Veterinary Science - Theses
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ItemRelationships between diet, obesity and insulin dysregulation in horses and ponies( 2016)Laminitis is a debilitating condition of equids that affects a significant proportion of domesticated horses and ponies (Equus caballus) worldwide. Prevention is the key to managing laminitis, as there are currently no effective treatments and crippling lameness can often necessitate the euthanasia of affected animals. The clinical clustering of obesity and insulin dysregulation as risk factors for laminitis has been referred to as equine metabolic syndrome. The studies reported in this thesis sought to further examine the relationships between diet, obesity and insulin dysregulation in horses and ponies. Differences in the innate glucose and insulin dynamics of different equine breeds were established by investigating the insulin responses of animals to oral and intravenous glucose challenges. Ponies and Andalusian horses were relatively insulin resistant and hyperinsulinaemic compared with Standardbred horses; a finding that occurred without the potentially confounding effects of obesity or modifying dietary factors. Studies of diet-induced weight gain were then undertaken, in which a high dietary glycaemic load was found to influence the development of insulin dysregulation more than the induction of obesity per se. Relatively low plasma levels of adiponectin were identified in animals with reduced insulin sensitivity, whilst evidence of significant systemic inflammation was not detected. Glucagon-like peptide-1 (GLP-1) levels were found to correlate with postprandial insulin responses in horses and ponies adapted to cereal-rich meals. These studies report for the first time the identification of innate differences in insulin metabolism between particular equine breeds. The induction of obesity was not associated with insulin dysregulation in horses and ponies fed a low glycaemic diet, suggesting that increased adiposity might be a consequence rather than a cause of insulin dysregulation in equids. Adiponectin may be a potentially useful biomarker for insulin dysregulation, although whether hypoadiponectinaemia is involved in the pathogenesis requires further investigation. Incretins such as GLP-1 could represent a potential therapeutic target for the control of equine hyperinsulinaemia. Understanding how genetic predispositions to insulin dysregulation can be aggravated by the environment is an essential first step in the development of countermeasures to reduce the incidence of laminitis in equine populations worldwide.