Risk factors associated with high bulk milk antibody levels to common pathogens in UK dairies

Infectious diseases pose a severe economic burden on the UK dairy industry. This study used bulk milk antibody levels in 1088 UK dairy herds to estimate the current UK prevalence of bovine viral diarrhoea virus (BVDV), bovine herpes virus 1 (BHV-1) and Leptospira hardjo. Questionnaires collected under the DairyCheck scheme (MSD Animal Health) were used concurrently to gather information on farm demographics and management practices. The prevalence of active BVDV infection was 58.6 per cent, of historic BVDV exposure was 88.6 per cent, of BHV-1 infection was 69.2 per cent and of L hardjo was 71.9 per cent. An increasing herd size and the purchasing of replacement cattle were risk factors for the presence of all three agents. Year-round calving was associated with a 1.9 times increased risk for having BVDV (P<0.005). The presence of a bull was associated with a 1.5 times increased risk for having BHV-1 (P<0.005). When compared with previous results, this study indicates a slight fall in the prevalence of BVDV within the UK dairy herd; however, BHV-1 and L hardjo levels appear to have remained constant. This study shows that herds purchasing cattle are at greater risk of infectious agents being present and therefore, if possible, a closed herd system should be implemented.