Bad biosecurity to blame for BVD persistence
Less than 5% of New Zealand dairy and beef herds are completely closed to contacts with other cattle herds, which is placing them at significant risk of BVD outbreaks and likely keeping the disease at its current high prevalence levels.
Background
Estimates from the field suggest that as many as 5 - 10% of cattle herds in New Zealand could be experiencing new BVD outbreaks each year at an average cost of $22.22 per milking cow per year for dairy herds and $41.19 per mixed-age cow per year for beef herds over a 5-year period. We know that the three main ways for BVD to enter a herd are through purchasing new cattle, sending cattle on and off site for grazing, and allowing cattle to have nose-to-nose contact with stock from neighbouring herds over fenclines.
Knowing how much each of these factors contributes to the risk of BVD outbreaks is important for making more targeted recommendations about preventing BVD spread.
Study Objectives
The objective of this study was to understand how biosecurity practices influence the risk of herds being positive for BVD and what impacts this might on BVD levels in the cattle industry.
Did you know……….
Many of the biosecurity measures that will protect your cattle against BVD will also protect them against other harmful diseases. This includes installing double-fencing in fields where stock have nose-to-nose contact with neighbours, isolated new stock from the main herd for 14 days, and disinfecting any equipment, vehicles, and clothing that have been in contact with cattle from other farms.
Methods
From September 2015 to December 2016, MSD Animal Health sponsored a national ”Take the BVD Test Challenge” project to get updated information about the percentage of herds with active BVD and their risk factors for BVD. The initiative was advertised to all veterinarians across New Zealand who were asked to collect whole blood samples for BVD testing and administer a BVD risk factor survey whilst visiting an eligible farm for other animal health reasons. For each enrolled farm, 15 apparently healthy animals between 1 and 2 years of age were randomly selected from the replacement heifer herd. Serum samples were collected from each animal and shipped to a commercial diagnostic laboratory for a pooled serum antibody ELISA test to check their BVD status. During the sampling visit, farmers were asked to complete a short survey about their herd management, biosecurity practices, and BVD control programmes.
As part of building the business case for BVD eradication in New Zealand, we also developed simulation models of how BVD spreads within and between herds through animal movements and contacts with neighbouring herds over fenceline boundaries to explore the impacts of biosecurity measures on the ability of BVD to stick around in the New Zealand cattle industry.
Results
Out of the 308 participating farms, 57/116 (49.1%) beef farms and 95/188 (50.5%) had antibody levels that were consistent with having active or recent exposure to BVD in the herd. These results were not completely surprising since fewer than 5% of herds self-identified as being completely closed to contacts with other herds. Almost all farms reported purchasing or leasing at least one bull each year and about a third of farms also bought extra female animals as breeding replacements. However, fewer than 50% of these farmers had any kind of biosecurity measures in place to prevent BVD from being introduced through these animals. Farmers who said they had good knowledge of BVD were no more likely to have biosecurity measures in place than farmers with poor awareness of the disease.
The odds of a herd having an active BVD virus infection were about 2.2 times greater in farms with onto-farm movement of heifers/cows (95% CI: 1.29–4.24) compared with farms that had no onto-farm movement of heifers/cows during the last five years, and the odds of having active BVD virus infection were 2.7 times greater in farms with occasional/rare animal contacts between farms (95% CI: 1.33–5.41) compared with farms that never had close between-farm contacts.
When we ran the computer simulation models to look at how BVD spreads through the cattle industry, it was almost impossible to get BVD to persist long-term through the direct movements of cattle alone. This highlights the importance of spread through local contacts with neighbouring herds in keeping BVD at its current high levels in New Zealand.
Clinical Relevance
Poor biosecurity in the beef and dairy industries is likely contributing to the spread of BVD as well as many other important infectious diseases. It was interesting to note that farmer awareness of disease was not associated with practicing better biosecurity. There is a need for more work to better understand what biosecurity measures are the most practical and effective for farmers to implement to better protect their herds.