BVD could be "baaa-d" news for sheep and beef farmers

Author: Caitlin Evans

Lambing ewes and beef cattle grazed in neighbouring paddocks

Traditionally bovine viral diarrhoea (BVD) has been considered a disease of cattle. Recently however, it has been reported to cause infections in many other species including sheep, deer, alpacas, llamas and pigs. Recent work in Australia has shown that sheep are not only susceptible to infections with BVD but that transient infections in pregnant ewes can result in severe lambing losses. Lambing rates as low as 32% were reported in infected flocks, while lambs born weak, with physical abnormalities or persistently infected (PI) with BVD were also observed. Unlike in cattle, the survival of lambs infected with BVD, both transiently and persistently, were poor. A study of antibodies to BVD in South Australian sheep flocks was also studied with results indicating that in the flocks tested, BVD was not common. How well this translates to New Zealand remains unknown.

As such we must be cautious about the role sheep play in the spread and persistence of BVD in New Zealand. This is of particularly concern in regions where sheep and cattle are co-grazed or housed in close proximity to one another. In 2017 New Zealand farmed 27.37 million sheep and 10.08 million cattle (both dairy and beef). Add to this the fact that beef and sheep farming was the most extensive agricultural activity in 2016 and the potential for BVD to persist in both sheep and cattle herds is high.

While the work from Australia indicated that the survival of PI sheep is poor, this does not mean that sheep flocks do not pose a risk to the spread and persistence of BVD in New Zealand. The presence of any PI animal on farm, no matter for how short a period of time, poses a risk to the health and productivity of the rest of the animals on that property. As such, we must be aware that in instances where sheep flocks are presenting with abnormally low lambing rates, or high instances of lambs born with developmental abnormalities then BVD should be considered as a potential cause. Similarly, contact between cattle and sheep around the time of mating and pregnancy should be avoided where possible.