| Summary: | 1. Like other newly born ruminants, newly born lambs depend on their digestive enzyme system for the digestion and utilization of their diets, and ewe's or cow's milk appears to be the most suitable food for these animals. There is a great demand for developing substitutes to milk. The literature concerning the possibility of substituting the major constituents of milk and the problems associated with such a practice was reviewed. It was concluded that the lack of clotting of non-milk proteins, inadequate enzymes output, and possibly poor susceptibility of non-milk constituents to enzyme hydrolysis are some of the main factors limiting their use in milk substitutes. To eliminate the effects of these factors, partially or completely, an automated unit was developed so that non-milk constituents could be given in small meals frequently (8 times/day). They were also given in their raw form or in a partially hydrolysed form. 2. The effects of replacing milk constituents were studied in feeding trials which usually began at 7 days old, for 33 days, followed by balance trials for 7 days. A total of 128 lambs were used in these trials. Sixteen lambs, usually 8 males and 8 females, were used in each trial, which consisted of four groups each of four lambs. In some experiments the flow and apparent digestibilities in the terminal ileum were studied using four lambs about 3 weeks old, fitted with re-entrant cannulas in the small intestine. Thirty rats were used in a growth and N-retention trial to examine the effect of acid treatment and amino acid supplementation on the nutritive value of Toprina yeast. Four lambs were used in a growth trial to study the effect of high 2a intake cm growth and general health. Six lambs were used in digestibility trials to study the effect of drying on the nutritive value of FFH. Toprina yeast, its hydrolysates (partial hydrolysis using MCI or papain), or as broken cells (physical means), and undrled FPH were examined as substitutes for milk proteins. A mixture of lard and coconut fats of (90:10) was tested as a substitute for milk fat, in the presence of milk or non-railk proteins. Partially hydrolysed starch (protaayl 110) was examined as a substitute to glucose, lactose and proportions of milk fat. 3. Effect of replacing milk proteins: In Experiment 1, Toprina yeast was found to be an inferior protein source to skim milk. In Experiment 2 it was found that about 1/3 of casein could be replaced with Toprina yeast with little or no effect on lamb performance. Apparent digestibility of yeast nitrogen (80 to 84%) was lower than that of akira milk (93%) or casein (95%). In Experiment 3, partial hydrolysis of Toprina yeast with Hd improved its apparent digestibility in the small intestine from (60 to 67%) to (78%). The difference in N-digestibility between untreated yeast and milk was over 20 units in the small intestine, and this difference was greater than that recorded on intact animals (9 to 13 units) in Experiments 1 and 2.
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