Chiozza-LogronoJ Lameness Grazing Dairy Cows

Lameness in Early Lactation is Associated with Lower Productive and Reproductive Performance in a Herd of Supplemented Grazing Dairy Cows The main aim of this study was to assess the associations between the timing of lameness clinical case occurrence in lactation with productive and reproductive performances in grazing Holstein cows. A cohort study was carried out on a dataset with records from a commercial dairy herd (Buenos Aires, Argentina) for cows that calved and were dried off from January 2010 through June 2017. The first recorded event of lameness per lactation was considered for the study. Criteria for lactation inclusion included not having uterine diseases, mastitis, or anovulatory cysts during the studied risk period (i.e., up to 200 DIM). Therefore, a total of 7156 out of 20,086 lactations were included in the statistical analysis. The association between lameness case occurrence in lactation (cows not lame (LG0) vs. lame cows between parturition and first service (LG1) vs. lame cows between first service and first pregnancy (LG2)) with productive (i.e., accumulated milk yield to 150 DIM (MILK150) and 300 DIM (MILK305)) and reproductive performances (hazard of insemi-nation and pregnancy) was analyzed with linear regression models and proportional hazard re-gression models, respectively. Lame cows produced 161 and 183 kg less MILK150 and MILK305 than non-lame herd mates, respectively. Moreover, LG1 cows produced 216 kg less MILK150 and 200 kg less MILK305 than LG0 cows, and LG2 cows also produced 58 kg less MILK150 and 158 kg less MILK305 than LG0 cows. The LG1 cows had a lower hazard of service than LG0 cows (HR = 0.43, 95%CI = 0.39–0.47). Furthermore, LG1 cows had a lower hazard of pregnancy than LG0 cows (HR = 0.52, 95%CI = 0.46–0.59) and took longer to get pregnant than LG0 cows (median [95%CI], 139 [132–144] vs. 101 [99–103]). Moreover, LG2 cows had a much lower hazard of pregnancy than LG0 cows (HR = 0.08, 95%CI = 0.05–0.12) and much longer calving to first pregnancy interval than LG0 cows (188 [183–196] vs. 101 [99–103]). In conclusion, cows that become lame in early lactation produce less milk and have lower hazards of insemination and pregnancy than herd mates that are healthy or become lame later in lactation. In addition, cows that become lame immediately after the voluntarily waiting period have the poorest reproductive performance (i.e., they have the lowest hazard of pregnancy and the longest calving to pregnancy interval).

泌乳早期跛行与补饲放牧荷斯坦奶牛（Holstein）群的生产及繁殖性能降低相关
本研究旨在评估泌乳期跛行临床病例的发生时机与放牧荷斯坦奶牛的生产及繁殖性能之间的关联。本研究针对阿根廷布宜诺斯艾利斯某商业奶牛场2010年1月至2017年6月期间产犊并完成干奶的奶牛数据集开展队列研究，共纳入20086个泌乳周期，最终筛选出7156个符合标准的泌乳周期用于统计分析。
泌乳周期的纳入标准为：在研究风险期（即泌乳前200天，泌乳天数（Days in Milk, DIM））内未患子宫疾病、乳腺炎或无排卵囊肿。本研究以每个泌乳周期首次记录的跛行事件作为分析依据，并将受试奶牛按跛行发生时段分为三组：无跛行奶牛组（LG0）、分娩至首次配种期间跛行奶牛组（LG1）、首次配种至首次妊娠期间跛行奶牛组（LG2）。
随后分别采用线性回归模型与比例风险回归模型，分析跛行发生与生产性能、繁殖性能的关联：其中生产性能指标为泌乳150天累计产奶量（MILK150）与泌乳305天累计产奶量（MILK305），繁殖性能指标为配种风险与妊娠风险。
结果显示，整体跛行奶牛的MILK150与MILK305分别较无跛行同群奶牛低161kg和183kg。其中LG1组奶牛的MILK150和MILK305较LG0组分别低216kg和200kg；LG2组奶牛的MILK150和MILK305较LG0组分别低58kg和158kg。LG1组奶牛的配种风险低于LG0组（风险比（Hazard Ratio, HR）=0.43，95%置信区间（Confidence Interval, CI）=0.39–0.47）。此外，LG1组奶牛的妊娠风险低于LG0组（HR=0.52，95%CI=0.46–0.59），且妊娠所需时长较LG0组更长（中位数[95%CI]：139[132–144] vs. 101[99–103]）。LG2组奶牛的妊娠风险远低于LG0组（HR=0.08，95%CI=0.05–0.12），且从分娩至首次妊娠的间隔时长较LG0组显著更长（188[183–196] vs. 101[99–103]）。
综上，泌乳早期出现跛行的奶牛较健康奶牛或泌乳后期跛行的同群同伴产奶量更低，配种与妊娠风险也更低。此外，自愿等待期后立即出现跛行的奶牛（即LG1组）繁殖性能最差，具体表现为妊娠风险最低且分娩至妊娠的间隔时长最长。