Effects of body weight reduction on blood adipokines and subcutaneous adipose tissue adipokine mRNA expression profiles in obese ponies

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.

Effect of Exercise Conditioning on Countering the Effects of Obesity and Insulin Resistance in Horses-A Review

Obesity is an important health concern in horses, along with humans and companion animals. Adipose tissue is an inflammatory organ that alters the insulin-signaling cascade, ultimately causing insulin dysregulation and impaired glucose metabolism. These disruptions can increase the risk of metabolic disease and laminitis in horses and may also impact energy metabolism during exercise. A single bout of exercise, along with chronic exercise conditioning, increases insulin sensitivity and glucose disposal via both contraction- and insulin-mediated glucose uptake pathways. Regular exercise also increases calorie expenditure, which can facilitate weight (as body fat) loss. This paper explores the metabolic pathways affected by adiposity, as well as discusses the impact of exercise on insulin metabolism in horses.

Variation in insulin response to oral sugar test in a cohort of horses throughout the year and evaluation of risk factors for insulin dysregulation

BACKGROUND

The oral sugar test (OST) is commonly used to diagnose insulin dysregulation (ID) and equine metabolic syndrome; however, possible seasonal changes in OST results have not been evaluated.

OBJECTIVE

To determine the possible variation in insulin response to OST throughout the year and risk factors associated with maximum insulin concentration (InsMax) and ID.

STUDY DESIGN

Prospective, longitudinal cohort study.

METHODS

The OST was performed on 29 Finnhorses every other month six times. Serum total adiponectin concentration and phenotypic variables related to obesity were also measured. Changes in InsMax, adiponectin, scale weight, body condition score, cresty neck score (CNS), and fasting glucose concentration were assessed. Risk factor analyses were performed on InsMax and ID status, and ID groups were compared with each other.

RESULTS

Fourteen horses were categorised with non-ID each time and 15 as having ID at least once during the follow-up period. The ID status of 12 horses varied throughout the year, but neither the insulin variables measured during the OST nor adiponectin expressed significant seasonal variation. Increasing age and CNS, and decreasing adiponectin were observed as risk factors for a high InsMax after OST. The risk of ID was higher in horses with no exercise compared to horses with exercise (OR 7.6, 95% CI 1.2-49.3, P = .03). Horses with ID had lower serum adiponectin concentrations, longer neck circumference and larger height than horses in the non-ID group.

MAIN LIMITATIONS

The environmental conditions (feeding, exercise) were not constant for all horses throughout the study and only one breed was used.

CONCLUSIONS

Neither OST results nor adiponectin varies with season; however, there were a substantial number of horses with variable ID status throughout the year, in which repeated OSTs may be beneficial. Lack of exercise was a risk factor for ID.

Morphometric, metabolic, and inflammatory markers across a cohort of client-owned horses and ponies on the insulin dysregulation spectrum

In human metabolic syndrome and type II diabetes, methylglyoxal (MG), D-lactate, and several cytokines have been recognized as biomarkers of important metabolic and inflammatory processes. Equine metabolic syndrome (EMS) shares many similarities with these human counterparts. The objectives of this cross-sectional study were to compare body condition score (BCS), cresty neck score (CNS), resting insulin, MG, D-lactate, L-lactate, tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and monocyte chemoattractant protein-1 (MCP-1) between horses with and without insulin dysregulation, as classified via combined glucose and insulin test (CGIT). 32 client-owned horses were included. History and morphometric data such as BCS and CNS were recorded. Subjects with abnormalities on physical examination or CBC, elevated ACTH or incomplete information were excluded. Baseline serum or plasma concentrations of biomarkers were tested via commercial ELISA or colorimetric assays. Characteristics of insulin dysregulated and insulin sensitive horses were compared by univariate analysis and forward logistic regression. 12 (38%) of the 32 horses were classified as insulin dysregulated. No significant difference between the 2 groups was found for age, BCS, baseline glucose, triglycerides, MG, D-lactate, L-lactate, TNF-α, IL-6, and MCP-1. Baseline insulin was significantly associated with insulin dysregulation in univariate analysis (P = 0.02), but not in the final model. Horses with CNS ≥ 3 had 11.3 times higher odds of having insulin dysregulation (OR 11.3, 95% C.I. 2.04 - 63.08, P = 0.006). In this population, horses with mild-moderate signs of EMS presented similar metabolic and inflammatory profiles to non-insulin dysregulated controls.

A Multiomic Approach to Investigate the Effects of a Weight Loss Program on the Intestinal Health of Overweight Horses

Obesity is endemic in human populations in the western society, and with mounting evidence that the intestinal ecological environment plays a major role in its pathogenesis, identification of therapies based on intestinal microbiota modulation are gaining attention. Obesity in companion animals is also a common clinical problem. We set out using a multidimensional approach, to determine the effectiveness and safety of a weight loss program for horses incorporating diet restriction and exercise. In addition, we aimed to investigate the effect of this program on the overall intestinal health of overweight sedentary horses. The investigation comprised of a randomized, controlled, 6-week study of 14 overweight sedentary horses and ponies who were blocked for age, gender, and breed (controls n = 7, treatment n = 7). The treatment group were fed a restricted diet (1.4% of body weight dry matter intake) and the control group a maintenance diet (2% of body weight as dry matter intake) over the study period. The treatment group were subjected to a prescribed exercise regime, while the control group were exercised to mimic foraging conditions. Several clinical measurements were taken at the start and end of the study, including morphological parameters, ultrasound measurements of subcutaneous fat, and blood pressure. Fecal microbiota analysis was performed using 16S rRNA gene sequence analysis, and fecal metabolome was analyzed using NMR spectroscopy, on samples taken at weeks 1, 3, and 6 of the study. All horses completed the study period successfully. However, two of the treatment group had to have modified exercise regimes. The treatment group showed significant weight loss (p < 0.00001) and an associated decrease in waste circumference (p < 0.0001) when compared with the control group. The alpha-diversity of the fecal microbiota in the treatment group showed a significant increase from the start to the end of the study period (p < 0.05); however, there was no significant difference between groups at any sampling point. There were significant changes (p < 0.05) in the metabolome in both groups between the start and end of the study, but not between groups at any sampling point. Finally, the resting blood pressure of all horses was significantly lower by the end of the study.

Metabogenomics reveals four candidate regions involved in the pathophysiology of Equine Metabolic Syndrome

An analogous condition to human metabolic syndrome, Equine Metabolic Syndrome (EMS) is defined by several clinical signs including obesity, hyperinsulinemia, and peripheral insulin dysregulation (ID). Affected horses may also exhibit hypertension, hyperlipemia and systemic inflammation. Measures of ID typically comprise the gold-standard for diagnosis in veterinary care. Yet, the dynamic nature of insulin homeostasis and complex procedures of typical assays make accurate quantification of ID and EMS challenging. This work aimed to investigate new strategies for identification of biochemical markers and correlated genes in EMS. To quantify EMS risk within this population, we utilized a composite score derived from nine common diagnostic variables. We applied a global liquid chromatography/mass spectroscopy approach (HPLC/MS) to whole plasma collected from 49 Arabian horses, resulting in 3392 high-confidence features and identification of putative metabolites in public databases. We performed a genome wide association analysis with genotypes from the 670k Affymetrix Equine SNP array utilizing EMS-correlated metabolites as phenotypes. We discovered four metabolite features significantly correlated with EMS score (P < 1.474 × 10^-5). GWAs for these features results (P = 6.787 × 10^-7, Bonferroni) identified four unique candidate regions (r² > 0.4) containing 63 genes. Significant genomic markers capture 43.52% of the variation in the original EMS score phenotype. The identified genomic loci provide insight into the pathways controlling variation in EMS and the origin of genetic predisposition to the condition. Rapid, feasible and accurate diagnostic tools derived from metabogenomics can be translated into measurable benefits in the timeline and quality of preventative management practices to preserve health in horses.

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.

Assessment of the FAM174A 11G allele as a risk allele for equine metabolic syndrome

An 11G nucleotide repeat in the 3' UTR of FAM174A was recently postulated as a risk allele with a dominant mode of inheritance for equine metabolic syndrome (EMS) and laminitis status in Arabian horses. The objective of this project was to evaluate this hypothesis in a large and diverse across-breed population. A total of 301 ponies, 292 Morgans, 64 Arabians, 49 Tennessee Walking Horses and 59 Quarter Horses were genotyped for six observed G repeat alleles in the FAM174A 3' UTR. Phenotype data included laminitis status, baseline insulin, glucose, non-esterified fatty acids, triglycerides, adiponectin, leptin, ACTH, insulin and glucose post oral sugar test, and two proxies for insulin resistance. The 11G allele frequencies were 18.8, 6.9, 1.8, 0.2 and 0.0% in the Arabians, Tennessee Walkers, ponies, Morgans and Quarter Horses respectively. Association analyses between FAM174A genotype and EMS phenotypes, and between allele count and EMS phenotypes, identified no statistically significant associations. When a dominant effect for the 11G allele was evaluated, a statistically significant association with adiponectin levels was identified in the ponies, and pairwise comparisons revealed that the estimated marginal means were higher in ponies with the 11G allele vs. alternative alleles (i.e. the allele had a protective effect). In conclusion, our data do not support the FAM174A 11G allele as a risk allele for EMS in our studied breeds.

Alterations of serum vitamin E and vitamin A concentrations of ponies and horses during experimentally induced obesity

Vitamin A, vitamin E and retinol-binding protein 4 (RBP4) are a focus of current obesity research in humans. The impact of body weight (BW) gain on fat-soluble vitamins and its associated parameters in equines has not been previously reported. Ten Shetland ponies and 9 Warmblood horses, all adult geldings, non-obese and healthy, were fed an excessive energy diet for 20 months to induce BW gain. Serum α-tocopherol (vitamin E), retinol (vitamin A), retinol-binding protein 4 (RBP4) and retinol/RBP4 ratio were analysed before BW gain induction and at six timepoints during the BW gaining period. The mean (±SD) % BW gain achieved during two years of excess energy intake was 29.9 ± 19.4% for ponies and 17 ± 6.74% for horses. Serum α-tocopherol increased significantly in ponies and horses during excess energy intake and circulating α-tocopherol levels correlated positively with α-tocopherol intake (r = .6; p < .001). Serum retinol concentrations showed variations during the study but without relation to intake. Serum RBP4 decreased at the end of the study. The retinol/RBP4 ratio increased with BW gain without differences between ponies and horses. In comparison with human research, the increase in the retinol/RBP4 ratio was unexpected and needs further elucidation.

Glucagon-like peptide-1, insulin-like growth factor-1, and adiponectin in insulin-dysregulated ponies: effects of feeding a high nonstructural carbohydrate diet and association with prospective laminitis

Endocrinopathic laminitis, related to equine metabolic syndrome and insulin dysregulation, causes marked pain and suffering in horses and represents a substantial cost to the horse industry. This study investigated the effect of feeding a diet high in nonstructural carbohydrates on concentrations of active glucagon-like peptide-1 (aGLP-1), total insulin-like growth factor-1 (IGF-1), and high-molecular-weight (HMW) adiponectin, in insulin-dysregulated ponies. Thirty-seven ponies were challenged with this diet for up to 18 d to induce hyperinsulinemia. Hormone concentrations were measured in selected samples on day 2 of the diet challenge period, over 4 h after feeding. Fourteen of the ponies developed mild laminitis induced by the diet challenge. Insulin and glucose responses to the diet have been reported previously. Feeding increased the concentrations of aGLP-1 (P < 0.05) and HMW adiponectin (P < 0.001), but there was no difference between the laminitic and nonlaminitic groups for either hormone. Concentrations of IGF-1 and insulin were inversely related, with IGF-1 being 32% lower in hyperinsulinemic/laminitic ponies compared with nonlaminitic ponies (P = < 0.05). These results indicate that unlike insulin and possibly IGF-1, concentrations of aGLP-1 and HMW adiponectin do not have a strong association with, or play a major role in, the pathogenesis of equine laminitis.

Adipose tissue dysfunction in obese horses with equine metabolic syndrome

BACKGROUND

Obesity is a common feature of equine metabolic syndrome (EMS). In other species, obese adipose tissue shows pathological features such as adipocyte hypertrophy, fibrosis, inflammation and impaired insulin signalling all of which contribute to whole body insulin dysregulation. Such adipose tissue dysfunction has not been investigated in horses.

OBJECTIVES

To determine if obese horses with EMS have adipose tissue dysfunction characterised by adipocyte hypertrophy, fibrosis, inflammation and altered insulin signalling.

STUDY DESIGN

Cross-sectional post-mortem study.

METHODS

Samples of peri-renal (visceral) and retroperitoneal adipose tissue were obtained at post-mortem from healthy horses (n = 9) and horses with EMS (n = 6). Samples were analysed to determine average adipocyte size, fibrotic content and expression of inflammatory and insulin signalling genes.

RESULTS

Horses with metabolic syndrome showed marked adipocyte hypertrophy and increased expression of adipokines (leptin) and inflammatory cytokines (TNFα, IL1β and CCL2) in both adipose tissue depots compared to healthy horses. There were no differences in fibrosis or expression of genes relating to insulin signalling between the groups.

MAIN LIMITATIONS

Cases used in this study had advanced EMS and may represent the end stage of the condition; the design of the study is such that we were unable to relate the identified adipose tissue dysfunction to whole body insulin dysregulation.

CONCLUSIONS

Horses with obesity and EMS have significant dysfunction of the peri-renal and retroperitoneal adipose tissue that may contribute to whole body insulin dysregulation.

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.

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.

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.

Impact of body weight gain on hepatic metabolism and hepatic inflammatory cytokines in comparison of Shetland pony geldings and Warmblood horse geldings

Background

Non-alcoholic fatty liver disease is known as determining part of human obesity. The impact of body weight (BW) gain on liver metabolism has not been extensively investigated yet.

Objectives

To investigate hepatic alterations caused by increasing BW in ponies and horses.

Animals

A total of 19 non-obese equines (10 Shetland ponies, geldings; nine Warmblood horses, geldings).

Methods

Animals received 200% of their metabolizable maintenance energy requirements for 2 years. Serum alkaline phosphatase, glutamate dehydrogenase (GLDH), aspartate aminotransferase (AST), and gamma-glutamyl transferase activities and bile acids were analyzed several times during 2 years of hypercaloric diet. Hepatic lipid content and hepatic levels of the interleukin (IL)-6, tumor necrosis factor α (TNFα), cluster of differentiation (CD) 68, IL-1β, lipoprotein lipase (LPL), fatty acid-binding protein 1, chemerin and nuclear factor-κB mRNAs were assessed at the start of the study and after 1 and 2 years of excess energy intake.

Results

The mean (±SD) BW gain recorded during 2 years of excess energy intake was 29.9 ± 19.4% for ponies and 17 ± 6.74% for horses. The hepatic lipid content was not profoundly affected by increasing BW. Levels of the IL-6, TNFα, CD68 and IL-1β mRNAs did not change during BW gain. Levels of the chemerin mRNA increased significantly in both breeds (ponies: P = 0.02; horses: P = 0.02) in response to BW gain. Significant differences in serum GLDH and AST activities, serum bile acid concentrations and hepatic levels of the LPL mRNA were observed between ponies and horses at the end of the study.

Conclusions

Chemerin might represent an interesting marker for future equine obesity research. Interestingly, steatosis caused by increasing BW may occur later in the development of obesity in equines than in humans. Additionally, the hepatic metabolism exhibits differences between ponies and horses, which may explain in part the greater susceptibility of ponies to obesity-associated metabolic dysregulations.

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.

Influence of dietary restriction and low-intensity exercise on weight loss and insulin sensitivity in obese equids

Background

The importance of including exercise with dietary modification for the management of obese equids is not clearly understood.

Objectives

To evaluate the effect of a practical low‐intensity exercise regimen, in addition to dietary restriction, on indices of insulin sensitivity (SI) and plasma adipokine concentrations in obese equids.

Animals

Twenty‐four obese (body condition score [BCS] ≥ 7/9) horses and ponies.

Methods

Over a 12‐week period, animals received either dietary restriction only (DIET) or dietary restriction plus low‐intensity exercise (DIET+EX). All animals were provided with a restricted ration of grass hay at 1.25% body weight (BW) on a dry matter basis, providing 82.5% estimated digestible energy requirements. The DIET+EX group undertook low‐intensity exercise 5 days per week on an automated horse walker. Before and after weight loss, total body fat mass (TBFM) was determined, indices of SI were calculated using minimal model analysis of a frequently sampled IV glucose tolerance test, and adipokines plus inflammatory biomarkers were measured using validated assays.

Results

Decreases in BCS, BW, and TBFM were similar between groups (all P > .05). After weight loss, animals in both groups had decreased basal insulin and leptin concentrations, and increased adiponectin concentrations (all P < .001). Furthermore, animals in the DIET+EX group had significantly improved SI and decreased serum amyloid A concentrations relative to animals in the DIET group (both P = .01).

Conclusions and Clinical Importance

Regular low‐intensity exercise provided additional health benefits compared with dietary restriction alone in this population of obese equids.

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.

Determination of lipid profiles in serum of obese ponies before and after weight reduction by using multi-one-dimensional thin-layer chromatography

Obesity is a key component of equine metabolic syndrome, which is highly associated with laminitis. Feed restriction and/or exercise are known to alleviate the detrimental effects of insulin resistance in obese ponies. However, little is known about changes in the serum lipid patterns due to weight reduction and its association with disease outcomes. Therefore, the lipid patterns in the serum of 14 mature ponies before and after a 14-week body weight reduction program (BWRP) were investigated by multi-one-dimensional thin-layer chromatography (MOD-TLC). Additionally, sensitivity to insulin (SI), body condition scores (BCS) and cresty neck scores (CNS) were measured. A BWRP resulted in a significant loss of body weight (P<0.001), which was associated with beneficial decreases in BCS and CNS (both, P<0.001). Serum lipid compositions revealed significantly increased free fatty acid (FFA), sphingomyelin (SM; both P<0.001), total cholesterol (C) and cholesterol ester (CE) (both P<0.01) and triacylglycerol (TG; P<0.05) densities. Improvement of SI after the BWRP was associated with increases in neutral lipids (C, CE and TG, all P<0.01), FFA and the phospholipid SM (both, P<0.001). The results show that a BWRP in obese ponies was effective and associated with changes in the concentrations of neutral lipids and the phospholipid SM, indicating that SM may play a role in insulin signaling pathways and thus in the pathogenesis of insulin resistance and the progression of metabolic syndrome in obese ponies.

Therapeutics for Equine Endocrine Disorders

Equine endocrine disease is commonly encountered by equine practitioners. Pituitary pars intermedia dysfunction (PPID) and equine metabolic syndrome (EMS) predominate. The most logical therapeutic approach in PPID uses dopamine agonists; pergolide mesylate is the most common. Bromocryptine and cabergoline are alternative drugs with similar actions. Drugs from other classes have a poor evidence basis, although cyproheptadine and trilostane might be considered. EMS requires management changes as the primary approach; reasonable justification for use of drugs such as levothyroxine and metformin may apply. Therapeutic options exist in rare cases of diabetes mellitus, diabetes insipidus, hyperthyroidism, and critical illness-related corticosteroid insufficiency.

Effects of diet-induced weight gain and turnout to pasture on insulin sensitivity in moderately insulin resistant horses

OBJECTIVE

To quantify insulin sensitivity and monitor glucose, insulin, and lipid concentrations in a group of moderately insulin-resistant horses during induction of obesity by use of a forage diet supplemented with fat and during subsequent turnout to pasture. ANIMALS 9 adult Standardbred mares (11 to 20 years old).

PROCEDURES

Weight gain of horses was induced during 22 weeks by use of a forage diet supplemented with fat fed in gradually increasing amounts, followed by feeding of that fat-supplemented diet at 2.5 times the daily maintenance requirements. Horses were then turned out to pasture. Insulin sensitivity was measured with the euglycemic hyperinsulinemic clamp method before and after weight gain and after 4 weeks at pasture. Body weight, body condition score, and cresty neck score as well as fasting and postprandial concentrations of plasma insulin, plasma glucose, serum triglyceride, and serum nonesterified fatty acids were measured during the study.

RESULTS

Body weight typically increased by 10%, and body condition score (scale, 1 to 9) increased by > 1.5 from the start to the end of the weight-gain period. There was no difference in insulin sensitivity or metabolic clearance rate of insulin during the weight-gain period. Four weeks at pasture generally improved insulin sensitivity and metabolic clearance rate of insulin by 54% and 32%, respectively, but there was no change in body weight or body condition score.

CONCLUSIONS AND CLINICAL RELEVANCE

Findings indicated that dietary composition played a more important role than did short-term weight gain on alterations in insulin sensitivity of horses.

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.

INVITED REVIEW: Evolution of meat animal growth research during the past 50 years: Adipose and muscle stem cells

If one were to compare today's animal growth research to research from a mere 50 yr ago, one would see programs with few similarities. The evolution of this research from whole-animal through cell-based and finally molecular and genomic studies has been enhanced by the identification, isolation, and in vitro evaluation of adipose- and muscle-derived stem cells. This paper will highlight the struggles and the milestones that make this evolving area of research what it is today. The contribution of adipose and muscle stem cell research to development and growth, tissue regeneration, and final carcass composition are reviewed.

Relationships among Body Condition, Insulin Resistance and Subcutaneous Adipose Tissue Gene Expression during the Grazing Season in Mares

Obesity and insulin resistance have been shown to be risk factors for laminitis in horses. The objective of the study was to determine the effect of changes in body condition during the grazing season on insulin resistance and the expression of genes associated with obesity and insulin resistance in subcutaneous adipose tissue (SAT). Sixteen Finnhorse mares were grazing either on cultivated high-yielding pasture (CG) or semi-natural grassland (NG) from the end of May to the beginning of September. Body measurements, intravenous glucose tolerance test (IVGTT), and neck and tailhead SAT gene expressions were measured in May and September. At the end of grazing, CG had higher median body condition score (7 vs. 5.4, interquartile range 0.25 vs. 0.43; P=0.05) and body weight (618 kg vs. 572 kg ± 10.21 (mean ± SEM); P=0.02), and larger waist circumference (P=0.03) than NG. Neck fat thickness was not different between treatments. However, tailhead fat thickness was smaller in CG compared to NG in May (P=0.04), but this difference disappeared in September. Greater basal and peak insulin concentrations, and faster glucose clearance rate (P=0.03) during IVGTT were observed in CG compared to NG in September. A greater decrease in plasma non-esterified fatty acids during IVGTT (P<0.05) was noticed in CG compared to NG after grazing. There was down-regulation of insulin receptor, retinol binding protein 4, leptin, and monocyte chemoattractant protein-1, and up-regulation of adiponectin (ADIPOQ), adiponectin receptor 1 and stearoyl-CoA desaturase (SCD) gene expressions in SAT of both groups during the grazing season (P<0.05). Positive correlations were observed between ADIPOQ and its receptors and between SCD and ADIPOQ in SAT (P<0.01). In conclusion, grazing on CG had a moderate effect on responses during IVGTT, but did not trigger insulin resistance. Significant temporal differences in gene expression profiles were observed during the grazing season.

Changes in oxidative stress in response to different levels of energy restriction in obese ponies

The present study evaluated the effect of different levels of energy restriction on metabolic parameters in obese ponies. Relative weight changes, markers of lipid metabolism and oxidant/antioxidant balance were monitored. A total of eighteen obese (body condition score ≥ 7/9) Shetland ponies were studied over a 23·5-week trial, which was divided into three periods. The first period involved a 4-week adaptation period in which each animal was fed 100% of their maintenance energy requirements needed to maintain a stable obese body weight (MERob). This was followed by a 16·5-week weight-loss period in which ponies were assigned to receive either 100% (control group, CONTROL), 80% (slow weight-loss (SLOW) group) or 60% (rapid weight-loss (RAPID) group) of their MERob. During the 3-week end-phase period, all ponies were again fed 100% of their MERob. Relative weight loss was higher in the RAPID group (P< 0·001) compared with the SLOW group. No linear relationship was found as a doubling of the percentage of energy restriction was accompanied by a tripling of the percentage of weight loss. Relative weight gain afterwards in the end-phase period was higher in the RAPID group (P< 0·001) compared with the SLOW and CONTROL groups. During the weight-loss period, TAG and NEFA concentrations were highest in the RAPID group, as were α-tocopherol and ferric-reducing ability of plasma concentrations. After 8 weeks of weight loss, the concentrations of advanced oxidation protein products were higher in the RAPID group compared with the SLOW and CONTROL groups (P< 0·001). In conclusion, the level of energy restriction influences the extent of changes in oxidant/antioxidant balance. Practically, more severe energy restriction regimens may be associated with a greater regain of weight after the restriction period.

Prepartal dietary energy alters transcriptional adaptations of the liver and subcutaneous adipose tissue of dairy cows during the transition period

Overfeeding during the dry period may predispose cows to increased insulin resistance (IR) with enhanced postpartum lipolysis. We studied gene expression in the liver and subcutaneous adipose tissue (SAT) of 16 Finnish Ayrshire dairy cows fed either a controlled energy diet [Con, 99 MJ/day metabolizable energy (ME)] during the last 6 wk of the dry period or high-energy diet (High, 141 MJ/day ME) for the first 3 wk and then gradually decreasing energy allowance during 3 wk to 99 MJ/day ME before the expected parturition. Tissue biopsies were collected at -10, 1, and 9 days, and blood samples at -10, 1, and 7 days relative to parturition. Overfed cows had greater dry matter, crude protein, and ME intakes and ME balance before parturition. Daily milk yield, live weight, and body condition score were not different between treatments. The High cows tended to have greater plasma insulin and lower glucagon/insulin ratio compared with Con cows. No differences in circulating glucose, glucagon, nonesterified fatty acids and β-hydroxybutyrate concentrations, and hepatic triglyceride contents were observed between treatments. Overfeeding compared with Con resulted in lower CPT1A and PCK1 and a tendency for lower G6PC and PC expression in the liver. The High group tended to have lower RETN expression in SAT than Con. No other effects of overfeeding on the expression of genes related to IR in SAT were observed. In conclusion, overfeeding energy prepartum may have compromised hepatic gluconeogenic capacity and slightly affected IR in SAT based on gene expression.