Department of Large Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, 736 Wilson Rd, East Lansing, MI 48895, United States.
Department of Large Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, 736 Wilson Rd, East Lansing, MI 48895, United States.
Prev Vet Med. 2020 Aug;181:105055. doi: 10.1016/j.prevetmed.2020.105055. Epub 2020 Jun 9.
Bovine leukosis is a chronic lymphoproliferative disorder caused by bovine leukemia virus (BLV). Previous studies estimate that 38 % of cow-calf beef herds and 10.3 % of individual beef cows in the US are BLV seropositive. About 70 % of BLV infected animals are asymptomatic carriers of the virus, while less than 5% develop lymphosarcoma, the leading reason for carcass condemnation at the US slaughterhouses. Studies provide evidence that BLV infection leads to decreased immune function making animals more vulnerable to other diseases, which could shorten their productive lifespan and increase economic losses in the cattle industry. BLV seropositive dairy cows are reportedly more likely to be culled sooner compared with their uninfected herd mates. Beyond simple prevalence studies, little is known about the impact of BLV infection in beef cattle production or specifically on beef cow longevity. Our objective was to determine the association between BLV infection and cow longevity in beef cow-calf operations. Twenty-seven cow-calf herds from the Upper Midwest volunteered to participate in this study. Female beef cattle (n = 3146) were tested for serum BLV antibodies by ELISA. A subsample of 648 cows were also tested for BLV proviral load (PVL). Culling data was collected for the subsequent 24 months. Twenty-one herds (77.7 %) had at least one BLV-infected animal, and 29.2 % (930/3146) of tested animals were BLV seropositive. Of the BLV-positive cows, 33.7 % (318/943) were culled compared with 32.1 % (541/1682) of the seronegative cows. BLV status did not affect cows' longevity within herds (P = 0.062). However, cows with high BLV PVL had decreased survival within the herd compared with ELISA- negative cows (P = 0.01). Overall, infection with BLV did not impact beef cow longevity unless the disease had progressed to a point of high BLV PVL.
牛白血病是一种由牛白血病病毒（BLV）引起的慢性淋巴增生性疾病。先前的研究估计，美国 38%的奶牛-小牛牛肉群和 10.3%的个体奶牛为 BLV 血清阳性。大约 70%的 BLV 感染动物是该病毒的无症状携带者，而不到 5%的动物会发展为淋巴肉瘤，这是美国屠宰场进行屠体废弃的主要原因。研究提供的证据表明，BLV 感染会导致免疫功能下降，使动物更容易感染其他疾病，从而缩短其生产寿命并增加牛群的经济损失。据报道，BLV 血清阳性奶牛比未感染的同群奶牛更早被淘汰。除了简单的流行率研究外，人们对 BLV 感染对肉牛生产的影响或对奶牛牛长寿的具体影响知之甚少。我们的目标是确定 BLV 感染与肉牛牛长寿之间的关系。来自中西部上地区的 27 个奶牛-小牛牛群自愿参与了这项研究。通过 ELISA 检测血清 BLV 抗体，对 3146 头雌性肉牛进行了检测。还对 648 头奶牛进行了 BLV 前病毒载量（PVL）的亚群检测。在随后的 24 个月内收集淘汰数据。21 个牛群（77.7%）至少有一头 BLV 感染动物，29.2%（930/3146）的检测动物为 BLV 血清阳性。在 BLV 阳性牛中，与血清阴性牛（541/1682）相比，有 33.7%（318/943）的牛被淘汰。BLV 状态对牛群内的牛的寿命没有影响（P=0.062）。然而，与 ELISA 阴性牛相比，高 BLV PVL 的牛在牛群内的存活率降低（P=0.01）。总的来说，除非疾病进展到 BLV PVL 很高的程度，否则 BLV 感染不会影响肉牛的寿命。
