THE EFFECT OF BOVINE VIRUS DIARRHEA VIRUS-INFECTION ON CONCEPTION RATE

The possible influence of bovine virus diarrhoea virus (BVDV) on conception rate was studied in five dairy herds in which animals persistently infected with BVDV were found. In each herd a risk period was defined as the period (starting January 1986) before the oldest of the persistently infected animals was 6 months old. The post-risk period was defined as the period thereafter (ending December 1988). The prevalence of antibody carriers was assumed to be low at the beginning of the risk period; seroprevalences were moderate to high in the post-risk period in each herd. In all herds, conception rate was higher (four of five individual-herd P < 0.10) in the post-risk period than in the risk period. The increase ranged from 16 to 64% of the conception rate in the risk period. The overall significance of the Mantel-Haenszel chi2 test was P < 0.001. Thus, it was strongly suggested that the BVDV infection circulating during the risk period had caused a temporary decrease of the conception rate in the dairy herds.