Silva F A S, Valadares Filho S C, Rennó L N, Zanetti D, Costa E Silva L F, Godoi L A, Vieira J M P, Menezes A C B, Pucetti P, Rotta P P
Animal Science Department, Universidade Federal de Viçosa, Viçosa, Minas Gerais, Brazil.
J Anim Physiol Anim Nutr (Berl). 2018 Feb;102(1):82-93. doi: 10.1111/jpn.12661. Epub 2017 Mar 16.
There is little information regarding the nutritional requirements for dairy heifers, leading the majority of nutrient requirement systems to consider dairy heifers to be similar to beef heifers. Therefore, we evaluated the muscle protein metabolism and physical and chemical body composition of growing Holstein × Gyr heifers and estimated the energy and protein requirements. We performed a comparative slaughter experiment with 20 Holstein × Gyr heifers at an initial body weight of 218 ± 36.5 kg and an average age of 12 ± 1.0 months. Four heifers were designated as the reference group, and the 16 remaining heifers were fed ad libitum. The 16 heifers were distributed using a completely randomized design in a 2 × 2 factorial arrangement with two roughages (corn silage or sugarcane) and two concentrate levels (30 or 50%) for 112 days. Greater (p < 0.05) values for fractional rates of muscle protein synthesis, degradation and accretion were observed for heifers that were fed 50% concentrate. The following equations were obtained to estimate the net energy for gain (NE ) and net protein for gain (NP ): NE (Mcal/day) = 0.0685 × EBW × EBWG and NP (g/day) = 203.8 × EBWG - 14.80 × RE, respectively, in which EBW is the empty body weight, EBWG is the empty body weight gain and RE is the retained energy. We concluded that increased rates of protein turnover are achieved when a greater quality diet is provided. In the future, these results can be used to calculate the nutritional requirements for growth of Holstein × Gyr heifers after equation validation rather than using the recommendations provided by other systems, which use values developed from beef heifers, to determine the nutritional requirements of dairy cattle.
关于奶牛小母牛的营养需求，目前几乎没有相关信息，这使得大多数营养需求系统认为奶牛小母牛与肉牛小母牛相似。因此，我们评估了生长中的荷斯坦×吉尔小母牛的肌肉蛋白质代谢以及身体的物理和化学成分，并估算了能量和蛋白质需求。我们对20头初始体重为218±36.5千克、平均年龄为12±1.0个月的荷斯坦×吉尔小母牛进行了比较屠宰实验。四头小母牛被指定为参考组，其余16头小母牛自由采食。这16头小母牛采用完全随机设计，按照2×2析因安排，分为两种粗饲料（玉米青贮或甘蔗）和两种精料水平（30%或50%），饲养112天。采食50%精料的小母牛的肌肉蛋白质合成、降解和沉积的分数率更高（p<0.05）。由此得出了估算增重净能量（NE）和增重净蛋白质（NP）的方程：NE（兆卡/天）=0.0685×空体重×空体重增重，NP（克/天）=203.8×空体重增重 - 14.80×留存能量，其中EBW为空体重，EBWG为空体重增重，RE为留存能量。我们得出结论，提供质量更高的日粮时，蛋白质周转率会提高。未来，在方程验证后，这些结果可用于计算荷斯坦×吉尔小母牛生长的营养需求，而不是使用其他系统提供的建议（这些建议使用从肉牛小母牛得出的值）来确定奶牛的营养需求。
