Associations of somatic cell count with milk yield and reproductive performance in grazing dairy cows

Poor udder health status can have a detrimental effect on milk yield and reproductive performance leading to reductions in the dairy farm profit. The objective of this retrospective longitudinal study was to assess the associations of somatic cell count (SCC) with daily milk yield and reproductive performance. A database having 1,930,376 lactations from 867 Argentinean grazing dairy herds records collected for 15 years was used. The association of the evolution of SCC (healthy vs. new case vs. cured vs. chronic; with 150,000 SCC/mL as threshold) and of the severity of SCC [mild (150,000 to 400,000 SCC/mL) vs. moderate (400,000 to 1,000,000 SCC/mL) vs. severe (>1,000,000 SCC/mL)] with the odds for conception were estimated. Also, the insemination rate by 200 DIM was estimated depending on SCC category (<150K or >150K), included as a time-dependent variable in Cox regression analysis. Finally, the associations of the linear score of SCC (LS-SCC) with daily milk yield were estimated depending on parity and milk production quartile乳房健康状况不佳会对产奶量与繁殖性能产生不利影响，进而降低奶牛养殖场的经营利润。本回顾性纵向研究旨在探究体细胞计数（Somatic Cell Count, SCC）与日产奶量及繁殖性能之间的相关性。本研究使用了一个收集周期长达15年的数据库，该数据库涵盖了来自867个阿根廷放牧型奶牛牧场的共计1,930,376条泌乳记录。研究评估了体细胞计数的变化状态（以150,000 SCC/mL为阈值，分为健康、新发感染、已治愈、慢性感染四类）以及体细胞计数严重程度（轻度：150,000~400,000 SCC/mL；中度：400,000~1,000,000 SCC/mL；重度：>1,000,000 SCC/mL）与受孕比值比之间的相关性。此外，本研究以体细胞计数类别（<150K或>150K）作为时依变量纳入Cox回归分析，评估了泌乳第200天（Days In Milk, DIM）的授精率。最后，本研究基于胎次与产奶量四分位数分组，评估了体细胞线性评分（Linear Score of SCC, LS-SCC）与日产奶量之间的相关性。