Effect of increased adiposity on insulin sensitivity and adipokine concentrations in horses and ponies fed a high fat diet, with or without a once daily high glycaemic meal

Development of a body condition index to estimate adiposity in ponies and horses from morphometric measurements

BACKGROUND

There is a high prevalence of obesity in ponies and pleasure horses. This may be associated with equine metabolic syndrome and an increased risk of laminitis. Body condition scoring (BCS) systems are widely used but are subjective and not very sensitive.

OBJECTIVES

To derive a body condition index (BCI), based on objective morphometric measurements, that correlates with % body fat.

STUDY DESIGN

Retrospective cohort study.

METHODS

Morphometric measurements were obtained from 21 ponies and horses in obese and moderate body condition. Percentage body fat was determined using the deuterium dilution method and the BCI was derived to give the optimal correlation with body fat, applying appropriate weightings. The index was then validated by assessing inter-observer variation and correlation with % body fat in a separate population of Welsh ponies; and finally, the correlation between BCI and BCS was evaluated in larger populations from studies undertaken in Australia, the United Kingdom and the United States.

RESULTS

The BCI correlated well with adiposity in the ponies and horses, giving a Pearson r value of 0.74 (P < 0.001); however, it was found to slightly overestimate the % body fat in leaner animals and underestimate in more obese animals. In field studies, the correlation between BCI and BCS varied particularly in Shetlands and miniature ponies, presumably due to differences in body shape.

MAIN LIMITATIONS

Further work may be required to adapt the BCI to a method that is more applicable for Shetlands and miniature ponies.

CONCLUSIONS

This BCI was able to provide an index of adiposity which compared favourably with condition scoring in terms of accuracy of estimating adiposity; and was more consistent and repeatable when used by inexperienced assessors. Therefore, this may be a useful tool for assessing adiposity; and may be more sensitive than condition scoring for tracking weight gain or weight loss in individual animals.

Factors associated with insulin responses to oral sugars in a mixed-breed cohort of ponies

BACKGROUND

Serum insulin concentration at 60 min (InsulinT60) during an oral sugar test (OST) indicates future laminitis risk and insulin dysregulation (ID). Associations between InsulinT60 and physical and owner-reported variables may help clinicians select individuals for ID testing. Associations between InsulinT60 and other metabolic markers may help elucidate ID pathophysiology.

OBJECTIVES

To describe associations between (A) season, physically-apparent and owner-reported factors and binary InsulinT60 interpretation (initial models) and (B) variables included in the initial models, other metabolic markers and continuous InsulinT60 (full models).

STUDY DESIGN

Prospective longitudinal.

METHODS

Non-laminitic ponies were examined and OSTs (0.3 mL/kg Karo syrup) performed every 6 months (autumn and spring) for ≤4 years. Factors associated with InsulinT60 were determined using mixed-effects models with physical, owner-reported, season and serum/plasma markers as fixed effects and pony and premises identifiers as random effects. Autumn and spring data were analysed separately for full models.

RESULTS

One thousand seven hundred and sixty-three OSTs from 367 ponies were included. High-risk InsulinT60 (>153 μIU/mL) was independently associated with (odds ratio, 95% confidence interval [CI]): age (1.36, 1.16-1.60), body condition score (BCS) (2.38, 1.21-4.69), and bulging supraorbital fatpads (7.25, 2.1-24.98). However, the initial models provided little explanatory power (Nakagawa R2  = 0.1-0.27). LoginsulinT60 was independently associated with (effect estimate, 95% CI): age (0.02, 0.01-0.04), Welsh/Welsh X breed (0.22, 0.05, 0.39), sex (gelding = -0.2, -0.34 to 0.06), BCS (0.16, 0.08-0.23), plasma adiponectin (-0.02, -0.02 to 0.01) and basal insulin (0.01, 0.01-0.01) in spring, and: age (0.03, 0.02-0.04), BCS (0.17, 0.08-0.26), bulging supraorbital fatpads (0.37, 0.2-0.54), turnout score (0.05, 0.02-0.09), plasma adiponectin (-0.01, -0.02 to 0.01), ACTH (per 10 pg/mL) (0.01, 0.00-0.01), triglycerides (0.28, 0.07-0.49) and InsulinT0 (0.01, 0.01-0.01) in autumn.

MAIN LIMITATIONS

Only non-laminitic ponies in one region were included.

CONCLUSIONS

Owner-reported and physically-apparent data were limited InsulinT60 predictors. InsulinT60 is a complex trait, independently associated with numerous variables, some with seasonal interactions.

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).

Occurrence of equine metabolic syndrome, clinical manifestations, and associated risk factors in Nigeria

Insulin dysregulation (ID) is central to the pathophysiology of equine metabolic syndrome (EMS), putting the horse at risk of laminitis. There is a paucity of information on the status of EMS in Nigeria. This study aimed to determine the occurrence of EMS, clinical manifestations, and associated risk factors in Nigeria. A cross-sectional study was carried out. Selected horses underwent an insulin 2-step response test to ascertain insulin dysregulation; a physical examination was carried out to diagnose laminitis and obesity. Risk factors were assessed using a questionnaire. The overall prevalence of EMS was 43.10%. Breed and sex were significantly associated with EMS, but age was not. Horses diagnosed with laminitis showed two signs of laminitis, namely, divergent hoof rings and widened white lines. Risk factors significantly associated with the prevalence of EMS were as follows: being a West African Barb horse (60.00%), being a stallion (67.86%), being a leisure horse (67.86%), only walking horses during exercise (68.00%), exercising horses once every 5 months (82.76%), tethering horses to a stake in the ground (67.86%), obesity (92.86%), and abnormal neck crest (83.33%). The risk of ID remains higher in obese horses. However, some of the horses with ID were not obese, indicating that there are other possible underlying causes of EMS.

Comparison of insulin sensitivity between healthy neonatal foals and horses using minimal model analysis

The equine neonate is considered to have impaired glucose tolerance due to delayed maturation of the pancreatic endocrine system. Few studies have investigated insulin sensitivity in newborn foals using dynamic testing methods. The objective of this study was to assess insulin sensitivity by comparing the insulin-modified frequently sampled intravenous glucose tolerance test (I-FSIGTT) between neonatal foals and adult horses. This study was performed on healthy neonatal foals (n = 12), 24 to 60 hours of age, and horses (n = 8), 3 to 14 years of age using dextrose (300 mg/kg IV) and insulin (0.02 IU/kg IV). Insulin sensitivity (SI), acute insulin response to glucose (AIRg), glucose effectiveness (Sg), and disposition index (DI) were calculated using minimal model analysis. Proxy measurements were calculated using fasting insulin and glucose concentrations. Nonparametric statistical methods were used for analysis and reported as median and interquartile range (IQR). SI was significantly higher in foals (18.3 L·min^-1· μIU^-1 [13.4–28.4]) compared to horses (0.9 L·min^-1· μIU^-1 [0.5–1.1]); (p < 0.0001). DI was higher in foals (12 × 10³ [8 × 10³−14 × 10³]) compared to horses (4 × 10² [2 × 10²−7 × 10²]); (p < 0.0001). AIRg and Sg were not different between foals and horses. The modified insulin to glucose ratio (MIRG) was lower in foals (1.72 μIU_insulin²/10·L·mg_glucose [1.43–2.68]) compared to horses (3.91 μIU _insulin²/10·L·mg_glucose [2.57–7.89]); (p = 0.009). The homeostasis model assessment of beta cell function (HOMA-BC%) was higher in horses (78.4% [43–116]) compared to foals (23.2% [17.8–42.2]); (p = 0.0096). Our results suggest that healthy neonatal foals are insulin sensitive in the first days of life, which contradicts current literature regarding the equine neonate. Newborn foals may be more insulin sensitive immediately after birth as an evolutionary adaptation to conserve energy during the transition to extrauterine life.

Effect of Dose and Fasting on Oral Sugar Test Responses in Insulin Dysregulated Horses

The oral sugar test (OST) is frequently used to identify insulin dysregulated (ID) equines. The effect of fasting and varying sugar dose for the OST has been investigated in the pony but little work has been done in the horse. This study aimed to investigate (1) an OST response with access to forage continued until the time of the OST or prevented for 3 hours prior to the OST and (2) responses of ID and non-insulin dysregulated (NID) horses to two different OST doses. Twenty-one mixed-breed horses (14.8 ± 3.2 years; 574.3 ± 83.3 kg) were used in two randomized crossover studies. Seven ID and seven NID horses were used in study A, and eight ID and eight NID in study B. Study A horses underwent an OST (0.15 mL/kg BW) either after a fast (FA) or directly off pasture (FE). Study B horses received either a low (LD; 0.15 mL/kg BW) or high dose (HD; 0.45 mL/kg BW) OST on one occasion each. Blood was collected at basal (T0), and post-60 minute (T60) for later determination of insulin (RIA). Data were analyzed via ANOVA with repeated measures. ID horses had significantly (P < 0.05) greater insulin responses than NID for all OSTs. There was no statistical difference between LD versus HD mean insulin concentrations (T0, T60, delta insulin) for either ID or NID horses. ID had higher T0 (P < 0.01) for FE compared to FA; however, FE and FA did not significantly affect T60 or delta insulins (DI) concentrations.

"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.

Changes Associated with the Peri-Ovulatory Period, Age and Pregnancy in ACTH, Cortisol, Glucose and Insulin Concentrations in Mares

Simple Summary

The reproductive cycle of mares is associated with many hormonal changes, but the effects of this cycle and pregnancy on adrenocorticotropic hormone and insulin concentrations are poorly described, which could limit our ability to diagnose pituitary pars intermedia dysfunction and insulin dysregulation. In this study, healthy mares are followed through their reproductive cycle during the physiologic breeding season, and adrenocorticotropic hormone, cortisol, glucose and insulin concentrations are measured to determine the effects of age, pregnancy and the reproductive cycle on analyte concentrations. No significant effect of age, the reproductive cycle or pregnancy is detected on the cortisol, glucose or insulin concentrations; however, adrenocorticotropic hormone concentrations are significantly increased throughout the peri-ovulatory period and during pregnancy. Therefore, knowledge of a mare’s reproductive cycle might be beneficial when interpreting adrenocorticotropic hormone concentrations.

Abstract

Although there are many hormonal changes associated with reproduction, the effects of ovulation and early pregnancy on adrenocorticotropic hormone (ACTH) and insulin concentrations are poorly described. We hypothesise that both ovulation and early pregnancy will alter ACTH and insulin concentrations in healthy mares. Eighteen mares showing no clinical signs suggestive of, or laboratory findings consistent with, pituitary pars intermedia dysfunction PPID and insulin dysregulation (ID) are enrolled. ACTH, cortisol, insulin and glucose concentrations are measured over their peri-ovulatory period, as determined via ultrasounds and progesterone concentrations. The mares are grouped by age and gestation status, and a two-way repeated-measures ANOVA is used to determine the effects of age and early pregnancy, along with the peri-ovulatory period, on analyte concentrations. No significant effect of age, ovulation or early pregnancy is detected on the mares’ cortisol, insulin or glucose concentrations; however, there is a significant effect of early pregnancy and ovulation on ACTH concentrations (p = 0.04 and p = 0.04 respectively). ACTH concentrations change around ovulation and with early pregnancy. Therefore, knowledge of a mare’s reproductive status might be beneficial when interpreting ACTH concentrations.

Circannual variation in plasma adrenocorticotropic hormone concentrations and dexamethasone suppression test results in Standardbred horses, Andalusian horses and mixed-breed ponies

OBJECTIVE

To compare circannual plasma concentrations of adrenocorticotropic hormone (ACTH) and seasonal dexamethasone suppression test (DST) results between three different equine breed groups.

METHODS

Six Standardbred horses, six Andalusian horses and six mixed-breed ponies were followed over a 1-year period, during which time groups were managed identically. Blood samples were collected monthly (around the autumn equinox) or in every second month (other times of the year) for the determination of plasma ACTH concentrations using a chemiluminescent immunoassay. Overnight DSTs were performed quarterly, with suppression of plasma cortisol to below 27 nmol/L at 19 h considered a normal result.

RESULTS

Seasonal variation in plasma ACTH concentrations was present among all breed groups with, as expected, higher levels detected around the autumn equinox, from February to April (P < 0.001). Plasma ACTH concentrations were different between breed groups in March, with higher levels in Andalusians compared with Standardbreds (P = 0.048) and in ponies compared with Standardbreds (P = 0.010). Suppression of cortisol during the DST was normal for all animals in winter, spring and summer, but five Andalusians and three ponies returned abnormally high results in autumn, compared with zero Standardbreds.

CONCLUSION

Higher plasma ACTH concentrations and more false-positive DST results were obtained during autumn in ponies and Andalusian horses when compared with Standardbred horses. Potential differences between breeds should be considered when interpreting test results for horses and ponies that are evaluated for pituitary pars intermedia dysfunction. Further work is recommended to establish population-based reference intervals and clinical cut-off values for ACTH in different equine breeds.

Effects of equine metabolic syndrome on inflammation and acute-phase markers in horses

Obesity and metabolic disorders are associated with systemic low-grade chronic inflammation, both in humans and animals. The aim of the study is to assess the effects of obesity and hyperinsulinemia on individual components of the acute-phase reaction in equine metabolic syndrome (EMS) horses. Eight mixed-breed EMS and six control, age-matched horses of both sexes were included in the study. Animals were classified as EMS or control based on the assessment of BCS, cresty neck score, and basal insulin >50 μU/mL and/or insulin responses to the oral sugar test (OST) >60 μU/mL. Peripheral venous blood was collected. The expression of proinflammatory cytokines, the concentration of circulating cytokines, and acute-phase proteins (serum amyloid A, C-reactive protein, haptoglobin, activin A, and procalcitonin) were measured. The data were analyzed using the Mann-Whitney test, whereas correlations were examined using Spearman's correlation coefficient. The tests were statistically significant if P ≤ 0.05. There were no differences in cytokine gene expression, circulating cytokine concentrations, or concentrations of acute-phase proteins between the EMS and the control groups. There was a strong correlation between the basal concentration of insulin and the serum concentrations of IL-6 (r = 0.71, P < 0.05). Activin A was positively correlated with post-OST insulin concentrations (r = 0.707, P = 0.05), indicating that this marker of inflammation could warrant further investigation in horses with EMS.

Preliminary analysis of the FAM174A gene suggests it lacks a strong association with equine metabolic syndrome in ponies

Equine metabolic syndrome (EMS) describes a group of risk factors, including obesity and insulin dysregulation (hyperinsulinemia and/or insulin resistance), that can lead to the development of the debilitating hoof disease laminitis. Although the underlying mechanisms of EMS are not fully understood, a genetic component has been reported, and an 11 guanine polymorphism located at the FAM174A gene has been identified as a risk locus for the syndrome in Arabian horses. To examine associations between the FAM174A risk allele and the clinical signs of EMS, the allele was examined in an Australian cohort of ponies (n = 20) with known metabolic status. The 11 guanine polymorphism was identified in only 3 of 13 ponies with EMS, and no significant association could be made between the risk loci and morphometric measurements associated with obesity (BCS [P = 0.21], cresty neck score [P = 0.58], basal triglyceride concentration [P = 0.85], and adiponectin concentration [P = 0.48]), or insulin dysregulation (insulin dysregulation status [P = 0.35] and serum insulin concentration during an oral glucose test [P = 0.44]). These results suggest that the FAM174A 11 guanine homopolymer allele is unlikely to be a singular key gene polymorphism associated with EMS in ponies. However, due to the small number of ponies identified with the polymorphism, further study of the FAM174A risk allele in a larger cohort of horses and ponies of uniform breed would be useful.

Weight loss is linearly associated with a reduction of the insulin response to an oral glucose test in Icelandic horses

BACKGROUND

Insulin dysregulation (ID) goes along with lasting or transient hyperinsulinemia able to trigger equine laminitis, a painful and crippling foot condition. Promoting weight loss through dietary changes and physical activity is currently the main option to prevent this disease. This study aimed at describing the relationship between weight variations and the level of ID as determined by oral glucose tests (OGT). Therefore, the insulin response of 19 Icelandic horses to repeated OGTs was retrospectively analysed considering the variations in their body weight.

RESULTS

There was a strong linear relationship between variations in body weight and variations in the total insulin response to OGT as approximated by the area under the curve of insulin (p < 0.001). As indicated by a weighted least squares model, the insulin response decreased by 22% for 5% weight loss on average. However some horses did not respond to weight loss with a reduction of their insulin response to OGT. Additionally, a high correlation between 120 min serum insulin concentration and total insulin response was observed (r = 0.96, p < 0.001).

CONCLUSIONS

The results corroborate that weight loss is effective against ID and allow for a better quantification of the expected improvement of the insulin response after weight loss. However, it is unclear why some horses did not respond as expected. The high correlation between the 120 min insulin concentration and total insulin response suggests that insulin status can be accurately determined and monitored with only few samples in a practical setting.

Effect of long-term overfeeding of a high-energy diet on glucose tolerance in Shetland pony mares

Background

Overfeeding is associated with obesity and insulin dysregulation (ID), which are both risk factors for equine metabolic syndrome. How chronic overfeeding affects development of these factors is poorly understood.

Objectives

To examine the influence of long‐term high‐energy diet provision on body condition and ID.

Animals

Eleven Shetland pony mares.

Methods

In a 3‐phase study, the high‐energy group (n = 7) was fed 200% of net energy (NE) requirements (hay; concentrate: 36% sugar and starch, 13% fat) for 24 weeks, followed by 17 weeks hay‐only feeding before resuming the high‐energy diet (n = 4) for an additional 29 weeks. Mares were weighed weekly. Oral glucose tolerance tests were performed 3 to 4 times per dietary period. Results were compared with those of a control group (phase 1, n = 4; phases 2 and 3, n = 6) that received 100% NE requirements, using a general linear mixed model with post hoc Bonferroni testing.

Results

The mean body weight of the high‐energy group increased by 27% per high‐energy feeding period. During both feeding periods, area under the curve (AUC) for plasma glucose concentration decreased (P < .01), whereas AUC for plasma insulin concentration increased. Mean basal plasma glucose concentration and peak plasma insulin concentrations were higher (P < .05) in the high‐energy group than in the control group.

Conclusion and Clinical Importance

Feeding a high‐energy diet to healthy nonobese Shetland pony mares led to more efficient glucose metabolism within 5 weeks, followed by significant hyperinsulinemia and obesity. Hyperinsulinemic status was reversed during 17 weeks of hay‐only feeding, regardless of body condition, but returned rapidly after restarting the high‐energy diet.

Higher body mass index may increase the risk for the development of incisional complications in horses following emergency ventral midline celiotomy

BACKGROUND

Obesity is common in the equine population and it has been associated with increased surgical morbidity and mortality in humans. The effect of increased body mass index (BMI) on the incidence of surgical site infections has not been investigated in horses.

OBJECTIVES

To determine whether horses with increased body fat, as estimated by BMI, are more likely to develop post-operative complications, particularly incisional complications, following emergency ventral midline celiotomy.

STUDY DESIGN

Retrospective, multi-institutional clinical study.

METHODS

Medical records of horses >2 years old presenting with colic that underwent ventral midline celiotomy between January 2010 and September 2018 with follow-up of a minimum of 30 post-operative days were reviewed. Extracted data included signalment, operative details and outcome. BMI was calculated by dividing the patient's weight (kg) by the withers height squared (m² ).

RESULTS

In all, 287 horses fit inclusion criteria. Incisional complication prevalence was 23.7%. Horses with incisional complications had a higher BMI (median 203.6 kg/m² , IQR = 191.5-217.4) compared with those without (median 199.1 kg/m² , IQR = 184.7-210.2) (P = .03). Multi-variable analysis of the effects of age, sex, breed and presence of metabolic disease on the association between BMI and risk of incisional complications, identified a tendency towards increased risk with a higher BMI, but statistical significance decreased to P = .07. Breed had an association with BMI (P < .01), but not with incisional complication risk.

MAIN LIMITATIONS

BMI as an estimate of body fat has limitations. Retrospective studies with reliance on owners reporting data and complete medical records is imperfect. When the data were subjected to multi-variable analysis, the trend towards an increased incidence of incisional complications in horses with higher BMI persisted but it was not statistically significant.

CONCLUSION

Higher BMI may increase the risk for the development of incisional complications in horses following emergency ventral midline celiotomy.

Equine metabolic syndrome: evolution of understanding over two decades: a personal perspective

There has been a marked increase in the incidence of equine obesity globally, especially in countries where there has been a shift away from the horse having an economically essential working role. This change in its core role, plus the increasing numbers of individual horse owners without access to traditional knowledge of animal and land management, have helped fuel this equine obesity ‘epidemic’. Other important potential contributory factors include increased availability of good grazing and/or forage, as well as supplementary feeds. Obesity now presents a major welfare issue for horses and ponies, not only because of the direct weight-associated effects, but also due to the increased risk it poses for certain clinical conditions, in particular laminitis. For many owners and veterinarians, obesity and the equine metabolic syndrome are synonymous, but this is not necessarily the case. Furthermore, as we understand more about this syndrome and the causes of endocrinopathic laminitis, the emphasis has shifted from tissue or peripheral insulin resistance to insulin dysregulation. The present paper outlines how our knowledge of equine metabolic syndrome arose and continues to develop, as well as the authors’ personal involvement in some of these advances.

Genome-Wide Association Analyses of Equine Metabolic Syndrome Phenotypes in Welsh Ponies and Morgan Horses

Equine metabolic syndrome (EMS) is a complex trait for which few genetic studies have been published. Our study objectives were to perform within breed genome-wide association analyses (GWA) to identify associated loci in two high-risk breeds, coupled with meta-analysis to identify shared and unique loci between breeds. GWA for 12 EMS traits identified 303 and 142 associated genomic regions in 264 Welsh ponies and 286 Morgan horses, respectively. Meta-analysis demonstrated that 65 GWA regions were shared across breeds. Region boundaries were defined based on a fixed-size or the breakdown of linkage disequilibrium, and prioritized if they were: shared between breeds or across traits (high priority), identified in a single GWA cohort (medium priority), or shared across traits with no SNPs reaching genome-wide significance (low priority), resulting in 56 high, 26 medium, and seven low priority regions including 1853 candidate genes in the Welsh ponies; and 39 high, eight medium, and nine low priority regions including 1167 candidate genes in the Morgans. The prioritized regions contained protein-coding genes which were functionally enriched for pathways associated with inflammation, glucose metabolism, or lipid metabolism. These data demonstrate that EMS is a polygenic trait with breed-specific risk alleles as well as those shared across breeds.

Ultrasonographic measures of body fatness and their relationship with plasma levels and adipose tissue expression of four adipokines in Welsh pony mares

Obesity is responsible for metabolic dysregulations that alter fertility and induce pathologies. The objectives of the present study were to validate a reliable method for the evaluation of body fatness in mares and to associate the body fat estimation data to metabolic changes, including adipokines at the plasma and adipose tissue levels. To reach this purpose, animals were subjected to two extreme breeding conditions to study the variation of morphological, ultrasound, and physiological parameters. Twenty Welsh mares were followed up monthly from April to October before and after animals were moved outdoors to grasslands. Body weight (BW), body length (BL), height at the withers (HW), thoracic perimeter (TP), 5-point body condition score (BCS), and subcutaneous fat thickness (SFT) at the level of the shoulder, the lumbar region, and the rump, measured by ultrasonography, and plasma and adipose tissue metabolic indicators were assessed in parallel. Statistical analysis was performed using a linear mixed-effects model, whereas Pearson tests were used for the analysis of the correlations between the different parameters. Although mean BW did not increase significantly (P = 0.0940), TP (P = 0.0002) and BCS (P < 0.0001) increased during the study period. Ultrasonographic examination of subcutaneous adipose tissue showed an increase in SFT at the level of the shoulder (P < 0.0001), lumbar region (P < 0.0001), and rump (P < 0.0001). Plasma concentrations of nonesterified fatty acids (P < 0.0001), phospholipids (P < 0.0001), and cholesterol (P < 0.0001) increased significantly, whereas triglycerides (P < 0.0001) decreased significantly during the study period. Although both plasma concentrations and adipose tissue expression of leptin (P < 0.0001) and resistin (P < 0.0001) increased significantly, adiponectin (P < 0.0001) significantly decreased and visfatin remained unchanged (P = 0.8401). Expression of adipokine receptors studied showed the opposite pattern compared with their ligand. Ultrasonographic measurements of subcutaneous adipose tissue thickness at the shoulder, lumbar region, and rump are relevant indicators of fatness related with adipokine plasma concentrations and expression of adipokine-related receptors in adipose tissue, and particularly highlight seasonal effects.

Pharmacodynamic Effects of Pioglitazone on High Molecular Weight Adiponectin Concentrations and Insulin Response After Oral Sugar in Equids

Chronic insulin dysregulation is challenging to manage with pharmaceuticals in horses. Pioglitazone improves insulin sensitivity in humans, and the pharmacokinetics of pioglitazone have been evaluated in horses. The objectives of this study were to assess the pharmacodynamic effects of oral pioglitazone on morphometric parameters, hepatic enzyme activity and function, adipokines, and enteroinsular response to oral sugar. A prospective pilot study was performed using fifteen adult equids (8 ponies, 7 horses) to evaluate the effects of short-term pioglitazone administration (2 mg/kg PO q 24 hours, 28 days). Oral sugar tests (OST) were performed before and after treatment. Adipokines were measured at day 0, 14, and 28 of administration. Plasma drug concentrations were measured at day 14 and 28 of administration. The subjects were grouped into horses, ponies, and insulin dysregulated (ID) animals. Baseline values for all parameters were compared with values obtained at day 14 and 28 using one-way or two-way analysis of variance. Mild changes were noted in morphometric parameters and hepatic enzymes. No differences were found in leptin concentrations or the blood glucose response to the OST. Significant decreases were found in the insulin response to OST at 90 and 120 minutes time points and the area under the curve after pioglitazone treatment in the pony and ID groups. High-molecular-weight (HMW) adiponectin concentrations were significantly increased in all groups after pioglitazone treatment. Decreased insulin concentrations in response to oral sugar and increased HMW adiponectin concentrations indicate positive effects of pioglitazone for treatment of metabolic derangements in equine metabolic syndrome, which warrant future clinical study.

Evaluation of combined testing to simultaneously diagnose pituitary pars intermedia dysfunction and insulin dysregulation in horses

Background

The thyrotropin‐releasing hormone (TRH) stimulation test and the 2‐step insulin sensitivity test are commonly used methods to diagnose, respectively, pituitary pars intermedia dysfunction (PPID) and insulin dysregulation (ID).

Objectives

To investigate the diagnostic value of combining the TRH stimulation test and the 2‐step insulin sensitivity test to diagnose PPID and ID simultaneously.

Animals

Twenty‐seven adult horses, 10 control horses without PPID or ID, 5 horses with PPID only, 5 horses with ID only, and 7 horses with PPID and ID.

Methods

Randomized prospective study. Horses underwent a TRH stimulation test alone, a 2‐step insulin sensitivity test alone, and combined testing with simultaneous TRH and insulin injection in the same syringe. Data were compared by 2‐way repeated measures analysis of variance and 2 1‐sided tests to demonstrate equivalence. Bland‐Altman plots were generated to visualize agreement between combined and independent testing.

Results

The effect of combined testing on plasma adrenocorticotropic hormone, blood glucose concentration, or percentage decrease in blood glucose concentration was not significantly different from the effect obtained with independent testing. One control horse appeared falsely positive for PPID, 2 PPID‐only horses appeared falsely positive for ID, and 1 PPID and ID horse appeared falsely negative for ID when tests were performed simultaneously. Bland‐Altman plots supported the agreement between combined and independent testing.

Conclusions and Clinical Importance

Combining the TRH stimulation test and the 2‐step insulin sensitivity test appears to be a useful diagnostic tool for equine practitioners in the field, allowing testing of a horse for both PPID and ID simultaneously.

Glucose and Insulin Responses to an Intravenous Glucose Load in Thoroughbred and Paso Fino Horses

Certain breeds of horses may be genetically predisposed to developing insulin dysregulation, which is a risk factor for development of endocrinopathic laminitis in horses. This study was performed to test the hypotheses that Paso Fino horses exhibit evidence of insulin dysregulation compared with Thoroughbred horses and that obesity exaggerates the insulin dysregulation. Intravenous glucose tolerance tests were performed in 14 moderate-weight Thoroughbreds, 12 moderate-weight Paso Finos, and 12 overweight Paso Finos. Moderate Paso Finos had greater baseline serum insulin concentrations, area under the insulin concentration curve, peak insulin, insulin-to-glucose ratio, area under the insulin to glucose curve, and modified glucose-to-insulin ratio compared with moderate Thoroughbreds. The reciprocal inverse square of basal insulin (RISQI) and glucose-to-insulin ratio were significantly lower in moderate Paso Finos compared with moderate Thoroughbreds. Overweight Paso Finos had greater baseline insulin concentrations, area under the insulin concentration curve, time to peak insulin, baseline plasma glucose concentration, insulin-to-glucose ratio, and area under the insulin to glucose curve compared with moderate Paso Finos. The RISQI and glucose-to-insulin ratio were significantly lower in overweight Paso Finos compared with moderate Paso Finos. In conclusion, moderate-weight Paso Finos had higher baseline serum insulin concentrations and an excessive hyperinsulinemic response to an intravenous glucose load when compared with moderate-weight Thoroughbreds. Overweight Paso Finos had even greater baseline insulin concentrations and hyperinsulinemic responses to glucose compared with moderate Paso Finos, as well as greater baseline plasma glucose concentrations. Paso Finos exhibit insulin dysregulation compared with Thoroughbreds.

The cresty neck score is an independent predictor of insulin dysregulation in ponies

Generalized obesity, regional adiposity, hyperinsulinemia and hypertriglyceridemia are all potential indicators of equine metabolic syndrome (EMS). This study aimed to assess the relationship between morphometric measurements of body condition and metabolic hormone concentrations in ponies, with and without a neck crest or generalised obesity. Twenty-six ponies were assigned a body condition score (BCS) and cresty neck score (CNS). Height, girth, and neck measurements were taken. An oral glucose test (OGT; 0.75g dextrose/kg BW) was performed and blood samples collected prior to and 2 hours post dosing. Basal blood samples were analysed for blood glucose, serum insulin, triglyceride and leptin, and plasma HMW adiponectin concentrations. Post-prandial samples were analysed for serum insulin concentration. The ponies were grouped as having a) a normal to fleshy body status (BCS ≤7 and CNS ≤2; n = 10); b) having a high CNS, but without generalised obesity (BCS ≤7 and CNS ≥3; n = 11), or c) being obese (BCS ≥8 and CNS ≥1; n = 5). Responses to the OGT indicated that both normal and insulin-dysregulated ponies were included in the cohort. Post-prandial serum insulin was positively associated with CNS (P<0.035) and ponies with a CNS ≥ 3 had 5 times greater odds of being insulin-dysregulated. The high CNS group had a greater insulin response to the OGT than those in the normal/fleshy group (P = 0.006), whereas obese ponies did not differ from the other two groups. Basal HMW adiponectin was negatively correlated with post-prandial insulin concentrations (r = -0.5, P = 0.009), as well as being decreased in the group with a high CNS, compared to the obese group (P = 0.05). Cresty neck score was more predictive of insulin dysregulation than BCS, and this may be relevant to the diagnosis of EMS. Adiponectin may also be a measure of insulin dysregulation that is independent of body condition.

Novel lipoprotein density profiling in laminitic, obese, and healthy horses

Lipoproteins are water-miscible macromolecules enabling the transport of lipids in blood. In humans, altered proportions of lipoproteins are used to detect and classify metabolic diseases. Obesity and obesity-related comorbidities are common in horses. The pathophysiology of obesity is poorly understood and likely multifactorial. Development of new diagnostic tests to identify horses at risk of developing obesity to implement preventative measures is critical; however, a necessary first step to accomplish this goal is to improve our understanding of the pathophysiology of disease. Thus, the objective of this study was to characterize and compare lipoprotein profiles of horses with normal and excess body conditions, with and without laminitis using a novel method of continuous lipoprotein density profiling (CLPDP). Comparisons were made between 4 groups of horses: (1) laminitic, obese horses (n = 66); (2) laminitic, nonobese horses (n = 35); (3) nonlaminitic, obese horses (n = 41); and (4) nonlaminitic, nonobese horses (n = 95). Lipoprotein profiling, including evaluation of triglyceride-rich lipoprotein (TRL), low-density lipoproteins (LDLs), and high-density lipoproteins (HDLs) was performed using CLPDP, and all 4 groups were compared. A significant difference was observed among groups for the subfractions TRL, LDL1, LDL2, HDL2b, HDL2a, HDL3a, HDL3b, HDL3c, and total HDL. This is the first known description of CLPDP to characterize equine lipid profiles and holds promise as a useful method for lipid characterization of horses.

Association of sustained supraphysiologic hyperinsulinemia and inflammatory signaling within the digital lamellae in light-breed horses

Background

Hyperinsulinemia is associated with equine laminitis, and digital lamellar inflammation in equine metabolic syndrome‐associated laminitis (EMSAL) is modest when compared with sepsis‐associated laminitis.

Objectives

To characterize digital lamellar inflammation in horses in a euglycemic‐hyperinsulinemic clamp (EHC) model of laminitis.

Animals

Sixteen healthy adult Standardbred horses.

Methods

Prospective experimental study. Horses underwent EHC or saline infusion (CON) for 48 hours or until the onset of Obel grade 1 laminitis. Horses were euthanized, and digital lamellar tissue was collected and analyzed via polymerase chain reaction (pro‐inflammatory cytokine and chemokine genes—CXCL1, CXCL6, CXCL8, IL‐6, MCP‐1, MCP‐2, IL‐1β, IL11, cyclooxygenases 1 and 2, tumor necrosis factor alpha [TNF‐α], E‐selectin, and ICAM‐1), immunoblotting (phosphorylated and total signal transducer and activator of transcription 1 [STAT1], STAT3, and p38MAPK), and immunohistochemistry (markers of leukocyte infiltration: CD163, MAC387).

Results

Lamellar mRNA concentrations of IL‐1β, IL‐6, IL‐11, COX‐2, and E‐selectin were increased; the concentration of COX‐1 was decreased; and concentrations of CXCL1, CXCL6, MCP‐1, MCP‐2, IL‐8, TNF‐α and ICAM‐1 were not significantly different in the EHC group compared to the CON group (P ≤ .003). Lamellar concentrations of phosphorylated STAT proteins (P‐STAT1 [S727], P‐STAT1 [Y701], P‐STAT3 [S727], and P‐STAT3 [Y705]) were increased in the EHC group compared to the CON group, with phosphorylated STAT3 localizing to nuclei of lamellar basal epithelial cells. There was no change in the lamellar concentration of P‐p38 MAPK (T180/Y182), but the concentration of total p38 MAPK was decreased in the EHC samples. There was no evidence of notable lamellar leukocyte emigration.

Conclusions and Clinical Importance

These results establish a role for lamellar inflammatory signaling under conditions associated with EMSAL.

Metabolic effects of antidiabetic drugs on adipocytes and adipokine expression

Several classes of antidiabetic agents have been developed that achieve their hypoglycemic outcomes via various molecular mechanisms. Adipose tissue is a major metabolic and energy-storing tissue and plays an important role in many metabolic pathways, including insulin signaling and insulin sensitivity. Adipose tissue monitors and regulates whole body homeostasis via production and release of potent proteins, such as adipokine and adiponectin, into the circulation. Therefore, any agent that can modulate adipocyte metabolism can, in turn, affect metabolic and glucose homeostatic pathways. Antidiabetic drugs are not only recognized primarily as hypoglycemic agents but may also alter adipose tissue itself, as well as adipocyte-derived adipokine expression and secretion. In the current review, we present the major evidence concerning routinely used antidiabetic agents on adipocyte metabolism and adipokine expression.

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.

Exploring relationships between body condition score, body fat, activity level and inflammatory biomarkers

Obesity is associated with inflammatory disorders in humans, including degenerative joint disease. While obesity is endemic in horses, its relationship to equine degenerative joint disease has not been explored. The current study sought to describe relationships between: body weight (BW), body condition score (BCS), lameness grade (AAEP), total body fat mass (kg; FM) and fat per cent (FP) [multifrequency bioelectrical impedance analysis (mfBIA)], age, gender, activity level (AL), synovial fluid (SF) and plasma (PL) PGE₂ and glycosaminoglycan (GAG) in horses. During this field investigation, the BCS (of nine) of 54 horses at multiple farms in southern Ontario, Canada, was determined. Horses were categorized as thin (BCS=3/9; n = 6), moderate (BCS=4 or 5/9; n = 18), overweight (BCS=6 or 7/9; n = 19) or obese (BCS=8 or 9/9; n = 11). Total fat mass (kg) and body fat% was measured using mfBIA, lameness was assessed (AAEP lameness scale) and synovial fluid was collected via aseptic arthrocentesis from the left intercarpal joint for assessment of inflammatory biomarkers (PGE₂ , GAG). Means were compared with a one-way ANOVA; correlation coefficients were calculated using a Spearman Rank Order Correlation to reveal correlations between variables. BCS was positively correlated with BW, FM, FP, AL and PL-PGE₂ . BW was also significantly positively correlated with PL-PGE₂ . It is concluded that BCS is significantly correlated with PL-PGE₂ , due in part to the combined effect of AL and body condition. Net inflammatory effects of body fat on risk for joint disease require further study.

Effects of age and diet on glucose and insulin dynamics in the horse

BACKGROUND

Age and diet may affect insulin sensitivity (SI) but these factors have received limited investigation in horses.

OBJECTIVES

To measure minimal model parameters during an insulin-modified frequently sampled intravenous glucose tolerance test (FSIGTT) after adaptation to a forage only diet (HAY) or forage supplemented with either starch/sugar-rich (SS) or oil/fibre-rich (FF) concentrate feeds; and to assess glucose and insulin responses to a standardised meal challenge (SMC, 4 g/kg BW of SS) after diet adaptation in adult and aged mares.

STUDY DESIGN

Latin square design with eight adult (5-12 years) and nine aged (>19 years) healthy mares.

METHODS

Diets were fed for 6 weeks, and the FSIGTT and SMC were performed after 31-32 and 41 days on each diet respectively. Data were analysed by a mixed ANOVA for repeated measures.

RESULTS

Acute insulin response to glucose (AIRg) was greater and SI was lower in aged horses, compared with adults, regardless of diet. Both AIRg and SI were greater in aged mares after adaptation to SS, as compared with HAY. Similar trends, although not statistically significant, were observed after adaptation to SS in adult mares. Peak insulin concentration and area under the insulin vs. time curve during the SMC were greater in aged than adult mares with all diets. Furthermore, area under the glucose vs. time curve was lower after adaptation to SS, when compared with other diets, in both groups.

MAIN LIMITATIONS

Transient weight loss occurred at the beginning of the study and only one sex was included. Incomplete ingestion of the SMC by four mares was another limitation.

CONCLUSIONS

Insulin responses to i.v. and enteral nonstructural carbohydrate challenge increase with age in healthy horses, regardless of diet fed.

Maternal obesity increases insulin resistance, low-grade inflammation and osteochondrosis lesions in foals and yearlings until 18 months of age

INTRODUCTION

Obesity is a growing concern in horses. The effects of maternal obesity on maternal metabolism and low-grade inflammation during pregnancy, as well as offspring growth, metabolism, low-grade inflammation, testicular maturation and osteochondrotic lesions until 18 months of age were investigated.

MATERIAL AND METHODS

Twenty-four mares were used and separated into two groups at insemination according to body condition score (BCS): Normal (N, n = 10, BCS ≤4) and Obese (O, n = 14, BCS ≥4.25). BCS and plasma glucose, insulin, triglyceride, urea, non-esterified fatty acid, serum amyloid A (SAA), leptin and adiponectin concentrations were monitored throughout gestation. At 300 days of gestation, a Frequently Sampled Intravenous Glucose Tolerance Test (FSIGT) was performed. After parturition, foals' weight and size were monitored until 18 months of age with plasma SAA, leptin, adiponectin, triiodothyronine (T3), thyroxine (T4) and cortisol concentrations measured at regular intervals. At 6, 12 and 18 months of age, FSIGT and osteoarticular examinations were performed. Males were gelded at one year and expression of genes involved in testicular maturation analysed by RT-qPCR.

RESULTS

Throughout the experiment, maternal BCS was higher in O versus N mares. During gestation, plasma urea and adiponectin were decreased and SAA and leptin increased in O versus N mares. O mares were also more insulin resistant than N mares with a higher glucose effectiveness. Postnatally, there was no difference in offspring growth between groups. Nevertheless, plasma SAA concentrations were increased in O versus N foals until 6 months, with O foals being consistently more insulin resistant with a higher glucose effectiveness. At 12 months of age, O foals were significantly more affected by osteochondrosis than N foals. All other parameters were not different between groups.

CONCLUSION

In conclusion, maternal obesity altered metabolism and increased low-grade inflammation in both dams and foals. The risk of developing osteochondrosis at 12 months of age was also higher in foals born to obese dams.

Incidence of laminitis and survey of dietary and management practices in pleasure horses and ponies in south-eastern Australia

OBJECTIVES

The aims of this study were to (1) report the incidence of laminitis among a population of horses and ponies attending Pony Clubs in Victoria, Australia, and (2) describe the dietary and management practices of the sample population.

METHODS

Researchers visited 10 Pony Clubs over a 10-month period. Horse and pony owners completed a questionnaire to provide information on management relating to diet and exercise. Owners were also asked to report their animal's history of laminitis, if any.

RESULTS

From a survey population of 233 horses and ponies, 15.0% of animals (35 individuals) were reported to have suffered from at least one episode of laminitis. Of the animals that had suffered from laminitis, more than half had experienced multiple episodes. The majority of previously laminitic horses and ponies (71.4%) had not experienced an episode of laminitis within the past 12 months; however, 14.2% had experienced an incident within the past month. The proportion of ponies affected by laminitis (31/142; 21.8%) was significantly higher (P < 0.001) than the proportion of horses affected by laminitis (4/91; 4.4%). The incidence of laminitis within the pony group sampled was 6.5 cases per 100 pony years, while the incidence in horses was 0.55 cases per 100 horse years.

CONCLUSION

This study provided information on the incidence of laminitis in the general population of pleasure horses and ponies in south-eastern Australia. It also provided an overview of dietary and management practices. Given the high incidence of animals that had been affected by laminitis (and the associated welfare implications), this study highlights the importance of owner education regarding appropriate feeding and management strategies to reduce the risk of laminitis.

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.

Repeatability of Oral Sugar Test Results, Glucagon-Like Peptide-1 Measurements, and Serum High-Molecular-Weight Adiponectin Concentrations in Horses

BACKGROUND

Repeatability of the oral sugar test (OST) has not been evaluated.

OBJECTIVES

We hypothesized that OST glucose, insulin, active (aGLP-1) and total (tGLP-1) glucagon-like peptide 1, and high-molecular-weight (HMW) adiponectin results would be repeatable.

ANIMALS

Fifty-three horses from a Tennessee research facility (n = 23) and private practice in Missouri (n = 30), including animals with medical histories of equine metabolic syndrome.

METHODS

Two OSTs were performed 7-14 days apart and plasma glucose and insulin concentrations were measured at 0, 60, and 75 minutes; a positive result was defined as detection of an insulin concentration >45 μU/mL at 60 or 75 minutes. Plasma aGLP-1 and serum tGLP-1 concentrations at 75 minutes and serum HMW adiponectin concentrations at 0 minute were measured in the Missouri group. Bland-Altman analyses were performed.

RESULTS

No adverse events were reported. Bland-Altman analysis indicated mean ± SD bias of 1.5 ± 14.8 μU/mL (95% confidence interval [CI], -27.6 to 30.5 μU/mL) and 1.2 ± 16.1 μU/mL (95% CI, -30.4 to 32.8 μU/mL) for insulin concentrations at 60 and 75 minutes, respectively. There was 91 and 83% agreement in test interpretation between test days for OST insulin results for all horses in the Tennessee and Missouri groups, respectively.

CONCLUSIONS AND CLINICAL IMPORTANCE

Repeatability of the OST was acceptable when values obtained from Bland-Altman analyses were evaluated, and there was good agreement in binary (negative/positive) test interpretation for insulin concentrations. However, wide 95% CIs were detected for insulin concentrations.

Effect of increased adiposity on insulin sensitivity and adipokine concentrations in different equine breeds adapted to cereal-rich or fat-rich meals

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 by gradually increasing the supplementary feeds to provide 200% of daily digestible energy requirements by Week 20. The CON group were fed a basal ration only and maintained moderate body condition. At Week 20, the CHO and FAT groups demonstrated significantly increased body condition score, bodyweight, total body fat mass and plasma leptin concentrations compared with the CON group (P <0.001). The CHO group had lower insulin sensitivity (SI; P <0.001) and higher acute insulin response to glucose (P = 0.002) than the CON group. In contrast, the FAT group was no different to the control group. Ponies and Andalusians had lower SI values compared with Standardbreds, regardless of diet group (P = 0.001). Adiponectin concentrations were similar between the FAT and CON groups, but were significantly lower in the CHO group (P = 0.010). The provision of cereal-rich meals appeared to be a more important determinant of insulin sensitivity than the induction of obesity per se. Whether hypoadiponectinaemia is a cause or consequence of insulin dysregulation warrants further investigation.