Data for: A longitudinal study of the dynamics of Mycoplasma bovis antibody status in primiparous cows and bulk tank milk in Swedish dairy herds

In this study the aims were: (1) to monitor the changes in M. bovis antibody status in BTM and milk from PP cows in Swedish dairy herds over time, and (2) to investigate potential risk factors and herd health variables associated with M. bovis antibodies in primiparous cows. Study population Five regions in the south of Sweden with previously knowned cases of M. bovis were selected for the study. Dairy herds from these regions with an average of more than 70 cows (both lactating and dry) on a yearly basis and affiliated to the Dairy Herd Improvement (DHI) database (Växa Sverige) were invited to participate in the study. 139 herds accepted and ten herds joined later due to contact with infected herds or diagnosing Mycoplasma bovis at the herd. In total, 143 herds were used in the statistical analysis, six herds had no samples from primiparous cows and were dropped. Sampling Herds were sampled four times with approximately six-month intervals, in (1) September 2019, (2) February 2020, (3) November 2020 and (4) May 2021, with a two-month long sampling window each time. For each herd, on each sampling occasion, milk samples were collected from the three youngest home-bred PP cows and BTM. Data Herd-level data on health and production variables were retrieved from the Dairy Herd Improvement database, Växa Sverige. The data were aggregated in four 12-month periods calculated backwards from the start of each sampling period, (1) 2019-09-01, (2) 2020-02-01, (3) 2020-11-01 and (4) 2021-05-01. Data regarding mortality, culling rates, reproductive performance, and veterinary-reported clinical diseases were calculated as cases per 100 animals at risk. Breed was classified into four categories on herd level, the main breed constituting more than 80% of the cows. Herd-level data in 12-month periods regarding herd size (i.e., number of female animals >24 months old), number of introduced cattle, median age of introduced cattle, and number of herds the introduced cattle were received from (inherds) were collected from the National Cattle Database (Swedish Board of Agriculture 2022). Data on herd size (number of milking cows) in fifteen herds not affiliated with the DHI were retrieved from a questionnaire answered by these farmers during autumn 2020.本研究旨在达成两项研究目标：(1) 长期监测瑞典奶牛群中奶罐混合乳（bulk tank milk，BTM）与头胎奶牛（primiparous cows）乳汁内牛支原体（Mycoplasma bovis，M. bovis）抗体水平的动态变化；(2) 探究与头胎奶牛牛支原体抗体水平相关的潜在风险因素及牛群健康相关变量。 **研究群体** 本研究选取瑞典南部5个既往存在牛支原体感染病例的区域作为研究区域。从上述区域中，筛选出年平均存栏量（含泌乳牛与干奶牛）超过70头、且隶属于奶牛改良计划（Dairy Herd Improvement，DHI）数据库（Växa Sverige）的奶牛场，邀请其参与本研究。最终共有139家奶牛场同意参与，另有10家奶牛场因接触感染牛群或场内确诊牛支原体感染，于后续加入本研究。本研究最终纳入143家奶牛场用于统计学分析，另有6家未采集到头胎奶牛样本的奶牛场被排除。 **采样方案** 各奶牛场共接受4次采样，采样间隔约为6个月，分别为(1)2019年9月、(2)2020年2月、(3)2020年11月及(4)2021年5月，每次采样均设置为期2个月的采样窗口期。每次采样时，各奶牛场均从场内繁育的3头最年轻的头胎奶牛以及奶罐混合乳中采集乳汁样本。 **数据采集** 牛群层面的健康与生产变量数据均从奶牛改良计划数据库Växa Sverige获取。数据以各采样周期起始日为基准向后回溯，划分为4个12个月的统计时段，分别为(1)2019-09-01、(2)2020-02-01、(3)2020-11-01及(4)2021-05-01。死亡率、淘汰率、繁殖性能以及兽医上报的临床疾病数据均以每100头易感动物的发病数为单位进行计算。牛群层面的品种被划分为4个类别，其中主养品种的存栏占比需超过全场奶牛总数的80%。12个月统计时段内的牛群层面数据，包括牛群规模（即24月龄以上雌性动物数量）、引进牛只数量、引进牛只的中位年龄以及引进牛只的来源场数量（inherds），均从国家牛只数据库（瑞典农业局2022）获取。对于15家未加入奶牛改良计划数据库的奶牛场，其泌乳牛存栏规模数据通过2020年秋季由场主填写的调查问卷获取。