Abstract
Bovine leukaemia virus (BLV), which is classified as a Deltaretrovirus, is the aetiologic agent of enzootic bovine leukosis (EBL), a chronic lymphoproliferative disorder with a worldwide distribution. EBL is widespread in dairy herds and causes a direct economic impact due to reduced milk production and the early culling of BLV-infected cattle. The BLV infection status in Taiwan remains largely unknown; a high prevalence of BLV in dairy cows was recently revealed. The present study further investigated BLV infections in beef cattle. Surprisingly, the prevalence of BLV proviral DNA was as low as 11.8% (23/195), which is significantly lower than that noted in dairy cows, which was 42.5% (102/240) (p < 0.001). Factors associated with BLV infections were subsequently investigated. Due to the differences in herd management, an analysis of risk factors for a BLV infection was independently conducted in these two sectors. Several factors associated with a BLV infection were identified. Age was significantly associated with BLV infection status in dairy cows (p < 0.001) but not in beef cattle. A high prevalence of BLV was observed in cattle >15.5 months old (57.8%) compared with those ≤15.5 months old (11.4%). Moreover, after stratification analysis, based on the critical age of 15.5 months, as determined by the receiver operating characteristic (ROC) curve, a significantly higher BLV prevalence was demonstrated in lactating dairy cows, cattle undergoing bull breeding, heifers at older ages, and those undergoing routine rectal palpation. Due to the high prevalence of BLV in Taiwan, the development of an effective control program, based on the identified risk factors, is important for interrupting the routes of BLV transmission within herds.
Highlights
Bovine leukaemia virus (BLV), belonging to the Deltaretrovirus genus of the Retroviridae family, is the causative agent of enzootic bovine leukosis and is the most common neoplastic disease of cattle
Given that BLV prevalence in beef cattle in Taiwan remains unknown, the BLV infection status in beef cattle was initially investigated by nested polymerase chain reaction (PCR)
Considering that herd management and medical practices can vary among countries, this study determined the prevalence of BLV proviral DNA in beef cattle and evaluated the risk factors associated with BLV infection between beef and dairy cows in Taiwan for the first time
Summary
Bovine leukaemia virus (BLV), belonging to the Deltaretrovirus genus of the Retroviridae family, is the causative agent of enzootic bovine leukosis and is the most common neoplastic disease of cattle. BLV infection is mostly asymptomatic, but in less than 5% of infected cattle, it manifests as a malignant B-cell lymphoma [1]. A negative association has been reported between herd-level milk production and herd BLV prevalence in Canadian dairy herds [2,3]. BLV infection has a negative impact on cow longevity [4,5] and restricts the international trade of infected animals. Whether BLV may play a direct role in human diseases requires further investigation
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