Factors affecting clinical assessment of insulin sensitivity in horses

Insulin resistance is thought to be involved in the pathogenesis of many equine conditions such as pars intermedia dysfunction, equine metabolic syndrome, diabetes mellitus, hyperlipaemia, laminitis, endotoxaemia and osteochondrosis dissecans (OCD); whereas polysaccharide storage myopathy in Quarter Horses and equine motor neuron disease (EMD) have been associated with increased insulin sensitivity. However, it is clear that there is not one ideal test, in terms of both practicality and accuracy, for evaluating insulin sensitivity in horses and improved diagnostic techniques are required. This review sets out the background to the subject and identifies current knowledge regarding the measurement of insulin sensitivity by tolerance testing and clamping techniques. Factors affecting insulin sensitivity, such as breed, pregnancy, lactation, obesity and nutritional factors are discussed. In addition, the relationship with training, nutritional supplementation and drug administration are considered.