The implication of BLV infection in the productivity, reproductive capacity and survival rate of a dairy cow.

The objective of the present study was to find out whether BLV infection, known to cause immunodisturbances in cows, might also bring about decreased productivity, reproductive rate and a shorter life span. More than 100 pairs of dairy cows, and a whole population of 3000 milch cows, were studied for this report. The findings revealed that a BLV-positive cow had a shorter life span than both its seronegative counterpart and the entire milch cow population. It also produced a total of 3.5% less milk and had a mean of 48 more days open than did the BLV-negative cow. The differences in survival rate were highly significant, while, at a level of 5%, those of productivity and reproductive rate were not. The implications of these findings are discussed. A highly significant correlation was also shown between BLV infection and the persistence of Trichophyton verrucosum infection in cows. The presented data indicate that BLV infection might affect the immune system of a cow to such a degree that it ceases to be productive enough to be kept within a herd. Thus it is usually culled before any severe symptoms of disease emerge.