Investigation of bovine leukemia virus seroprevalence and transmission risk classification based on blood proviral load in beef breeding cattle in Ibaraki Prefecture, Japan.

This study investigated the seroprevalence of bovine leukemia virus (BLV) in beef breeding cattle in Ibaraki, revealing a seroprevalence of 43.0% with a bimodal distribution in farms classified as either BLV-negative or very-highly infected. These results underscore the need to implement appropriate strategies for very-highly infected farms. In particular, determining the culling prioritization of cattle is absolutely necessary. It was revealed that effective control in very-highly infected farms is difficult based on types of operation or herd size. On the other hand, high-transmission-risk cattle were widely distributed across entire Ibaraki and were significantly more prevalent in very-highly infected farms. These findings suggest that the transmission risk classification is a potentially effective strategy for culling prioritization under the current circumstances in Ibaraki.