Insulin Resistance as a Result of Body Condition Categorized as Thin, Moderate, and Obese in Domesticated U.S. Donkeys (Equus asinus)

Abstract Donkeys are often kept, especially in industrialized countries, as companion animals. Donkeys have greater digestive efficiency and tend to expend less energy than horses or ponies, which contributes to obesity in nonworking donkeys. Obesity in all equine species increases risk of chronic health conditions such as laminitis and insulin resistance. Previous studies in horses and ponies have documented obesity's potential effects on glucose-insulin dynamics with lower insulin sensitivity and higher insulin responses to glucose. However, limited studies on obesity and its health impacts in donkeys exist, so these effects on glucose-insulin dynamics have not been fully studied. Twenty-four donkeys were selected according to initial body condition score (BCS) and divided into three categories with eight donkeys in each: thin, moderate, and obese. A frequently sampled glucose-insulin tolerance test was performed with subsequent MINMOD analysis to determine the effects of BCS on glucose-insulin dynamics. Basal insulin was highest in obese donkeys when compared with moderate and thin donkeys ( P  = .02 and P  = .01, respectively). There was an overall trend across groups for BCS to lower insulin sensitivity ( P  = .06). No other effect was found. Body condition score seems to affect donkeys in a similar manner to horses and ponies as higher BCS was associated with higher basal insulin and may lower insulin sensitivity. Higher basal insulin concentrations in obese donkeys could negatively influence health and contribute to serious, chronic conditions.