Abstract:
Preruminant male crossbred lambs, aged between 2 and 5 days at the start of the experiment, were given milk replacers in the following experiments. Experiment 1 : low (0.10 protein energy) or medium protein (0.25 protein energy) diets that contained whole egg as the sole source of protein, before or after autoclaving at 105�_ for 60 min. A medium protein diet that contained cows' milk protein was the control treatment. Experiment 2: low protein diets that contained either whole egg (before or after solvent extraction), solvent-extracted egg yolk, egg albumen or dried skim milk as the protein source, with butter oil or egg fat as the fat source. Experiment 3: low protein diets with solvent-extracted egg yolk as the protein source, butter oil as the fat source and supplemented with DL-methionine to raise the concentration of methionine + cystine to that of wholeegg or of egg albumen. Experiment 4: low protein diets containing either solvent-extracted egg yolk or cows' milk as protein source with butter oil as fat source, at a range of intakes of gross energy. All diets were supplemented with DL-methionine to raise the methionine + cystine concentration to that of whole egg. Nitrogen balances, liveweight gains and efficiencies of nitrogen utilization were determined with all diets for a 7-day collection period. All diets containing egg fat were poorly accepted and the digestibility of egg fat was low compared with butter oil. An experiment with weanling rats (experiment 5) showed that the reduction in fat digestibility could not be attributed to the phospholipid component of egg fat. The apparent digestibility of egg fat by rats was significantly less than that of coconut fat or groundnut oil in control diets. Low and medium protein diets containing autoclaved whole egg were more acceptable, and there was a significant increase in apparent nitrogen digestibility in the low protein diet compared with the diet containing unheated whole egg. Utilization of nitrogen in diets containing egg albumen was lower than in diets containing only the egg yolk fraction of whole egg. The addition of DL-methionine to solvent-extracted egg yolk to raise the methionine + cystine content to that of whole egg or egg albumen failed to increase nitrogen balances significantly. An attempt was made in experiment 4 to compare, by the slope-ratio method, the nutritive values of diets containing either egg yolk or cows' milk proteins, with DL-methionine added to raise the methionine + cystine content to that of whole egg. The diets that contained egg yolk were poorly accepted at the higher intake levels, whereas those containing cows' milk were readily accepted at all energy levels. The intercepts of the regression equations relating nitrogen balance to apparently digested nitrogen intake were significantly different. Thus the results did not meet the criteria proposed by Hegsted and Chang (1965) for a valid comparison by the slope-ratio method. A comparison of nitrogen balances, at the mean nitrogen intake of 596 mg nitrogen per day per kg0,73, showed significantly higher nitrogen balances for lambs given the milk protein diet than for those given the egg yolk diet (396 o. 324 mg nitrogen per day per kg0.73). There were no significant differences in liveweight gain. It was concluded that when the intake of apparently digested nitrogen was low (<477 mg nitrogen per day per kg0.73) the absorbed nitrogen from the egg yolk diet was more efficiently utilized than the apparently digested nitrogen from the milk diet, whilst above 477 mg nitrogen per day per kg0.73 the converse was true.