Department of Primary Industries, Tatura Centre, Tatura, Victoria, Australia.
J Dairy Sci. 2011 Sep;94(9):4715-25. doi: 10.3168/jds.2010-4015.
Feed conversion efficiency of dairy cattle is an important component of the profitability of dairying, given that the cost of feed accounts for much of total farm expenses. Residual feed intake (RFI) is a useful measure of feed conversion efficiency, as it can be used to compare individuals with the same or differing levels of production during the period of measurement. If genetic variation exists in RFI among dairy cattle, selection for lower RFI could improve profitability. In this experiment, RFI was defined as the difference between an animal's actual feed intake and its expected feed intake, which was determined by regression of dry matter (DM) intake against mean body weight (BW) and growth rate. Nine hundred and three Holstein-Friesian heifer calves, aged between 5 and 7 mo, were measured for RFI in 3 cohorts of approximately 300 animals. Calves were housed under feedlot style conditions in groups of 15 to 20 for 85 to 95 d and had ad libitum access to a cubed alfalfa hay. Intakes of individual animals were recorded via an electronic feed recording system and BW gain was determined by weighing animals once or twice weekly, over a period of 60 to 70 d. Calves had DM intake (mean ± SD) of 8.3±1.37 kg of DM/d over the measurement period with BW gains of 1.1±0.17 kg/d. In terms of converting feed energy for maintenance and growth, the 10% most efficient calves (lowest RFI) ate 1.7 kg of DM less each day than the 10% least efficient calves (highest RFI) for the same rate of growth. Low-RFI heifers also had a significantly lower rate of intake (g/min) than high-RFI heifers. The heritability estimate of RFI (mean ± SE) was 0.27 (±0.12). These results indicate that substantial genetic variation in RFI exists, and that the magnitude of this variation is large enough to enable this trait to be considered as a candidate trait for future dairy breeding goals. A primary focus of future research should be to ensure that calves that are efficient at converting feed energy for maintenance and growth also become efficient at converting feed energy to milk. Future research will also be necessary to identify the consequences of selection for RFI on other traits (especially fertility and other fitness traits) and if any interactions exist between RFI and feeding level.
奶牛的饲料转化率是奶牛养殖盈利能力的一个重要组成部分，因为饲料成本占农场总支出的很大一部分。残留饲料摄入量（RFI）是衡量饲料转化率的一个有用指标，因为它可以用于比较在测量期间具有相同或不同生产水平的个体。如果奶牛的 RFI 存在遗传变异，那么选择较低的 RFI 可以提高盈利能力。在这项实验中，RFI 被定义为动物实际饲料摄入量与其预期饲料摄入量之间的差异，预期饲料摄入量是通过回归干物质（DM）摄入量与平均体重（BW）和生长速度来确定的。903 头荷斯坦-弗里森小母牛，年龄在 5 至 7 月龄之间，在 3 组约 300 头动物中测量了 RFI。小牛在饲料棚式条件下以每组 15 至 20 头的方式饲养 85 至 95 天，并可以自由采食切碎的紫花苜蓿干草。通过电子饲料记录系统记录个体动物的摄入量，通过每周称重动物一次或两次，在 60 至 70 天的时间内确定 BW 增益。在测量期间，小牛的 DM 摄入量（平均值±SD）为 8.3±1.37kg DM/d，BW 增益为 1.1±0.17kg/d。就饲料能量用于维持和生长而言，10%效率最高的小牛（RFI 最低）每天比 10%效率最低的小牛（RFI 最高）少吃 1.7kg DM，用于相同的生长速度。低 RFI 小母牛的摄入量（g/min）也明显低于高 RFI 小母牛。RFI 的遗传力估计值（平均值±SE）为 0.27（±0.12）。这些结果表明，RFI 存在大量遗传变异，而且这种变异的幅度足以使该性状被视为未来奶牛育种目标的候选性状。未来研究的主要重点应该是确保那些在维持和生长中有效利用饲料能量的小牛也能有效地将饲料能量转化为牛奶。未来的研究还需要确定对 RFI 的选择对其他性状（特别是繁殖力和其他健康性状）的影响，如果 RFI 与喂养水平之间存在任何相互作用。
