Why it's time to control bovine leukemia virus.

Many of us were taught in school that a small percentage of US cattle had bovine leukemia virus (BLV), and its impact was so small that control was not necessary. A lot has changed. Bovine leukemia virus has spread and now infects almost half of US dairy cattle and about a third of our beef cattle. We have learned that BLV disrupts immune function and can indirectly reduce milk production and shorten cow lifespan. Recent claims of human health risks need to be evaluated, and animal welfare aspects must be addressed. These issues will become more important as the dairy industry competes with nondairy alternatives. Fortunately, 2 new BLV control methods are made possible by a new diagnostic test that measures each cow's shedding of infectious particles. Control is possible by culling the usually small minority of cows that are responsible for most of the transmission. The genetic linkage to high BLV shedding has been found to be remarkably strong, and it is anticipated that animal breeders will soon start offering sires with alleles associated with low-level BLV shedding.