Bovine viral diarrhea virus (BVDV) infection: Effect on reproductive performance and milk yield in dairy herds.

The impact of an outbreak of bovine viral diarrhea (BVD) on reproductive performance and milk production was investigated in 28 Spanish dairy herds using an observational study design. Mean calving to conception interval (CCI), mean number of inseminations per conception (AI/P) and mean daily milk yield were recorded from herds affected by outbreaks. Infection was confirmed by evidence of viral transmission to young stock (heifers 9-24 months) and persistently infected animals, after previous BVD-free status. Fifteen herds did not use vaccines (G1) whereas the remaining 13 received modified live BVD virus (BVDV) vaccines (G2). In G1 herds, a significant increase in CCI (13.8 days; 95% CI, 0.4-27.3 days; P = 0.050) was observed during the BVD outbreak compared to the year before the outbreak. In G2 herds, there was a not a significant increase in CCI (3.0 days; 95% CI, -1.2-7.2 days; P = 0.558). Changes in AI/P between periods were not significant in any of the herds. In G1 herds, there was an increase of 0.09 units (P > 0.05) during the outbreak, whereas in G2 herds, AI/P decreased 0.08 units (P > 0.05). Compared to milk production in the year before the BVD outbreak, there was no significant change in G1 herds throughout the study period (P > 0.05), but there were significant increases in G2 herds over the study period (P1-P2, 1.4 kg/day increase, P = 0.019; P1-P3, 2.0 kg/day increase, P = 0.007). These results indicate that BVDV infection affected reproductive performance, which is critical in maintaining dairy herd profitability.