Analysis of individual farm investigations into bovine viral diarrhoea in beef herds in the North Island of New Zealand

AIMS: To use data from individual farm investigations of herd bovine viral diarrhoea (BVD) status and risk factors to estimate the prevalence of recent active BVD virus (BVDV) infection in beef herds in the Waikato, King Country, Wairoa and Gisborne areas of New Zealand; to identify farm management factors associated with BVDV infection in these herds; and to gain a better understanding of farmers' attitudes to BVD.METHODS: Data from 43 farm investigations were combined. Each investigation involved collecting blood samples from 10 to 15 rising 2-year-old replacement heifers (n=637) to test for individual antibodies to BVDV using ELISA. A farm was classified as having evidence of recent active infection when more than 20% of samples were positive. At the time of sampling a risk assessment questionnaire was completed to collect information about farm management practices and farmer attitudes. The influence of these factors on the odds of there being evidence of recent BVDV infections on the farm was then analysed using logistic regression modelling.RESULTS: Of the 43 herds, 25 (58 (95% CI=43-71)%) had evidence of recent active BVDV infection. The percentage of such herds did not differ between the four areas (min 55, max 67%; p=0.87). Four factors were identified as contributing to the odds of a herd being classified as having recent active BVDV infection. Increasing numbers of heifers on the farm, introducing replacement heifers, and the farmer considering BVD was an issue on the farm were all significantly associated with increased odds of active infection; whereas vaccinating introduced breeding bulls was associated with decreased odds of infection.CONCLUSIONS: The results are consistent with earlier studies that found BVD was widespread in beef herds throughout New Zealand. Farm management factors that may influence the odds of active BVDV infection have been identified.CLINICAL RELEVANCE: Pooling data from individual herd investigations of BVD status can significantly add to the value of those investigations and provide information that can identify potential risk factors for a practice area. With these local data now available, our clients should have greater confidence in the need to proactively manage BVD on their farms.