Influence of nutritional status on metabolic responses to exercise in donkeys

Abstract

SummaryThe metabolic consequences of submaximal exercise following long term nutritional deprivation were investigated in 6 donkeys. Animals were fed all roughage diets, either adequate (Timothy hay: H) or deficient in energy and protein (wheat straw: S) in a crossover design. After 8–10 weeks of dietary adaptation, responses to 60 min of moderate intensity draft loading exercise were compared. Jugular blood was sampled at rest and during exercise for glucose, lactate and free fatty acids (FFA) concentrations, haematocrit, Cortisol and insulin levels. Heart rate (HR) was monitored electronically. Resting lactate concentration was higher in animals fed hay (H) than in animals fed straw (S); only in S animals, however, did post exercise lactate concentration (1.55 ± 0.9 mmol/l) exceed pre‐exercise lactate concentration (0.6 ± 0.1 mmol/l). Hypoglycemia occurred in all animals in early exercise but was more pronounced in S animals. Straw‐fed animals had higher FFA concentrations at rest than H animals (mean ± s.e. 433 ± 71 vs. 102 ± 9 μmol/l). Plasma FFA concentrations declined precipitously in S animals at the onset of exercise, thereafter FFA increased over resting concentrations in both diets. Cortisol concentrations were higher at all times in H animals and increased during exercise regardless of diet. Insulin was lower in S animals and decreased during exercise in both diet groups. Resting HR was lower in S than in H animals (mean ± s.e. 34 ± 2 vs. 45 ± 2 beats/min). Exercising HR was greater in S animals. These data suggest that long term undernutrition in donkeys leads to decreased carbohydrate reserves, diminished maximal aerobic capacity and endocrine alterations. Work difficulty and stress level may increase, with possible negative implications for animal health and endurance.