|Budget Amount *help
¥2,100,000 (Direct Cost: ¥2,100,000)
Fiscal Year 1993: ¥1,000,000 (Direct Cost: ¥1,000,000)
Fiscal Year 1992: ¥1,100,000 (Direct Cost: ¥1,100,000)
Calves weaned at 6 weeks of age are suitable at least under 3 months of age to examine limiting amino acids because of a limited synthesis of microbial protein in the under-developed rumen. Thus, for the first time the first limiting amino acids was examined when the diet consisted of 75.6% corn and 12.6% soybean meal (SBM) was given to male Holstein calves at th1e stage from weaning to 3 months of age. Intra-abomasal administration of the mixture of Lys and Met through the esophageal groove improved the nitrogen (N) balance (Expt, 1 and 2). Although the administraion of single Lys did not improve N balance (Expt.3 and 4), that of single Met increased N retention (Expt.5), suggesting a possibility of Mt being the first limiting amino acid. In contrast, the first limiting amino acid was Lys when the diet consisted of corn and corn gluten meal (CGM) and containing the similar level of crude protein (CP) was given to calves under 3months of age in our previous study. The present results i
dicated that diets would be a key factor which determines limiting amino acids also in cattle.
Above 3 months of age, larger amounts of microbial protein are synthesized in more developed rumen than under 3 months of age, resulting in a general difficulty to detect limiting amino acids, although the first limiting amino acid was Lys when the (corn +CGM) diet was given to calves above 3 months of age under the condition that the daily CP intake was 2.8 g per kg body weight in the previous study. Then, conditions of limiting amino acids being able to detect in calves given the (corn + SBM) diet to calves above 3 months of age (Expt.6,7 and 8). As a result, the synthesis of microbial protein in the rumen remarkably decreased when the daily CP intake from the (corn + SBM) diet was less than 2.8g/kg in 130-175 kg calves, although the production hardly declined within the range from 3.7 to 2.8 g/kg on account of an increase in recycled N.However, intra-abomasal administration of Met plus Lys (Expt.9) or Lys alone (Expt.10) via the esophageal groove did not increase N retention when calves above 3 months of age received the diet consisted of 82.8 % corn and 5.4% SBM under a condition that the daily CP intake was 2.7 g/kg, in contrast to the previous study. The discrepancy between the present and the previous studies might be due to the following factors : (1) the amino acid composition is rather compensatory between corn and SBM in contrast to the relation between cond and CGM, and (2) susceptibility of protein to degaradation in the rumen does not vary for CGM, which originally contains proteins hardly degraded in the rumen, independent of the development of the organ, but varies with the development for SBM which originally contains proteins easily degraded. Less