Department of Dairy Science, Virginia Polytechnic Institute and State University, Blacksburg 24061, USA.
J Dairy Sci. 2010 Sep;93(9):4374-85. doi: 10.3168/jds.2010-3195.
The Virginia Tech crossbreeding project began in the fall of 2002 by mating Holstein (H) and Jersey (J) foundation females to Holstein and Jersey bulls to create HH, HJ, JH, and JJ genetic groups, where the sire breed is listed first followed by dam breed. Collection of individual daily feed intakes began in September 2005 and continued through November 2008, resulting in observations on 43, 34, 41, and 22 HH, HJ, JH, and JJ cows, respectively. Intakes were measured for 2 wk out of every 6-wk period for first-lactation cows less than 310 d in milk. The ration was analyzed for dry matter and nutrient content, which was used to calculate net energy of lactation (NEL, Mcal/kg). Body and milk weights were collected daily with milk components measured monthly. The NEL requirements for maintenance, growth (in the form of retained energy), pregnancy, and production were calculated using National Research Council (2001) equations. Random regression models were used to predict consumed NEL and NEL required for production, maintenance, and body weight at every week in lactation. Energy required for growth was calculated for each cow at each stage of lactation using five 2-mo stages. Energy balance was estimated by subtracting the predicted energy required for production, maintenance, growth, and pregnancy from the predicted NEL consumed. A linear model with fixed effects of genetic group, year-season of calving group, and a linear and quadratic effect of age at calving was used to analyze the energy terms. The HJ and JH groups were not different in any of the analyses for energy terms. The HH cows consumed more energy than did HJ and JJ cows. There were no genetic group differences for total energy for pregnancy. The HH, HJ, and JH groups were not different from each other for energy required for production but required more energy for production than the JJ. The JH allocated a lower percentage of their energy intake to maintenance than the HH (25.7 to 27.4%) and the JJ allocated less energy to growth than the HH and HJ. Genetic group explained significant variation for percentage of energy partitioned to production with the JJ allocating more energy to production than the HH (66.3 vs. 60.9%). Genetic group differences in characterization of energy balance warrant further study.
弗吉尼亚理工大学的杂交项目始于 2002 年秋季，当时将荷斯坦（H）和泽西（J）基础母牛与荷斯坦和泽西公牛交配，创建 HH、HJ、JH 和 JJ 遗传群体，其中列出了父本品种，然后是母本品种。2005 年 9 月开始收集个体每日采食量，并持续到 2008 年 11 月，分别对 43、34、41 和 22 头 HH、HJ、JH 和 JJ 奶牛进行了观察。对于头胎奶牛，在少于 310 天泌乳期的每 6 周周期中，每两周测量一次采食量。用干物质和营养成分分析日粮，用于计算泌乳净能（NEL，兆卡/千克）。每天收集体况和产奶量，每月测量乳成分。使用国家研究委员会（2001 年）方程计算维持、生长（以保留能量的形式）、妊娠和生产的净能需求。使用随机回归模型预测每头奶牛在泌乳期的每一周的消耗 NEL 和生产、维持和体重所需的 NEL。使用五个 2 个月阶段，为每个奶牛在泌乳的每个阶段计算生长所需的能量。通过从预测的消耗 NEL 中减去预测的生产、维持、生长和妊娠所需的能量来估计能量平衡。使用固定遗传群体、产犊季节组的年季节和产犊年龄的线性和二次效应的线性模型来分析能量项。在能量项的任何分析中，HJ 和 JH 群体都没有差异。HH 奶牛消耗的能量多于 HJ 和 JJ 奶牛。对于妊娠总能量，没有遗传群体差异。HH、HJ 和 JH 群体之间的生产所需能量没有差异，但比 JJ 群体需要更多的生产能量。JH 群体将其能量摄入量的较低百分比分配给维持（25.7%至 27.4%），而 JJ 群体将较少的能量分配给生长，比 HH 和 HJ 群体。遗传群体对生产中能量分配比例的解释具有显著差异，JJ 群体比 HH 群体（66.3%对 60.9%）分配更多的能量用于生产。能量平衡的遗传群体差异值得进一步研究。
