Nitrogen and purine metabolism at varying energy and protein supplies in sheep sustained on intragastric infusion.

Wether sheep were fitted with rumen fistulas and polyethylene tubes to the abomasum and were given all nutrients by intragastric infusion. In Expt 1 volatile fatty acids (VFA) were given at 340, 450 and 630 kJ gross energy (GE)/kg metabolic weight (W0-75) and protein at 0, 150, 300, 600, 900 and 1500 mg nitrogen/kg W0-75. In Expt 2 VFA were infused at 450 kJ GE/kg W0-75 and protein at 0 and 300 mg N/kg W0-75. At all levels of energy intake in Expt 1 the N retention was significantly (P less than 0.01) related to N intake. The basal N requirement was estimated to be 281 mg (SE 21.8) N/kg W0-75 at 340 kJ VFA/kg W0-75, 226 (SE 21.8) mg N/kg W0-75 at 450 kJ VFA/kg W0-75 and 207 (SE 19.4) mg N/kg W0-75 at 630 kJ VFA/kg W0-75. Plasma urea concentrations varied markedly in relation to protein intake and to energy supply. On the other hand plasma ammonia, glucose, insulin and creatinine concentrations, and also urinary excretion of purine derivatives and creatinine were not significantly affected by the treatments imposed. It was concluded that the urinary excretion of purine derivatives in ruminants was largely unaffected by moderate changes in energy intake and by large changes in protein intake.