By Ash Keown, Te Awamutu
At this time of year veterinary inboxes all over the district are filling up with ‘BVD emails’. Most dairy herds are signed up to the LIC bulk milk BVD screening scheme, which takes 3 milk samples from the vat at different times over the season. These bulk milk samples are tested with 2 different screening tests:
2 samples are tested for actual BVD virus (current infection)
3 samples are tested for antibody levels (previous infection)
These test results give your veterinarian a good picture of how BVD is affecting your herd. Dry stock farms aren’t quite as easy to monitor – but a quick blood test is all that’s needed.
Bovine Viral Diarrhoea (BVD) is a virus affecting cattle (mostly…). It’s got a terrible name, because diarrhoea is very uncommon with this disease! Cattle can become infected at any time (young or old) by contact with other infected animals. Most animals will show NO sign of infection.
The two major effects of BVD infection are:
Immune suppression – infected animals are more likely to get other diseases such as pneumonia, diarrhoea, and mastitis. It also causes slowed growth of calves and reduced milk production in milking cows.
Poor reproductive performance – this looks different depending on WHEN the cow gets infected:
Infection at the time of mating causes loss of the early embryo (poor conception rate, more returns to service, lower 6-week in calf rate, greater calving spread).
Infection during the 1st trimester creates Persistently Infected (PI) calves, or causes abortion (slips).
Infection during the 2nd trimester causes abortion, abnormal calf development (deformed calves), and stillbirths.
Infection during the 3rd trimester appears to have no negative effect on the calf.
While all the effects of BVD are negative, the worst of all is the creation of PI calves (formed when the mother is infected with BVD in the 1st trimester). At this time, the calf’s immune system isn’t activated and will ‘accept’ the BVD virus as being part of the calf. As a result these calves are infected with virus for their whole life, and are a massive source of infection to all other animals. Many PI calves do not show any sign of disease, so do not assume they are easy to pick out!
Most veterinarians discuss BVD with their farmers every year, but it’s still estimated $150 million is lost from the industry as a result of BVD infection.
In mid-2017 a Sustainable Farming Fund project called ‘BVD-Free’ was launched to investigate the true impact of BVD on the New Zealand cattle industry and see whether a national eradication programme is feasible.
Farmers are being invited to participate in this project – and registrations are wanted now! Check out www.bvdfree.org.nz to learn more about BVD and to get involved in the future of BVD control in New Zealand!