Department of Animal Science, University of California, Davis 95616.
Cooperative Extension, Division of Agriculture and Natural Resources, University of California, Orland 95963.
J Dairy Sci. 2019 Aug;102(8):7320-7328. doi: 10.3168/jds.2018-15463. Epub 2019 Jun 13.
Mortality in preweaned dairy calves is a significant source of economic loss for dairy producers. In particular, bovine respiratory disease (BRD) is a leading cause of death in preweaned dairy calves. The objectives of this study were to investigate management practices and their effects on mortality, both that specifically attributed to BRD and overall mortality due to all causes, in preweaned dairy calves. Rates of failure of passive transfer of immunity (FPT) are also reported. The study consisted of a convenience sample of 5 dairies across California, selected based on management practices, calf records, location, and size. Trained study personnel performed comprehensive calf management surveys on every dairy at least once every season. Calves were enrolled in the study at birth and followed until weaning. Mixed-effect logistic regression models were specified for the outcomes all-cause mortality (any death before weaning) and mortality attributed to BRD. The 2 final models included a total of 11,470 calves that were born on the study dairies and followed until weaning. The study cohort's overall crude mortality was 2.8%, with crude mortality of individual dairies ranging from 1.7 to 7.2%. The proportion of mortality attributed to BRD was 19.3%, with a range of 0 to 27.1% on the study dairies. Increasing the frequency of changing maternity pen bedding was associated with a decreased risk of mortality due to BRD. Calves diagnosed with BRD in the spring had an increased risk of mortality compared with calves born in the summer; mortality in calves with fall and winter BRD diagnoses did not different significantly from that in summer. Season of mortality was not significant in either model. Feeding ≥5.7 L of milk per day per calf (vs. ≤3.7 L/d) decreased the risk of mortality in calves over 21 d of age. Twins had a 68% increased risk of all-cause mortality compared with calves born as singletons. Both mortality models showed an association between administration of a modified live vaccine in dams (targeting BRD pathogens) and a decreased risk of mortality in calves. Using a serum total protein cut-off of 5.2 g/dL, 16.8% of calves had FPT, with a mean serum total protein concentration of 5.94 ± 0.06 g/dL across all calves sampled.
在哺乳期前的奶牛犊牛中,死亡率是奶农经济损失的主要原因。特别是,牛呼吸道疾病(BRD)是哺乳期前奶牛犊牛死亡的主要原因。本研究的目的是调查管理实践及其对死亡率的影响,包括专门归因于 BRD 的死亡率和因各种原因导致的总死亡率。同时也报告了被动免疫失败率(FPT)。该研究是在加利福尼亚州的 5 个奶牛场进行的,这些奶牛场是根据管理实践、小牛记录、位置和规模选择的。经过培训的研究人员至少每季度对每个奶牛场进行一次全面的小牛管理调查。小牛在出生时即被纳入研究,并一直跟踪至断奶。使用混合效应逻辑回归模型来确定所有原因死亡率(断奶前的任何死亡)和归因于 BRD 的死亡率这两个结果。最终的 2 个模型共包括了在研究奶牛场出生并跟踪至断奶的 11470 头小牛。研究队列的总死亡率为 2.8%,个别奶牛场的死亡率范围为 1.7%至 7.2%。归因于 BRD 的死亡率比例为 19.3%,研究奶牛场的死亡率范围为 0%至 27.1%。增加产房垫料更换的频率与降低 BRD 相关死亡率的风险有关。在春季被诊断患有 BRD 的小牛与在夏季出生的小牛相比,死亡率更高;而在秋季和冬季被诊断患有 BRD 的小牛的死亡率与夏季出生的小牛相比没有显著差异。在这两个模型中,死亡率季节均不显著。每天每头小牛喂养≥5.7 升牛奶(vs. ≤3.7 升/天)可降低 21 日龄以上小牛的死亡率。与单胎出生的小牛相比,双胞胎的全因死亡率增加了 68%。两个死亡率模型都显示,在母体中使用活疫苗(针对 BRD 病原体)与降低小牛死亡率之间存在关联。使用血清总蛋白截止值 5.2 g/dL,16.8%的小牛存在 FPT,所有采样小牛的血清总蛋白浓度平均值为 5.94 ± 0.06 g/dL。