Abstract
1) Experiments were carried out to investigate the effects of the substitution of commercial soybean flour of 50-55% crude protein for skim milk in the milk replacer of a practical formula on the digestibility and the growth of young calves. It was also examined to predict amino acid adequacy or availability of intact protein in milk replacer from the concentrations of plasma free amino acids. 2) Twenty-four Holstein male calves, averaging 45kg initially, were devided into three groups of eight calves each, and the groups were alloted to one of the three milk replacers containing (1) 57% skim milk and 15% whey powder, (2) 30% skim milk, 30% whey powder and 15% soybean flour, and (3) 40% whey powder and 35% soybean flour, respectively. Each milk replacer contained 10% fish soluble-adsorbed feed of 32% crude protein, as an additional protein source. During two weeks at the beginning of the growth trial of 13 weeks, calves were fed a definite amount of milk replacer from open pails, and in this period, the digestibility and the plasma amino acid concentrations were determined for three calves each in every group. After this period, calves were fed commercial calf starter and rice straw ad. lib. in addition to each milk replacer, and weaned after 35 days from the start of the experiment. 3) There were tendencies for depressed gains of body weight as well as the reduced growth of body length, withers height and chest girth of calves in the group rceeiving the milk replacer (3), though the differences among the groups were almost insignificant. 4) Apparent digestibilities of dry matter, crude protein and crude fiber of the milk replacer (3) were significantly lower than the corresponding values for the replcers (1) and (2), and no significant difference was detected between the latter two milk replacers. 5) On the 14th day, plasma concentrations of total free amino acids as well as valine, methionine, lysine, leucine, isoleucine, arginine and tyrosine were significantly higher for calves receiving the replacer (1), and no difference was observed between the group (2) and the group (3). 6) The glucose feeding resulted in the increase in blood glucose concentrations and the decrease in total plasma amino acid concentrations in all calves. The ratios of the plasma levels of individual essential amino acid 4 hours after the glucose feeding to the pre-feeding levels (PAAI) were lowest for lysine in the group (1) and isoleucine in the groups (2) and (3). 7) Additional three Holstein male calves, weighing about 45 kg initially, were fed only whole milk from nipple pails, and the concentrations of plasma free amino acids were determined on the 14th day. The ratio of each essential amino acid level in the plasma of calves fed each milk replacer to that of calves fed whole milk (PAARI) was lowest for methionine in the groups (1) and (2) and the both of methione and lysine in the group (3). 8) PAARI was considered to be superior to PAAI as a procedure for predicting the limiting amino acids of test protein, and cosequently, it was indicated that methionine was liable to be limiting even in the milk replacer containing 57% skim milk and 15% whey powder, and that lysine is also to be limiting amino acid as the increase of soybean flour substituted for skim milk in the milk replacer for young calves.
