本研究旨在探讨12~13月龄湘中黑牛的粗蛋白质代谢规律与需要量。试验选择30头体况良好、体重 相近的12~13月龄湘中黑牛公牛,采用完全随机试验设计,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1.0 kg/d所需粗蛋白质的70%(Ⅰ组)、85%(Ⅱ组)、100%(Ⅲ组)、115%(Ⅳ组)、130%(Ⅴ组)配制的5种不同粗蛋白质水平的试验饲粮。采用饲养试验和消化代谢试验测定湘中黑牛生长性能及粗蛋白质代谢指标,并建立粗蛋白质需要量预测模型。预试期7 d,正试期50 d。结果表明:湘中黑牛的平均日增重与粗蛋白质采食量和可消化粗蛋白质采食量呈高度线性正相关(R²=0.926、R²=0.945);粗蛋白质消化率、粗蛋白质沉积率和粗蛋白质生物学效价平均值分别为(66.5±5.0)%、(36.6±8.7)%、(54.4±9.3)%,并且粗蛋白质消化率随粗蛋白质采食量的增加而显著增加(P<0.05),Ⅳ、Ⅴ组的粗蛋白质沉积率和粗蛋白质生物学效价显著高于Ⅰ、Ⅲ组(P<0.05);不同体重和日增重的湘中黑牛粗蛋白质和可消化粗蛋白质需要量方程分别为CP=5.29W^0.75+430.69×DG (R²=0.995,P<0.001,n=15);DCP=2.66W^0.75+377.95×DG (R²=0.994,P<0.001,n=15)。式中,CP为粗蛋白质需要量(g/d);DCP为可消化粗蛋白质需要量(g/d);W^0.75为单位代谢体重(kg);DG为日增重(kg/d)。湘中黑牛的维持粗蛋白质和可消化粗蛋白质需要量分别为5.29、2.66 g/(kg W^0.75·d),每千克增重的粗蛋白质和可消化粗蛋白质需要量分别为430.69、377.95 g。

This experiment was conducted to explore the crude protein metabolism and requirement of 12 to 13-month-old Xiangzhong black cattle. Thirty healthy Xiangzhong black cattle with a similar body weight of (273.77±15.97) kg, aged 12 to 13 months of age were selected and randomly divided into 5 groups with 6 replicates in each group. Beef cattle were fed 5 diets with different levels of crude protein which were formulated according to the expected weight gain 1.0 kg/d of crude protein required for 70% (group Ⅰ), 85% (group Ⅱ), 100% (group Ⅲ), 115% (group Ⅳ) and 130% (group Ⅴ), respectively. Feeding test and digestion and metabolism test were carried out to measure the growth performance and crude protein metabolism indexes of Xiangzhong black cattle, and to build the models for predicting the crude protein requirement. Pre-test period was 7 d and test period was 50 d. The results showed as follows: there was a high degree of positive linear correlation between average daily gain and crude protein intake or digestible crude protein intake (R²=0.926, R²=0.945); crude protein digestibility, crude protein deposition rate and crude protein biological value were (66.5±5.0)%, (36.6±8.7)% and (54.4±9.3)%, respectively; crude protein digestibility was gradually increased as the increase of crude protein intake (P<0.05), and crude protein deposition rate and crude protein biological value in groups Ⅳ and Ⅴ were significantly greater than those in groups Ⅰ and Ⅲ (P<0.05); crude protein and digestible crude protein requirements for Xiangzhong black cattle could be estimated by the equations:CP=5.29W^0.75+430.69×DG; DCP=2.66W^0.75+377.95×DG. CP represented crude protein requirement (g/d); DCP represented the requirement of digestible crude protein (g/d); W^0.75 represented the units of metabolic body weight (kg); DG represented daily gain (kg/d). The crude protein and digestible crude protein requirements for maintenance of Xiangzhong black cattle are 5.29 and 2.66 g/(kg W^0.75·d), respectively. Crude protein and digestible crude protein requirements for per kilogram gain are 430.69 and 377.95 g, respectively.