Department of Animal Science, Universidade Federal de Viçosa, Peter Henry Rolfs Avenue, Viçosa, Minas Gerais36570-900, Brazil.
Department of animal Science, Institute of Studies of Humid Tropics, Universidade Federal do Sul e Sudeste do Pará, 31st Street, Block 07, Xinguara, Pará68557-335, Brazil.
Animal. 2020 Sep;14(9):1857-1866. doi: 10.1017/S1751731120000622. Epub 2020 Apr 6.
Nutrient requirements in cattle are dependent on physiological stage, breed and environmental conditions. In Holstein × Gyr crossbred dairy heifers, the lack of data remains a limiting factor for estimating energy and protein requirements. Thus, we aimed to estimate the energy and protein requirements of Holstein × Gyr crossbred heifers raised under tropical conditions. Twenty-two crossbred (½ Holstein × ½ Gyr) heifers with an average initial BW of 102.2 ± 3.4 kg and 3 to 4 months of age were used. To estimate requirements, the comparative slaughter technique was used: four animals were assigned to the reference group, slaughtered at the beginning of the experiment to estimate the initial empty BW (EBW) and composition of the animals that remained in the experiment. The remaining animals were randomized into three treatments based on targeted rates of BW gain: high (1.0 kg/day), low (0.5 kg/day) and close to maintenance (0.1 kg/day). At the end of the experiment, all animals were slaughtered to determine EBW, empty body gain (EBG) and body energy and protein contents. The linear regression parameters were estimated using PROC MIXED of SAS (version 9.4). Estimates of the parameters of non-linear regressions were adjusted through PROC NLIN of SAS using the Gauss-Newton method for parameter fit. The net requirements of energy for maintenance (NEm) and metabolizable energy for maintenance (MEm) were 0.303 and 0.469 MJ/EBW0.75 per day, respectively. The efficiency of use of MEm was 64.5%. The estimated equation to predict the net energy requirement for gain (NEg) was: NEg (MJ/day) = 0.299 × EBW0.75 × EBG0.601. The efficiency of use of ME for gain (kg) was 30.7%. The requirement of metabolizable protein for maintenance was 3.52 g/EBW0.75 per day. The equation to predict net protein requirement for gain (NPg) was: NPg (g/day) = 243.65 × EBW-0.091 × EBG. The efficiency of use of metabolizable protein for gain (k) was 50.8%. We observed noteworthy differences when comparing to ME and protein requirements of Holstein × Gyr crossbred heifers with other systems. In addition, we also observed differences in estimates for NEm, NEg, NPg, kg and k. Therefore, we propose that the equations generated in the present study should be used to estimate energy and protein requirements for Holstein × Gyr crossbred dairy heifers raised in tropical conditions in the post-weaning phase up to 185 kg of BW.
牛的营养需求取决于生理阶段、品种和环境条件。在荷斯坦×吉尔杂交奶牛后备牛中，缺乏数据仍然是估计能量和蛋白质需求的一个限制因素。因此，我们旨在估计在热带条件下饲养的荷斯坦×吉尔杂交后备牛的能量和蛋白质需求。使用了 22 头杂交（1/2 荷斯坦×1/2 吉尔）后备牛，平均初始 BW 为 102.2±3.4kg，年龄为 3 至 4 个月。为了估计需求，采用了比较屠宰技术：将 4 头动物分配到参考组，在实验开始时屠宰，以估计动物的初始空 BW（EBW）和组成，其余动物则根据目标 BW 增重率随机分为三组：高（1.0kg/天）、低（0.5kg/天）和接近维持（0.1kg/天）。在实验结束时，所有动物均被屠宰，以确定 EBW、空体增重（EBG）和体能量和蛋白质含量。使用 SAS（版本 9.4）的 PROC MIXED 程序估计线性回归参数。使用 SAS 的 PROC NLIN 通过高斯-牛顿法对非线性回归的参数进行调整，以适应参数拟合。维持的净能量需求（NEm）和可代谢能量用于维持（MEm）分别为 0.303 和 0.469MJ/EBW0.75/天。MEm 的利用效率为 64.5%。预测净能量用于增重（NEg）的估计方程为：NEg（MJ/天）=0.299×EBW0.75×EBG0.601。ME 用于增重（kg）的利用效率为 30.7%。维持的可代谢蛋白质需求为 3.52g/EBW0.75/天。预测净蛋白质用于增重（NPg）的方程为：NPg（g/天）=243.65×EBW-0.091×EBG。用于增重的可代谢蛋白质的利用效率（k）为 50.8%。与其他系统的荷斯坦×吉尔杂交后备牛的 ME 和蛋白质需求相比，我们观察到了显著的差异。此外，我们还观察到了 NEm、NEg、NPg、kg 和 k 的估计值差异。因此，我们建议在断奶后阶段至 185kg BW 期间，在热带条件下饲养荷斯坦×吉尔杂交奶牛后备牛时，应使用本研究中生成的方程来估计能量和蛋白质需求。
