Department of Veterinary Sciences, Texas Tech University, Lubbock 79415.
Department of Veterinary Population Medicine, University of Minnesota, St. Paul 55108.
J Dairy Sci. 2021 Feb;104(2):2140-2150. doi: 10.3168/jds.2020-19153. Epub 2020 Dec 11.
It is well established that subclinical mastitis (SCM), characterized by somatic cell count (SCC) >200,000 cells/mL, has a negative effect on the productivity, reproductive performance, and survivability of cows from conventional dairy herds. However, in organic herds, where the use of antimicrobial drugs is restricted for the treatment and control of intramammary infections (IMI) in dairy cows, little is known about the effect of SCM on performance and survivability. The objective of this study was to evaluate whether SCM diagnosed during the first month of lactation was associated with SCC linear score dynamics, milk production, fertility, and culling of dairy cows in USDA-certified organic herds. We collected data from 2 organic herds in New Mexico and Texas. A total of 1,511 cows that calved between June 2018 and May 2019 were included in the study and were followed until month 10 of the current lactation. Cows with SCC >200,000 cells/mL in the first month of lactation were considered to have SCM. We used mixed linear regression models accounting for repeated measures to assess the effect of SCM on monthly milk production and SCC linear scores. We used Cox proportional hazards models to evaluate the effect of SCM on the risk of pregnancy and culling. We considered parity, farm, previous gestation length, stillbirth, twinning, dystocia, and 2- and 3-way interactions as potential confounders. Cows diagnosed with SCM during the first month of lactation produced less milk than cows without SCM. Cows with SCM had elevated SCC linear scores during their previous lactation and throughout the subsequent months of lactation compared to cows without SCM. The effect of SCM on SCC linear scores was more pronounced in multiparous than primiparous cows. Subclinical mastitis during the first month of lactation did not affect the likelihood of pregnancy during the first 300 d in milk. Cows with SCM in the first month were more likely to die or be culled during the 300 d of lactation than cows without SCM. We observed that elevated SCC in the first month of lactation had detrimental effects on the milk yield and survivability of dairy cows in USDA organic herds, but it did not affect reproductive performance. We demonstrated that cows with SCM diagnosed in the first month of lactation continued to have elevated SCC linear scores throughout their entire lactation, and that elevated SCC was carried over from the previous lactation.
已证实，亚临床乳腺炎（SCM）的特征是体细胞计数（SCC）>200,000 个细胞/mL，这对常规奶牛场奶牛的生产力、繁殖性能和存活率有负面影响。然而，在有机牛群中，由于限制了用于治疗和控制奶牛乳腺炎的抗菌药物的使用，因此对于 SCM 对性能和存活率的影响知之甚少。本研究的目的是评估泌乳早期诊断的 SCM 是否与 SCC 线性评分动态、产奶量、奶牛的繁殖力和淘汰有关。我们从新墨西哥州和德克萨斯州的 2 个有机牛群中收集数据。共纳入了 2018 年 6 月至 2019 年 5 月间分娩的 1511 头奶牛，并在当前泌乳期的第 10 个月进行跟踪。泌乳第 1 个月 SCC>200,000 个细胞/mL 的奶牛被认为患有 SCM。我们使用混合线性回归模型，考虑到重复测量，评估 SCM 对每月产奶量和 SCC 线性评分的影响。我们使用 Cox 比例风险模型评估 SCM 对怀孕和淘汰风险的影响。我们认为胎次、农场、上次妊娠长度、死胎、双胞胎、难产以及 2 因素和 3 因素交互作用是潜在的混杂因素。泌乳早期诊断为 SCM 的奶牛比没有 SCM 的奶牛产奶量少。与没有 SCM 的奶牛相比，患有 SCM 的奶牛在上一次泌乳期和随后的泌乳月份中 SCC 线性评分较高。SCM 对 SCC 线性评分的影响在经产牛中比初产牛更为明显。泌乳早期的亚临床乳腺炎不会影响泌乳前 300 天的怀孕几率。泌乳第 1 个月患有 SCM 的奶牛在泌乳 300 天内死亡或淘汰的可能性高于没有 SCM 的奶牛。我们观察到，USDA 有机牛群中泌乳早期 SCC 升高对奶牛的产奶量和存活率有不利影响，但对繁殖性能没有影响。我们证明，在泌乳早期诊断为 SCM 的奶牛在整个泌乳期内 SCC 线性评分持续升高，并且 SCC 从上一次泌乳期升高。
