中文摘要：

本试验旨在探究不同蛋白质水平补饲料对3月龄早期断奶犊牦牛生产性能、血液指标和胃肠道发育的影响。选取3月龄（90±5）日龄]健康大通母犊牦牛48头,随机分为4组,每组4个重复,每个重复3头。对照组犊牛全放牧,试验组犊牛在放牧基础上分别补饲不同蛋白质水平（粗蛋白质水平分别17%、18%、19%）的3种等能量（增重净能5.6 MJ/kg）饲粮。预试期7 d,正试期60 d。结果表明：1）与对照组相比,补饲能够显著提高犊牦牛的平均日增重,17%、18%和19%补饲组分别提高了28.87%、47.47%和28.61%（P〈0.05）。2）与对照组相比,补饲显著提高了血清尿素氮浓度（P〈0.05）,17%、18%和19%补饲组分别增加了10.57%、16.64%、21.84%（P〈0.05）。3）与对照组组相比,补饲料粗蛋白质水平为18%时,显著提高了瘤胃和大肠的绝对重量和相对重量（P〈0.05）,显著提高了十二指肠、盲肠、结肠的绒毛高度以及十二指肠和盲肠的绒毛高度/隐窝深度（P〈0.05）。因此,补饲能够提高早期断奶母犊牦牛生产性能和促进胃肠道发育,早期断奶母犊牦牛的补饲料的适宜粗蛋白质水为18%。

英文摘要：

This study was conducted to evaluate the effects of supplementary diets containing different levels of protein on performance, blood indexes and gastrointestinal development of early-weaned yak calves. Forty-eight healthy female Datong weaned yak calves aged about 3 months [（90 ± 5） days of age] were selected and assigned randomly to four groups with four replicates in each group and 3 heads per replicate. Yaks in con-trol group were grazed only, and those in experimental groups were grazed and fed isoenergetic （ net energy for gain=5.6 MJ/kg） supplementary diets contained 17%, 18% and 19% crude protein （ CP） , respectively. The pre-experiment lasted for 7 days, and the experiment lasted for 60 days. The results showed as follows： con-trast with control group, 1） the average daily gain were significantly increased by supplementary, and that in 17%, 18% and 19% supplementary groups was increased by 28.87%, 47.47%, 28.61% （ P〈0.05） , respec-tively;2） the supplementary significantly increased the concentration of serum urea nitrogen, and that in 17%, 18% and 19% supplementary groups was increased 10.57%, 16.64% and 21.84% （P〈0.05）, respectively;3 ） the absolute weight and the relative weight of rumen and large intestine were significantly enhanced by sup-plementary diet containing 18% CP （P〈0.05）, and the villus height of duodenum, caecum and colon, and villus height/crypt depth of duodenum and caecum were significantly improved, too （ P〈0.05） . These results indicate that supplementary diet is contributed to improve the production performance and gastrointestinal devel-opment of early-weaned female yak calves, and the optimal CP level is 18%.