Abstract:
Preruminant male crossbred lambs, aged 1-2 days at the start of the experiment, were bottle-fed on milk replacers containing casein as the sole source of protein for an experimental period of 15-21 days. Choline-deficient diets were used in experiment 1 to determine the effect on the performance of the lambs of thc dictary protein concentration (10, 15 and 25% protein energy), and in experiment 2 of different sources of fat (butter oil, maize oil or lard), unsupplemented, or with supplements of choline chloride or L-cystine. Supplements of choline chloride decreased liver fat content and decreased urinary creatine excretion, irrespective of dietary protein concentration or source of dietary fat. Ira general, urinary ammonia excretion increased as the sulfur amino acid content of the diets increased, but there were interactions with the source of fat, so that although sulfur intake remained constant ammonia excretion was higher with diets containing lard than with those containing maize oil or butter oil. The effect of the supplements of 1,-cystine on liver fat content and urinary creatine excretion was not significantly different from that of the unsupplemented choline-deficient diets. In experiments 3 and 4 a choline-deficient diet with 25% protein energy and butter oil as the source of fat was supplemented with graded amounts of choline chloride. Energy intake was ad libitum, or restricted to 80% of ad libitum. When the lambs were fed ad libitum there was a significant decrease in liver fat content even with the smallest supplement of choline chloride (c. 9 mg MJ-1 gross energy), but no significant effect when energy intake was restricted. Since liveweight gains and nitrogen balances were unaffected by the presence or absence of the choline supplements it was concluded that in milk replacers containing 25% protein energy from casein, with butter oil as the source of fat, supplementation with choline chloride to provide 9 mg MJ-1 gross energy (233 mg kg-1 dry matter) would be sufficient to prevent the increased deposition of fat in the liver during the 6rst three weeks of life.