Graham D A, Clegg T A, O'Sullivan P, More S J
Animal Health Ireland, Main St., Carrick on Shannon, Co. Leitrim, Ireland.
UCD Centre for Veterinary Epidemiology and Risk Analysis, UCD School of Veterinary Medicine, University College Dublin, Belfield, Dublin 4, Ireland.
Prev Vet Med. 2015 Jul 1;120(3-4):298-305. doi: 10.1016/j.prevetmed.2015.04.019. Epub 2015 May 2.
This study was undertaken to investigate the impact of the retention of calves born in one calving season and considered to be persistently infected (PI) with bovine viral diarrhoea virus (BVDV) on herd-level outcomes in the following calving season. A secondary aim was to investigate the relationship between retention and the number of BVD+ calves detected the following season. The study population included a subset of herds enrolled in the 2012 voluntary BVD eradication programme in Ireland, specifically those with a birth registered to more than 80% of the cows between 1st January and 15th July and BVDV test results available for at least 80% of these calves, during both 2012 and 2013. Calves were considered PI based on either an initial positive result without further testing (BVDPOS) or a positive result on confirmatory testing (BVDPI), collectively considered BVD+ calves. Herd-level outcomes included the BVD status of the herd, and the number of BVD+ calves born between 1st January and 15th July 2013 (the study period). There was a significant univariable association between herd BVD status in 2013 and a number of general herd factors, including location, herd type, size and number of introduced animals (overall and those pregnant at time of introduction), as well as with each of six different factors related to the retention of virus-positive calves: the number of BVD+ calves in 2012; the maximum time (days) any one BVD+ born in 2012 was retained up to September 2013; the mean time (days) BVD+ animal(s) born in 2012 were retained up to September 2013; the date (quarter/year) the last BVD+ left the herd; the presence/number of 2012-born BVD+ retained in the herd at 1st January 2013. Separate multivariable models were constructed for each retention variable. The best model fit (based on AIC) was obtained using the retention variable "date (quarter/year) last BVD+ calf left the herd", followed by "total time all BVD+ calves were retained in the herd", with (log) herd size also retained in the models. Significant differences were also found in the number of positive calves detected in positive herds in 2013 for all of the calf retention risk factors. These findings confirm an increased probability of finding a BVD+ animal in a herd following the retention of positive calves born in the previous calving season, highlighting the importance of their prompt removal.
本研究旨在调查在一个产犊季节出生且被认为持续感染牛病毒性腹泻病毒（BVDV）的犊牛留养至下一个产犊季节对畜群水平结果的影响。第二个目的是研究留养与下一季检测到的BVD阳性犊牛数量之间的关系。研究群体包括爱尔兰2012年自愿性BVD根除计划中登记的一部分畜群，具体指那些在1月1日至7月15日期间，80%以上母牛有出生记录，且在2012年和2013年期间，至少80%的这些犊牛有BVDV检测结果的畜群。基于首次检测呈阳性且无需进一步检测（BVDPOS）或确认检测呈阳性（BVDPI），犊牛被视为持续感染，统称为BVD阳性犊牛。畜群水平结果包括畜群的BVD状态，以及2013年1月1日至7月15日（研究期）出生的BVD阳性犊牛数量。2013年畜群BVD状态与一些一般畜群因素之间存在显著的单变量关联，这些因素包括地点、畜群类型、规模以及引入动物的数量（总体数量以及引入时怀孕的数量），还与与病毒阳性犊牛留养相关的六个不同因素中的每一个有关：2012年BVD阳性犊牛的数量；2012年出生的任何一头BVD阳性犊牛留养至2013年9月的最长时间（天数）；2012年出生的BVD阳性动物留养至2013年9月的平均时间（天数）；最后一头BVD阳性动物离开畜群的日期（季度/年份）；2013年1月1日畜群中留养的2012年出生的BVD阳性动物的存在情况/数量。针对每个留养变量构建了单独的多变量模型。使用留养变量“最后一头BVD阳性犊牛离开畜群的日期（季度/年份）”获得了最佳模型拟合（基于AIC），其次是“所有BVD阳性犊牛在畜群中留养的总时间”，模型中还保留了（对数）畜群规模。对于所有犊牛留养风险因素，2013年在阳性畜群中检测到的阳性犊牛数量也存在显著差异。这些发现证实，在前一个产犊季节出生的阳性犊牛留养后，畜群中发现BVD阳性动物的概率增加，突出了及时清除它们的重要性。
