Bovine leukemia virus in the U.S. dairy industry

Prevalence and associations with economically important production indicators

Abstract

Bovine leukemia virus is a deltaretrovirus of cattle and the causitive agent of enzootic bovine leukosis. A small proportion of infected animals develop the clinical manifestation of lymphoma, however the majority remain subclinically infected. Infection is common in the U.S. dairy cattle population and in other major dairy producing countries that have not taken steps to reduce and erradicate infection in their populations. The 1997 and 2008 NAHMS dairy studies examined the prevalence of BLV infection at the cow and herd levels, respectively. There has been no updated estimates of prevalence in the U.S. cattle population in the last decade. Within that time, evidence of the negative impact of subclinical infection has been mounting. Cows exhibit alterations in immune function, decreased longevity, and reduced milk production. The first major objective of this study was to provide an updated estimate of BLV prevalence in a multistate sample of U.S. dairy cattle. The second major objective was to measure herd and cow level associations between BLV prevalence and economically important dairy production outcomes, namely milk production, reproductive efficiency, and somatic cell count.