Many research groups have developed mathematical models to simulate the dynamics of BVDV infections in cattle herds. However, most models use estimates for within-herd BVDV transmission rates that are either based on expert opinion or adapted from other dairy herd simulation models presented in the literature. There is currently little information on the transmission rates for BVDV in extensively grazed beef herds partly due to the logistical challenges in obtaining longitudinal data of individual animal’s seroconversion, and it may not be appropriate to apply the same transmission rates from intensive dairy herds given the significant differences in herd demographics and management. To address this knowledge gap, we measured BVDV antibody levels in 15 replacement heifers in each of 75 New Zealand beef breeding farms after their first calving and again at pregnancy scanning or weaning to check for seroconversion. Among these, data from 9 farms were used to infer the within-herd BVDV transmission rate with an approximate Bayesian computation method. The most probable within-herd BVDV transmission rate was estimated as 0.11 per persistently infected (PI) animal per day with a 95% highest posterior density interval between 0.03 and 0.34. This suggests that BVDV transmission in extensively grazed beef herds is generally slower than in dairy herds where the transmission rate has been estimated at 0.50 per PI animal per day and therefore may not be sufficient to ensure that all susceptible breeding females gain adequate immunity to the virus before the risk period of early pregnancy for generating new PI calves.

中文翻译：

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广泛放牧的肉牛群中牛病毒性腹泻病毒的牛群内传播率估算

许多研究小组已经开发出数学模型来模拟牛群中BVDV感染的动态。但是，大多数模型都使用基于专家意见的牛群内BVDV传输速率的估计值，或根据文献中介绍的其他奶牛群模拟模型改编而成的估计值。目前，关于广泛吃草的牛群中BVDV传播速率的信息很少，部分原因是在获取单个动物血清转化的纵向数据方面存在逻辑上的挑战，鉴于集约化的显着性，使用集约化奶牛群的相同传播速率可能并不适当。群体人口统计和管理方面的差异。为了弥补这一知识鸿沟，我们对75个新西兰牛肉育种场中的15个替换母牛进行了第一次产犊，然后再次进行妊娠扫描或断奶以检查血清转化，以测量BVDV抗体水平。其中，来自9个农场的数据被用于通过近似贝叶斯计算方法推断群内BVDV的传输速率。据估计，最可能的牛群内部BVDV传播速率为每只持续感染（PI）动物每天0.11只，其后密度最高间隔在0.03和0.34之间为95％。这表明，在广泛放牧的牛群中，BVDV的传播通常要慢于乳牛群，后者的传播率估计为0。