Protein utilisation during energy undernutrition in sheep sustained on intragastric infusion: effect of changing energy supply on protein utilisation

Abstract

Eight sheep nourished by intragastric infusion were used to study the effect of volatile fatty acid (VFA) supply on protein utilisation. They received daily abomasal infusion of 1000 mg casein-N kg −1 W 0.75 and ruminal infusion of 250 kJ VFA kg −1 W 0.75. In four sheep the latter was increased from 250 kJ VFA kg −1 W 0.75 (20 days) to 560 kJ VFA kg −1 W 0.75 (20 days); in the other four it was reduced from 560 to 250 kJ VFA kg −1 W 0.75. Energy and N balances were measured. In all animals, creatinine excretion was nonsignificantly higher when 560 kJ VFA kg −1 W 0.75 were infused. Efficiency of VFA energy utilisation was higher when VFA energy was reduced than when it was increased (0.75 vs. 0.61). Although the animals were in negative energy balance during infusion of 250 kJ VFA kg −1 W 0.75, they attained positive N balance. N retention was further improved by increasing VFA supply from 250 to 560 kJ kg −1 W 0.75 but the extent varied between animals. The effect of fluctuating energy supply on protein metabolism may depend on the availability of endogenous energy contained in fat. It implies that provided protein supply is adequate, an animal can gain lean tissue fuelled by fat but the extent may depend on the fatness of the animal.