Bovine Functional Genomics Laboratory, Agricultural Research Service, USDA, Beltsville, MD 20705, USA.
J Anim Sci. 2013 Aug;91(8):3978-88. doi: 10.2527/jas.2012-5977. Epub 2013 May 8.
Improved feed efficiency is a primary goal in dairy production to reduce feed costs and negative impacts of production on the environment. Estimates for efficiency of feed conversion to milk production based on residual feed intake (RFI) in dairy cattle are limited, primarily due to a lack of individual feed intake measurements for lactating cows. Feed intake was measured in Holstein cows during the first 90 d of lactation to estimate the heritability and repeatability of RFI, minimum test duration for evaluating RFI in early lactation, and its association with other production traits. Data were obtained from 453 lactations (214 heifers and 239 multiparous cows) from 292 individual cows from September 2007 to December 2011. Cows were housed in a free-stall barn and monitored for individual daily feed consumption using the GrowSafe 4000 System (GrowSafe Systems, Ltd., Airdrie, AB, Canada). Animals were fed a total mixed ration 3 times daily, milked twice daily, and weighed every 10 to 14 d. Milk yield was measured at each milking. Feed DM percentage was measured daily, and nutrient composition was analyzed from a weekly composite. Milk composition was analyzed weekly, alternating between morning and evening milking periods. Estimates of RFI were determined as the difference between actual energy intake and predicted intake based on a linear model with fixed effects of parity (1, 2, ≥ 3) and regressions on metabolic BW, ADG, and energy-corrected milk yield. Heritability was estimated to be moderate (0.36 ± 0.06), and repeatability was estimated at 0.56 across lactations. A test period through 53 d in milk (DIM) explained 81% of the variation provided by a test through 90 DIM. Multiple regression analysis indicated that high efficiency was associated with less time feeding per day and slower feeding rate, which may contribute to differences in RFI among cows. The heritability and repeatability of RFI suggest an opportunity to improve feed efficiency through genetic selection, which could reduce feed costs, manure output, and greenhouse gas emissions associated with dairy production.
提高饲料效率是奶牛生产的主要目标，以降低饲料成本和生产对环境的负面影响。基于奶牛残留采食量（RFI）估计饲料转化为牛奶的效率是有限的，主要是因为缺乏泌乳牛个体饲料采食量的测量。在泌乳的前 90 d 期间，对荷斯坦奶牛的饲料采食量进行了测量，以估计 RFI 的遗传力和可重复性、评估早期泌乳期 RFI 的最小测试持续时间及其与其他生产性状的关系。数据来自于 2007 年 9 月至 2011 年 12 月期间 292 头奶牛的 453 个泌乳期（214 头小母牛和 239 头经产牛）。奶牛被安置在一个自由式畜栏中，使用 GrowSafe 4000 系统（GrowSafe Systems，Ltd.，Airdrie，AB，加拿大）对个体每日饲料采食量进行监测。动物每天喂食三次，每天挤奶两次，并每 10-14 d 称重一次。每次挤奶时都测量产奶量。每天测量饲料 DM 百分比，并每周对混合饲料进行一次营养成分分析。每周交替分析早晚挤奶期间的牛奶成分。RFI 的估计值是根据线性模型确定的，该模型具有胎次（1、2、≥3）的固定效应和代谢 BW、ADG 和能量校正乳产量的回归，实际能量摄入量与预测摄入量之间的差异。遗传力估计为中等（0.36 ± 0.06），泌乳期内的可重复性估计为 0.56。在 53 d 泌乳期（DIM）内的测试期解释了 90 DIM 内测试期提供的 81%的变异。多元回归分析表明，高效率与每天进食时间较短和进食速度较慢有关，这可能是奶牛之间 RFI 差异的原因。RFI 的遗传力和可重复性表明有机会通过遗传选择提高饲料效率，这可以降低饲料成本、粪便产出和与奶牛生产相关的温室气体排放。
