Growth, Nutrient Utilization and Amino Acid Digestibility of Dairy Calves Fed Milk Replacers Containing Different Amounts of Protein in the Preruminant Period*

This study was designed to examine the effects of different dietary protein levels on growth performance, nutrient utilization, amino acid (AA) digestibility and serum biochemical parameters of preruminant dairy calves. Fifteen healthy new-born calves were randomly allotted to three experimental groups and fed with different milk replacer that contained 18% (LP), 22% (MP) or 26% (HP) of protein. The results showed that final BW, net gain and ADG were significantly higher in the MP group than in LP and HP groups (p<0.05). In addition, the apparent digestibility of CP in the MP group was significantly higher than in the other two groups (p<0.05). The values of N intake and fecal N excretion were significantly increased following the increase of dietary protein content (p<0.05). However, in all three groups of animals, dietary protein content had no significant effect on urinary N concentration (p>0.05). BUN concentration, on the other hand, decreased as calves grew but increased following the increase of dietary CP content. Furthermore, no significant differences in digestibility of amino acids were observed among these three groups of animals (p>0.05). We concluded that calves fed with milk replacer containing 22% of protein had better growth performance and nutrient utilization as compared to animals treated with milk replacer containing either 18% or 26% of protein. (