Macdonald K A, Pryce J E, Spelman R J, Davis S R, Wales W J, Waghorn G C, Williams Y J, Marett L C, Hayes B J
DairyNZ, Hamilton 3240, New Zealand.
Biosciences Research Division, Department of Environment and Primary Industries Victoria, Bundoora, VIC 3083, Australia; Dairy Futures Cooperative Research Centre, Bundoora, VIC 3083, Australia.
J Dairy Sci. 2014 Mar;97(3):1427-35. doi: 10.3168/jds.2013-7227. Epub 2013 Dec 28.
Residual feed intake (RFI), as a measure of feed conversion during growth, was estimated for around 2,000 growing Holstein-Friesian heifer calves aged 6 to 9 mo in New Zealand and Australia, and individuals from the most and least efficient deciles (low and high RFI phenotypes) were retained. These animals (78 New Zealand cows, 105 Australian cows) were reevaluated during their first lactation to determine if divergence for RFI observed during growth was maintained during lactation. Mean daily body weight (BW) gain during assessment as calves had been 0.86 and 1.15 kg for the respective countries, and the divergence in RFI between most and least efficient deciles for growth was 21% (1.39 and 1.42 kg of dry matter, for New Zealand and Australia, respectively). At the commencement of evaluation during lactation, the cows were aged 26 to 29 mo. All were fed alfalfa and grass cubes; it was the sole diet in New Zealand, whereas 6 kg of crushed wheat/d was also fed in Australia. Measurements of RFI during lactation occurred for 34 to 37 d with measurements of milk production (daily), milk composition (2 to 3 times per week), BW and BW change (1 to 3 times per week), as well as body condition score (BCS). Daily milk production averaged 13.8 kg for New Zealand cows and 20.0 kg in Australia. No statistically significant differences were observed between calf RFI decile groups for dry matter intake, milk production, BW change, or BCS; however a significant difference was noted between groups for lactating RFI. Residual feed intake was about 3% lower for lactating cows identified as most efficient as growing calves, and no negative effects on production were observed. These results support the hypothesis that calves divergent for RFI during growth are also divergent for RFI when lactating. The causes for this reduced divergence need to be investigated to ensure that genetic selection programs based on low RFI (better efficiency) are robust.
在新西兰和澳大利亚，对约2000头6至9月龄生长阶段的荷斯坦-弗里生小母牛犊的剩余采食量（RFI）进行了评估，RFI是衡量生长期间饲料转化率的指标。保留了来自最高效和最低效十分位数组（低RFI和高RFI表型）的个体。这些动物（78头新西兰奶牛、105头澳大利亚奶牛）在首次泌乳期间重新进行了评估，以确定生长期间观察到的RFI差异在泌乳期间是否得以维持。犊牛阶段评估期间的平均日体重（BW）增加量，新西兰和澳大利亚分别为0.86和1.15千克，生长阶段最高效和最低效十分位数组之间的RFI差异为21%（新西兰和澳大利亚分别为1.39和1.42千克干物质）。泌乳期评估开始时，奶牛年龄为26至29月龄。所有奶牛均饲喂苜蓿和草块；在新西兰这是唯一的日粮，而在澳大利亚还额外饲喂6千克/天的碎小麦。泌乳期RFI的测量持续34至37天，同时测量产奶量（每日）、乳成分（每周2至3次）、BW及BW变化（每周1至3次）以及体况评分（BCS）。新西兰奶牛的日均产奶量平均为13.8千克，澳大利亚为20.0千克。在犊牛RFI十分位数组之间，干物质采食量、产奶量、BW变化或BCS未观察到统计学上的显著差异；然而，泌乳期RFI在组间存在显著差异。作为犊牛时确定为最高效的泌乳奶牛，其剩余采食量约低3%，且未观察到对生产的负面影响。这些结果支持以下假设：生长期间RFI存在差异的犊牛在泌乳时RFI也存在差异。需要对这种差异减小的原因进行调查，以确保基于低RFI（更高效率）的遗传选择计划的稳健性。
