Table_1_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头处于青春期前的三种品种组成（品种组成；荷斯坦、泽西和荷斯坦×泽西）的乳牛的维持和增重能量需求。针对0、400和800克/天的增重，设计了相应的日增重饲料配方，分别对应1.0倍、1.5倍和2.0倍的维持需求。每个品种的乳牛均包含六个初始体重（iBW）分别为219.8 ± 32公斤、215.8 ± 33公斤和228.3 ± 33公斤的动物，具体为荷斯坦、泽西和荷斯坦×泽西。实验采用3×3完全随机设计（三种品种组成和三种饲养水平），旨在通过粪便和尿液的消化代谢实验来确定能量损失。通过持续测量呼吸室内氧气消耗、二氧化碳排放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估算，其中RE为保留能量（Mcals/天），EBW为空体体重（kg0.75），EBG为空体增重（kg/天）。可消化能量用于增重的利用效率估计为RE与增重MEI回归线的斜率。泽西牛的NEm比荷斯坦×泽西杂交牛低15%（98 kcal/kg的BW0.75）。荷斯坦和杂交牛的NEm分别为102和112 kcal/kg的BW0.75。HG、荷斯坦和泽西的km分别为0.71、0.74和0.75。各品种组成间的净增重能量需求（NEg）无显著差异，对所有品种组成拟合了单一方程：RE = 0.069 × BW0.75 × BGW0.852。所有三种品种组成均观察到0.65的增重系数。品种组成影响了维持和能量分配的能量需求，这些差异在估算泽西、荷斯坦×泽西杂交牛和荷斯坦牛的能量需求时应当予以考虑。