regarding the pathophysiology of metabolic perturbations associated with this condition that might lead to improved clinical management.

Paradigm shifts in understanding equine laminitis

Laminitis, one of the most debilitating conditions of all equids, is now known to be the result of several systemic disease entities. This finding, together with other recent developments in the field of laminitis research, have provoked a rethink of our clinical and research strategies for this condition. First, laminitis is now considered to be a clinical syndrome associated with systemic disease (endocrine disease, sepsis or systemic inflammatory response syndrome, SIRS) or altered weight bearing rather than being a discrete disease entity. Next, laminitis associated with endocrine disease (endocrinopathic laminitis) is now believed to be the predominant form in animals presenting (primarily) for lameness. Third, the designation of laminitis as a primary and severe basement membrane pathology now requires revision. Instead, current data now proposes a variable subclinical phase associated with gross changes in the hoof capsule, with stretching and elongation of the lamellar cells an early and key event in the pathophysiology. These findings have fuelled new mechanistic hypotheses and research directions that will be discussed, together with their implications for future clinical management.

Effect of age and dietary carbohydrate profiles on glucose and insulin dynamics in horses

BACKGROUND

Glucose and insulin dynamics may be different in adult and aged horses.

OBJECTIVES

To determine the effects of age and dietary carbohydrates on glucose and insulin dynamics in healthy horses.

STUDY DESIGN

Balanced Latin square with four isocaloric diets: CONTROL (hay plus restricted-starch-and-sugar fortified pellets), STARCH (control plus kibbled corn), FIBER (control plus unmolassed sugar beet pulp/soybean hull pellets) and SUGAR (control plus dextrose powder).

METHODS

A total of 16 healthy Thoroughbreds and Standardbreds divided into two age groups: ADULT (8.8 ± 2.9 years; n = 8) and AGED (20.6 ± 2.1 years; n = 8). Following dietary adaptation, horses underwent an insulin-modified frequently sampled intravenous glucose tolerance test (FSIGTT), modified oral sugar test (OST) and dietary meal challenge. Outcome variables included: insulin sensitivity (SI), disposition index (DI), glucose effectiveness (Sg) and acute insulin response to glucose (AIRg) from the FSIGTT; peak glucose, peak insulin, time to peak, area under the curve for glucose (AUCg) and insulin (AUCi) from the OST and dietary meal challenge. Data were analyzed using multivariable linear mixed regression modelling.

RESULTS

AIRg was higher in AGED (mean [95% confidence interval]; 582.0 [455.0-709.0]) vs. ADULT (358.0 [224.0-491.0]; P = 0.03). ADULT and AGED horses had a higher SI on STARCH (adult: 3.3 [2.3-4.2]; aged: 2.8 [1.9-3.7]) and SUGAR (adult: 3.4 [2.5-4.3]; aged: 4.0 [3.1-4.9]) diets compared with CONTROL (adult: 2.0 [1.1-2.9], P = 0.029 (starch), P = 0.009 (sugar); aged: 1.4 [0.5-2.2], P = 0.009 (starch), P < 0.001 (sugar)). Feeding a STARCH (adult: 21581.0 [15029.0-28133.0]; aged: 35205.0 [29194.0-41216.0]) or SUGAR (adult: 26050.0 [19885.0-32215.0]; aged: 25720.0 [19770.0-31670.0]) meal resulted in postprandial hyperinsulinaemia (AUCi).

MAIN LIMITATIONS

Study cohort contained two insulin-sensitive breeds and no insulin-resistant breeds.

CONCLUSIONS

Age and diet should be considered when evaluating glucose and insulin dynamics.

Claw disorders in dairy cattle - an unexpected association between energy metabolism and sole haemorrhages

The present study investigated whether changes of energy metabolism post-partum (pp) are associated with claw health. For this purpose, back-fat-thickness (BFT) was measured and blood samples were taken from 146 cows at four examination times. The serum levels of free fatty acids (FFA), ß-hydroxybutyrate (BHB) and glucose were measured. Furthermore, in the first week postpartum (pp) and at 8 weeks pp, a claw trimming was done and the presence and extent of sole haemorrhages (SH) was recorded. Animals with high BFT at calving and therefore high fat mobilisation and whose FFA and BHB levels in the first week pp exceeded the reference values had fewer pathological changes of the claws than thinner animals whose FFA and BHB levels stayed within reference ranges. The body condition before calving, represented in this study by BFT, plays an important role in non-infectious claw disorders. Poorer body condition was found to be associated with the SH that develop in the first 2 months of lactation.

Postprandial glucose, insulin, and glucagon-like peptide-1 responses of different equine breeds adapted to meals containing micronized maize

The enteroinsular axis is a complex system that includes the release of incretin hormones from the gut to promote the absorption and utilization of glucose after a meal. The insulinogenic effect of incretin hormones such as glucagon-like peptide-1 (GLP-1) remains poorly characterized in the horse. The aim of this study was to compare postprandial glucose, insulin, and GLP-1 responses of different equine breeds adapted to twice-daily meals containing micronized maize. Four Standardbred horses, 4 mixed-breed ponies, and 4 Andalusian cross horses in moderate BCS (5.5 ± 0.2 out of 9) were fed meals at 0800 and 1600 h each day. The meals contained micronized maize (mixed with soaked soybean hulls and lucerne chaff), with the amount of maize gradually increased over 12 wk to reach a final quantity of 1.7 g/kg BW (1.1 g/kg BW starch) in each meal. Animals had ad libitum access to the same hay throughout. After 12 wk of acclimation, serial blood samples were collected from all animals over a 14-h period to measure concentrations of glucose, insulin, and GLP-1, with meals fed immediately after the 0 and 8 h samples. Glucose area under the curve (AUC) values were similar between breed groups (P = 0.41); however, ponies and Andalusian horses exhibited significantly higher insulin AUC values after both meals compared with Standardbred horses (both P < 0.005). Postprandial GLP-1 AUC values were also significantly higher in ponies and Andalusian horses compared with Standardbred horses (breed × time interaction; P < 0.001). Correlation analysis demonstrated a strong positive association between concentrations of insulin and GLP-1 over time (rs = 0.752; P < 0.001). The increased insulin concentrations in ponies and Andalusian horses may partly reflect lower insulin sensitivity but could also be attributed to increased GLP-1 release. Given that hyperinsulinemia is a recognized risk factor for the development of laminitis in domestic equids, this study provides evidence that the enteroinsular axis warrants further investigation.

Endocrine, morphometric, and ultrasonographic characterization of neck adiposity in Andalusian horses

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 measured by RIA in 127 Andalusian horses. Neck circumferences (NC) were measured at 3 equidistant locations at 25%, 50%, and 75% of neck length (NC-25%, NC-50%, and NC-75%). At the same 3 locations, subcutaneous fat thickness (SFT-25%, SFT-50%, and SFT-75%) was measured ultrasonographically. In the population under study, a tendency to adiposity was confirmed by the elevated plasma leptin levels (7.47 ± 5.03 ng/mL). However, plasma insulin concentrations (4.05 ± 3.74 μIU/mL) were within normal range in most horses. Our results indicate that NC showed significant sexual dimorphism and did not correlate well with hormonal measurements. Ultrasonographic assessment of fat thickness at the base of the neck (SFT-75%) was significantly correlated with both plasma leptin and insulin and did not show differences between males and females. Thus, in the search for a single objective parameter which can be used in large populations, SFT-75% is a potential candidate and may be a meaningful parameter to predict EMS.

The effect of oral and intravenous dextrose on C-peptide secretion in ponies

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 fasted glucose-to-insulin ratios, and responses were compared between the 2 groups. C-peptide concentrations increased ( < 0.01) rapidly from fasted levels after both oral and i.v. dextrose, with similar area under the concentration-time curve (AUC) for both tests and a significant correlation with AUC. The AUC was similar in HI and NI ponies after i.v. dextrose, indicating similar pancreatic capacity for both groups. However, for oral dextrose, the AUC and the AUC were markedly higher ( < 0.05) in the HI ponies, indicating a greater secretion rate of these peptides. Slower insulin clearance might have also contributed to the larger AUC in HI ponies, but this hypothesis requires further investigation with specific measures of hepatic insulin clearance.

Equine metabolic syndrome

Laminitis is one of the most common and frustrating clinical presentations in equine practice. While the principles of treatment for laminitis have not changed for several decades, there have been some important paradigm shifts in our understanding of laminitis. Most importantly, it is essential to consider laminitis as a clinical sign of disease and not as a disease in its own right. Once this shift in thinking has occurred, it is logical to then question what disease caused the laminitis. More than 90 per cent of horses presented with laminitis as their primary clinical sign will have developed it as a consequence of endocrine disease; most commonly equine metabolic syndrome (EMS). Given the fact that many horses will have painful protracted and/or chronic recurrent disease, a good understanding of the predisposing factors and how to diagnose and manage them is crucial. Current evidence suggests that early diagnosis and effective management of EMS should be a key aim for practising veterinary surgeons to prevent the devastating consequences of laminitis. This review will focus on EMS, its diagnosis and management.

A review of equine sepsis

Sepsis is defined as an exaggerated, systemic inflammatory response to infection and is a common condition in horses. Systemic inflammatory response syndrome (SIRS) associated with bacterial infection is a hallmark of sepsis. Sepsis in neonatal foals is a common sequela of failure of passive transfer and, in addition to development of SIRS, may be characterised by bacteraemia, pneumonia, enterocolitis, omphalophlebitis, meningoencephalitis or arthritis. Sepsis in mature horses is most commonly observed secondary to gastrointestinal lesions that result in disrupted mucosa and bacterial translocation into circulation (endotoxaemia). Pleuropneumonia and metritis may also cause sepsis in mature horses. Diagnosis of sepsis is based on SIRS criteria as well as suspected or confirmed infection. Due to the relatively low sensitivity of microbial culture and the subjectivity of sepsis scoring, many sepsis biomarkers are being studied for their usefulness in diagnosis and prognostication of sepsis in horses. Treatment of sepsis requires an intensive care approach that includes antimicrobial drug administration, fluid resuscitation and pressure support, and treatment for inflammation, endotoxaemia and coagulopathy. Early recognition of sepsis and prompt antimicrobial drug treatment are critical for a successful outcome. Multiple organ dysfunction syndrome may occur in severe cases of sepsis, with common manifestations including laminitis and coagulopathies. Although prognosis for septic mature horses depends highly on the primary disease process, the overall survival rate in septic neonatal foals ranges from 26 to 86%, with most studies indicating a survival rate of 45-60%.

Effect of short-term hyperinsulinemia on the localization and expression of endothelin receptors A and B in lamellar tissue of the forelimbs of horses

OBJECTIVE

To determine the effect of short-term hyperinsulinemia on the localization and expression of endothelin receptor (ETR)-A and ETR-B in lamellar tissue of the forelimbs of horses.

SAMPLES

Distal portion of 15 cadaveric forelimbs from healthy adult horses (1 limb/horse) obtained immediately after slaughter at an abattoir.

PROCEDURES

Each forelimb was assigned to 1 of 3 treatment groups (perfused with autologous blood for 10 hours [control perfusion; n = 5], perfused with an insulin [142 ± 81 μU/mL] perfusate for 10 hours [insulinemic perfusion; 5], or not perfused [unperfused control; 5]). Immunohistochemical evaluation of lamellar tissue was performed to assess localization of ETR-A and ETR-B. Expression of ETR-A and ETR-B was measured semiquantitatively on a scale of 0 to 3 (0 = none, 1 = mild, 2 = moderate, and 3 = high-intensity staining) and quantitatively by means of gray value analysis with imaging software.

RESULTS

In all specimens, ETR-A and ETR-B were localized in endothelium, smooth muscle cells, axons, and keratinocytes. Quantitative expression of ETR-A in the midportion of the primary epidermal lamellae for the insulinemic perfusion group (149 ± 16) was lower than that for the control perfusion group (158 ± 15). Expression of ETR-B in the primary epidermal lamellae tips for the insulinemic perfusion group (140 ± 29) was higher than that for the control perfusion group (114 ± 8).

CONCLUSIONS AND CLINICAL RELEVANCE

Hyperinsulinemia caused significant changes in endothelin receptor expression, which suggested that ETR antagonists might be beneficial for treatment of laminitis in horses.

Pathology of Natural Cases of Equine Endocrinopathic Laminitis Associated With Hyperinsulinemia

Laminitis in equids is a clinical syndrome usually associated with systemic disease. Endocrinopathies recently have been recognized as the most common cause of laminitis, with hyperinsulinemia playing a key role. Descriptions of laminitis-associated lesions have been confusing due to the wide range of experimental models used, failure of adequate clinical documentation for naturally occurring cases, lack of separate analysis of inflammatory and endocrinopathic laminitis, and uncertainty regarding normal morphological variation of lamellae. In this study, lamellar morphology and pathology were described in 14 laminitic horses and ponies that had hyperinsulinemia (>20 mIU/l), with reference to 25 age- and breed-matched controls. The type and severity of lesions noted had no correlation with reported clinical duration and in at least some cases must have preceded it. Lesions were largely localized abaxially within the lamellar tissue and included apoptotic cell death, as well as lamellar fusion, hyperplasia, and partial replacement with aberrant keratin containing nucleated debris and proteinaceous lakes. The lesions resulted in irregular margins between the inner horn and the lamellar tissue. Acute separation originated from the abaxial region, with minimal associated inflammation. Axially, epidermal lamellar tapering was the most frequent morphological observation. The lesions in these chronic cases of laminitis were similar to those described in some inflammatory laminitis models and contained features seen in developmental phases of hyperinsulinemic models. These findings support the theory that repeated episodes of subclinical laminitis occur prior to clinical presentation. In addition, the pathology does not include extensive basement membrane failure seen in some inflammatory models.

Metabolic syndrome: is equine disease comparable to what we know in humans?

This review summarizes similarities and differences between the metabolic syndromes in humans and equines, concerning the anatomy, symptoms, and pathophysiological mechanisms. In particular, it discusses the structure and distribution of adipose tissue and its specific metabolic pathways. Furthermore, this article provides insights and focuses on issues concerning laminitis in horses and cardiovascular diseases in humans, as well as their overlap.