本试验旨在研究生长期秦川牛蛋白质沉积效率及小肠可消化粗蛋白质（IDCP）需要量（rIDCP）。试验选择30头体况良好、体重[（289.33±17.79）kg]相近的生长期秦川牛公牛，随机分为5组，每组6头牛，分别饲喂按我国《肉牛饲养标准》（NY/T 815—2004）提供的预期日增重0.9 kg/d所需IDCP的75.0%（Ⅰ组）、87.5%（Ⅱ组）、100.0%（Ⅲ组）、112.5%（Ⅳ组）、125.0%（Ⅴ组）配制的5种试验饲粮。采用饲养试验和消化代谢试验测定秦川牛生长性能及氮代谢指标，并建立粗蛋白质（CP）需要量（rCP）和rIDCP预测模型。预试期10 d，饲养试验42 d，消化代谢试验4 d。结果表明：1）秦川牛的平均日增重（ADG）与CP（R²=0.928，P<0.05）和IDCP采食量（R²=0.912，P<0.05）呈线性正相关；Ⅳ和Ⅴ组的料重比显著地低于其他各组（P<0.05）。2）随饲粮IDCP水平的提高，采食氮、沉积氮、粪氮、尿氮、氮的沉积率和氮的表观消化率均增加，其中采食氮、沉积氮组间均差异显著（P<0.05），Ⅳ组和Ⅴ组之间粪氮、尿氮、氮的沉积率和氮的表观消化率差异不显著（P<0.05）。综上所述，秦川牛的ADG与IDCP采食量呈线性正相关；饲粮IDCP水平的提高，有助于提高秦川牛的蛋白质沉积效率；生长期秦川牛rCP和rIDCP方程分别为：rCP（g/d）=5.94×W^0.75（kg）+470.84×ADG（kg/d）（R²=0.937，P<0.05）；rIDCP（g/d）=3.71×W^0.75（kg）+285.22×ADG（kg/d）（R²=0.942，P<0.05）（式中W^0.75为代谢体重）。生长期秦川牛的维持rCP和rIDCP分别为5.94和3.71 g/（kg W^0.75·d），每千克增重的rCP和rIDCP分别为470.84和285.22 g。

This experiment was conducted to investigate the protein deposition efficiency and intestinal digestible crude protein (IDCP) requirement (rIDCP) of growing Qinchuan cattle. Thirty healthy growing bulls of Qinchuan cattle with similar body weight were selected and randomly divided into 5 groups with 6 heads in each group. Cattle were fed 5 diets with different levels of IDCP which were formulated according to the rIDCP at an expected weight gain of 0.9 kg/d, and dietary IDCP levels were 75.0% (group Ⅰ), 87.5% (group Ⅱ), 100.0% (group Ⅲ), 112.5% (group Ⅳ) and 125.0% (group Ⅴ), respectively. Feeding test and digestion and metabolism test were carried out to measure the growth performance and protein deposition efficiency of growing Qinchuan cattle, and to build the models for predicting crude protein (CP) requirement (rCP) and rIDCP. Pre-test period was 10 days, feeding test period was 42 days, and digestion and metabolism test was 4 days. The results showed as follows: 1) there was positive linear correlation between average daily gain (ADG) and CP intake (R²=0.928, P<0.05), and between ADG and IDCP intake (R²=0.912, P<0.05); feed to gain ratio in groups Ⅳ andⅤ was significantly higher than that in the other groups (P<0.05). 2) With the increase of dietary IDCP level, nitrogen intake, nitrogen retention, fecal nitrogen, urinary nitrogen, nitrogen deposition rate and nitrogen apparent digestibility were increased, and there were significant differences in nitrogen intake and nitrogen retention among all groups (P<0.05), while there was no significant differences in fecal nitrogen, urinary nitrogen, nitrogen deposition rate and nitrogen apparent digestibility between groups Ⅳ and Ⅴ (P>0.05). In conclusion, there is a positive linear correlation between ADG and IDCP intake of Qinchuan cattle; the increase of dietary IDCP level is helped for improving protein deposition efficiency of Qinchuan cattle; the rCP and rIDCP for growing Qinchuan cattle can be estimated by the following equations: rCP (g/d) = 5.94×W^0.75 (kg) + 470.84×ADG (kg/d) (R²=0.937, P<0.05); rIDCP (g/d)=3.71×W^0.75 (kg)+285.22×ADG (kg/d) (R² = 0.942, P<0.05) (W^0.75 is metabolic weight). The rCP and rIDCP for maintenance of growing Qinchuan cattle are 5.94 and 3.71 g/(kgW^0.75·d), respectively. The rCP and rIDCP for per kilogram of weight gain of growing Qinchuan cattle are 470.84 and 285.22 g, respectively.