Effects of exercise and plane of nutrition on nutrient utilization by the hind limb of the sheep

Net uptake, by the hind limb, of oxygen and a number of energy substrates was measured in sheep fed semicontinuously at maintenance or 1.5 times maintenance, while standing at rest or walking on a moving-belt treadmill at 0.7 ms-1, on a 10 degrees slope for 60 min. Exercise caused a six- to sevenfold increase in hind-limb oxygen uptake, due mainly to increased blood flow, assisted by an increase in the oxygen-carrying capacity of arterial blood. Major changes in nutrient supply and utilization included hyperglycaemia, hyperlactacidaemia, free fatty acid (FFA) mobilization, and substantially increased uptakes of glucose and FFA by the hind limb. Acetate uptake was unchanged during exercise in maintenance-fed sheep, but was significantly increased in sheep fed at levels above maintenance. Plane of nutrition had little effect on hind-limb uptake of other nutrients in resting or exercising animals. Plasma FFA were clearly the most important respiratory fuels for exercising muscle, but a previous finding that acetate utilization was negligible during exercise was not confirmed. Possible reasons for this discrepancy between present and earlier results are discussed.