Comparison of Feed Digestibility between Ponies, Standardbreds and Andalusian Horses Fed Three Different Diets.

Ponies and some horse breeds such as Andalusians exhibit an 'easy keeper' phenotype and tend to become obese more readily than other breeds such as Standardbreds. Various hypotheses have been proposed, including differences in appetite or metabolic efficiency. This study aimed to investigate the effect of breed on nutrient digestibility. Ponies, Standardbreds and Andalusian horses were adapted to consuming either a control fibre-based diet (n = 9), a hypercaloric cereal-rich diet (n = 12) or a hypercaloric fat-rich diet (n = 12) over 20 weeks. Total faecal collection was performed over 24 h to determine apparent total tract digestibility of gross energy, dry matter (DM), neutral detergent fibre (NDF), starch, crude protein and crude fat. There was no effect of breed on apparent digestibility for any of the nutrients studied (all p > 0.05). However, there was a significant effect of diet, with animals consuming the cereal-rich or fat-rich diets demonstrating higher digestibility of gross energy, DM, NDF and crude protein compared with those consuming the control diet (all p < 0.05). Animals adapted to the cereal-rich diet demonstrated higher digestibility of starch (p < 0.001) and animals adapted to the fat-rich diet demonstrated higher digestibility of fat (p < 0.001). This study found that horses and ponies had similar nutrient digestibility when adapted to the same diets and management conditions. Limitations included the relatively small number of animals from each breed per diet group and the short period of total faecal collection. The tendency towards increased adiposity in ponies and Andalusian-type horse breeds is more likely to reflect differences in metabolism, rather than differences in feed digestibility.

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.

The effect of insulin on equine lamellar basal epithelial cells mediated by the insulin-like growth factor-1 receptor.

BACKGROUND: In horses and ponies, insulin dysregulation leading to hyperinsulinemia may be associated with increased risk of laminitis, and prolonged infusion of insulin can induce the condition. It is unclear whether insulin may have a direct or indirect effect on the lamellar tissues. Insulin is structurally related to insulin-like growth factor (IGF-1), and can bind the IGF-1 receptor, albeit at a lower affinity than IGF-1. METHODS: Immunohistochemistry was performed on formalin-fixed lamellar tissue sections from six normal horses, euthanised for non-research purposes, using an anti-IGF-1 receptor antibody. In further studies, lamellar epithelial cells were obtained by collagenase digestion from the hooves of 18 normal horses, also euthanised for non-research purposes, and incubated for 48 h in the presence of insulin (0-2,000 m IU/ml). The increase in cell numbers was determined using a cell proliferation assay, and compared to the effect of zero insulin using one-way ANOVA. RESULTS: Immunohistochemistry demonstrated IGF-1 receptors on lamellar epidermal epithelial cells. With cultured cells, insulin caused a concentration-dependent increase in cell proliferation compared to untreated cells (maximal effect 63.3 ± 12.8% more cells after 48 h with 1,000 m IU/ml insulin; P < 0.01). Co-incubation with a blocking antibody against the IGF-1 receptor significantly inhibited the proliferative effect of insulin (P < 0.01). DISCUSSION: These results demonstrate that IGF-1 receptors are present on lamellar epithelial cells. At high physiological concentrations, insulin may activate these cells, by a mechanism involving IGF-1 receptors, resulting in a proliferative effect. This mechanism could help to explain the link between hyperinsulinemia and laminitis.

Comparison and validation of ELISA assays for plasma insulin-like growth factor-1 in the horse.

Insulin-like growth factor-1 (IGF-1) plays several important physiological roles, and IGF-related pathways have been implicated in developmental osteochondral disease and endocrinopathic laminitis. This factor is also a downstream marker of growth hormone activity and its peptide mimetics. Unfortunately, previously used assays for measuring equine IGF-1 (radioimmunoassays and ELISAs) are no longer commercially available, and many of the kits on the market give poor results when used on horse samples. The aim of the present study was to compare three different ELISA assays (two human and one horse-specific). Plasma samples from six Standardbreds, six ponies and six Andalusians were used. The human IGF-1 ELISA kit from Immunodiagnostic Systems (IDS) proved to be the most accurate and precise of the three kits; the other two assays gave apparently much lower concentrations, with poor recovery of spiked recombinant human IGF-1 and unacceptably poor intra-assay coefficients of variation (CV). The IDS assay gave an intra-assay CV of 3.59 % and inter-assay CV of 7.31%. Mean percentage recovery of spiked IGF-1 was 88.82%, and linearity and dilutional parallelism were satisfied. The IGF-1 plasma concentrations were 123.21 ±8.24 ng/mL for Standardbreds, 124.95 ±3.69 ng/mL for Andalusians and 174.26 ±1.94 ng/mL for ponies. Therefore of the three assays assessed, the IGF-1 ELISA manufactured by IDS was the most suitable for use with equine plasma samples and may have many useful applications in several different research areas. However, caution should be used when comparing equine studies where different analytical techniques and assays may have been used to measure this growth factor.