关键词: 犊牛, 蛋白质, 氨基酸, 代乳品, 消化率

Abstract: This study was designed to examine the effects of different dietary protein levels on growth performance, nutrients utilization, and amino acid (AA) digestibility of early-weaning dairy calves. Fifteen healthy new born calves were randomly allotted into three experimental groups and fed three kinds of milk replacers with different protein levels (18%, 22% and 26%) respectively, labeled as LP, MP and HP group. The results showed that the body weight (BW) gain of MP group was higher than that of other groups (P<0.05), the ADG of three groups were 598.10, 829.52 and 628.57 g/d, respectively. The apparent digestibility of DM, EE and Ash were no difference among three groups (P>0.05), however, the apparent digestibility of CP in MP group was higher (P<0.05). Intake N and Fecal N increased as dietary protein content increasing (P<0.05), however, Urine N was unaffected by dietary CP levels significantly (P>0.05). The retained Ca, P and expressed as a percentage of intake N in MP group were all higher than that in other groups (P<0.05). The average digestibility of the total AA were 82.73%, 83.41% and 79.45% in LP, MP and HP groups, respectively, and the digestibility of amino acids（except for Ala） were no effected by CP levels (P>0.05). It was concluded that milk replacer with 22% CP produced higher body weight gain and better utilization of nutrients in comparison with lower protein and higher protein contents milk replacer.

Key words: calves, protein, amino acid, milk replacer, digestibility