PROTEIN-UTILIZATION DURING ENERGY UNDERNUTRITION IN SHEEP SUSTAINED ON INTRAGASTRIC INFUSION - EFFECT OF CHANGING ENERGY SUPPLY ON PROTEIN-UTILIZATION

Eight sheep nourished by intragastric infusion were used to study the effect of volatile fatty acid (VFA) supply on protein utilisation. The y received daily abomasal infusion of 1000 mg casein-N kg(-1) W-0.75 a nd ruminal infusion of 250 kJ VFA kg(-1) W-0.75. In four sheep the lat ter was increased from 250 kJ VFA kg(-1) W-0.75 (20 days) to 560 kJ VF A kg(-1) W-0.75 (20 days); in the other four it was reduced from 560 t o 250 kJ VFA kg(-1) W-0.75. Energy and N balances were measured, In al l animals, creatinine excretion was nonsignificantly higher when 560 k J 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 dur ing infusion of 250 kJ VFA kg(-1) W-0.75, they attained positive N bal ance. N retention was further improved by increasing VFA supply from 2 50 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 o n the availability of endogenous energy contained in fat. It implies t hat provided protein supply is adequate, an animal can gain lean tissu e fuelled by fat but the extent may depend on the fatness of the anima l.