Archer S C
School of Veterinary Medicine, University of Surrey, Guildford, Surrey GU2 7AL, United Kingdom.
JDS Commun. 2021 May 21;2(5):248-252. doi: 10.3168/jdsc.2020-0068. eCollection 2021 Sep.
This study estimates the birth weight and growth rate for UK dairy calves and partitions unexplained variability in the weight of calves aged up to 20 wk. Raising replacements is a major contributor to the sustainability of dairying, but existing industry targets may not be applicable and achievable on all farms. For hierarchical data, variance partition coefficients (VPC) describe the proportion of unexplained variance residing at each level of the hierarchy due to clustering and indicate the potential to change outcomes through influencing variables acting at each level. This information could be used to inform the allocation of resources for further investigation. Calves were weighed according to farm-specific protocols. The data set analyzed contained records between June 5, 2014, and February 28, 2020, from 28 veterinary practices servicing 139 farms with 19,708 calves up to 20 wk of age, from which there were 59,588 weight recordings. Calves were Holstein-Friesian females. Calf weight was described using a multivariable mixed linear model with fixed effects for age. Mean birth weight was 41 kg. Mean growth rate increased from 0.59 kg/d at 1 d of age to 0.87 kg/d after 138 d. Cumulative mean growth rate up to 138 d of age was 0.73 kg/d. Birth weight and growth rate estimates are comparable with those made previously but are more precise due to larger sample size. Calf growth rate varied between farms, meaning that VPC at the calf, farm, and veterinary practice levels depended on calf age. Most unexplained variation in the weight of calves aged 66 d and over was due to differences between farms. At birth and 130 d of age, VPC at the farm level was 0.02 and 0.77, respectively. In contrast, most variation in neonatal calf weight was due to differences between calves. At birth and 130 d of age, VPC at the calf level was 0.84 and 0.20, respectively. The 0.025 to 0.975 quantile coverage of cluster-specific mean calf birth weight for combinations of veterinary practice and farm was 34 to 49 kg. The 0.025 to 0.975 quantile coverage of cluster-specific cumulative mean calf growth rate for combinations of veterinary practice and farm was 0.56 to 1.00 kg/d. Understanding reasons for these differences should be the basis of research into optimal calf management strategies to define economic targets for specific circumstances.
本研究估算了英国奶牛犊牛的出生体重和生长速率，并对20周龄以内犊牛体重中无法解释的变异性进行了划分。培育后备母牛是奶牛业可持续发展的一个主要因素，但现有的行业目标可能并非适用于所有农场，也并非所有农场都能实现。对于分层数据，方差划分系数（VPC）描述了由于聚类而在层次结构的每个级别上存在的无法解释的方差比例，并表明通过影响在每个级别上起作用的变量来改变结果的可能性。这些信息可用于为进一步调查的资源分配提供依据。犊牛按照农场特定的方案进行称重。分析的数据集包含2014年6月5日至2020年2月28日期间的数据，来自为139个农场服务的28家兽医诊所，涉及19708头20周龄以内的犊牛，共有59588次体重记录。犊牛为荷斯坦-弗里生雌性。使用具有年龄固定效应的多变量混合线性模型来描述犊牛体重。平均出生体重为41千克。平均生长速率从1日龄时的0.59千克/天增加到138天后的0.87千克/天。至138日龄的累积平均生长速率为0.73千克/天。出生体重和生长速率的估算值与之前的估算值具有可比性，但由于样本量更大，所以更为精确。犊牛生长速率在不同农场之间存在差异，这意味着犊牛、农场和兽医诊所层面的VPC取决于犊牛年龄。66日龄及以上犊牛体重中，大多数无法解释的变异是由于农场之间的差异。在出生时和130日龄时，农场层面的VPC分别为0.02和0.77。相比之下，新生犊牛体重的大多数变异是由于犊牛之间的差异。在出生时和130日龄时，犊牛层面的VPC分别为0.84和0.20。兽医诊所和农场组合的特定聚类平均犊牛出生体重的0.025至0.975分位数范围为34至49千克。兽医诊所和农场组合的特定聚类累积平均犊牛生长速率的0.025至0.975分位数范围为0.56至1.00千克/天。了解这些差异的原因应成为研究最佳犊牛管理策略的基础，以便为特定情况确定经济目标。
