Table_2_Energy requirements of Holstein, Gyr, and Holstein × Gyr crossbred heifers using the respirometry technique.docx

We aimed to determine the energy requirements for maintenance and gain of 18 prepubertal dairy heifers of three breed compositions (BC; Holstein, Gyr, and Holstein × Gyr). Diets were formulated for gains of 0, 400, and 800 g/day, corresponding to 1.0×, 1.5×, and 2.0× maintenance, respectively. Each dairy BC had six animals with an initial body weight (iBW) of 219.8 ± 32 kg, 215.8 ± 33 kg, and 228.3 ± 33 kg for Holstein, Gyr, and Holstein × Gyr, respectively. The experiment was designed as a completely randomized design in a factorial scheme 3 × 3 [three BC and three feeding levels (FL)]. Digestibility and metabolism assays were performed to determine energy losses through feces and urine. Heat production was determined using the continuous measurement of oxygen consumption, carbon dioxide production, and methane emissions in respiration chambers. Energy requirements for maintenance (NEm) were calculated based on the relationship between heat production (HP) and metabolizable energy intake (MEI). The efficiency of use of metabolizable energy for maintenance (km) was obtained from the ratio between NEm and metabolizable energy requirements for maintenance. The net energy requirements for growth (NEg) were estimated from the model RE = β0 × EBW0.75 × EBGβ1, where RE is the retained energy (Mcal/day), EBW is empty body weight (kg0.75), and EBG is the empty body gain (kg/day). The efficiency of use of metabolizable energy for gain (kg) was estimated as the slope of the regression between RE and MEI for gain. Gyr heifers presented NEm 15% lower (98 kcal/kg of BW0.75) than HG crossbred animals. Holstein and crossbred heifers had similar NEm, 102 and 112 kcal/kg of BW0.75, respectively. The km was 0.71, 0.74, and 0.75 for HG, Holstein, and Gyr, respectively. Net energy requirement for gain (NEg) did not differ across BC, and a single equation was fit for all BC: RE = 0.069 × BW0.75 × BGW0.852. A single kg of 0.65 was observed for all three BC. Breed composition affected the energy requirements for maintenance and the energy partition, and those differences should be considered when estimating requirements for Gyr, Holstein × Gyr crossbred, and Holstein heifers.

本研究旨在确定18头处于青春期前、由三种品种组成（品种组成；荷斯坦、盖尔、荷斯坦×盖尔）的乳牛的维持与增重能量需求。针对增重0、400和800克/天的需求，分别对应维持能量的1.0倍、1.5倍和2.0倍，设计了相应的饲料配方。每个品种的乳牛均包含6头初始体重（iBW）分别为219.8 ± 32公斤、215.8 ± 33公斤和228.3 ± 33公斤的个体，具体为荷斯坦、盖尔和荷斯坦×盖尔。实验以完全随机设计在3×3析因方案（三种品种组成和三种饲养水平）中进行。通过消化率和代谢实验，测定了通过粪便和尿液的能量损失。利用呼吸室内持续测量的氧气消耗、二氧化碳产生和甲烷排放来确定产热。维持能量需求（NEm）基于产热（HP）与可消化能量摄入（MEI）之间的关系进行计算。维持能量利用效率（km）通过NEm与维持能量需求的比值获得。净增重能量需求（NEg）通过模型RE = β0 × EBW0.75 × EBGβ1进行估算，其中RE为保留能量（Mcal/天），EBW为空体体重（kg0.75），EBG为空体重增重（kg/天）。可消化能量用于增重的利用效率估计为RE与增重MEI回归斜率。盖尔品种的乳牛的NEm比荷斯坦×盖尔杂交动物低15%（98 kcal/kg of BW0.75）。荷斯坦和杂交乳牛的NEm分别为102和112 kcal/kg of BW0.75。kg的km分别为0.71、0.74和0.75，分别对应HG、荷斯坦和盖尔品种。净增重能量需求（NEg）在不同品种组成间无差异，并为所有品种组成拟合了单一方程：RE = 0.069 × BW0.75 × BGW0.852。所有三个品种组成观察到单一kg的0.65。品种组成影响了维持能量需求和能量分配，这些差异在估算盖尔、荷斯坦×盖尔杂交和荷斯坦乳牛的需求时应当予以考虑。