BVD is a common but complicated disease. The production and reproductive costs of the disease are insidious and difficult to calculate. Eradicating BVD often comes with significant productive and reproductive improvements.
Hopefully most farmers have some familiarity with the disease process by now. Transmission occurs faeco-orally and nose to nose over the fence. Usually transmission is from Persistently Infected (PI) animals to naïve cattle (animals with no previous BVD exposure). PI cattle shed high levels of the virus in their body fluids for their entire lives. PI calf creation occurs when naïve cows are exposed to BVD when they are 40-150 days pregnant.
Introduction of BVD into a naive herd at critical times in the breeding season can cause mass abortion and creation of new PI calves. Herds that are living with PI animals usually show moderate to high levels of immunity to BVD and reach a steady state of production and fertility that will be reliably lower than optimal levels.
Monitoring – Dairy farms
I would recommend all dairy farms carry out BVD milk monitoring. It isn’t a huge expense in the calendar year and provides valuable information for minimal intervention. You can organise this through your vet. The test is run on a bulk milk sample which can usually be sent to the lab directly from the supplier with minimal effort to the farmer. The sample is tested for BVD exposure (antibodies) and PI animal presence (antigen). The bulk milk is tested for BVD antibody 1-3 times a year, monitoring for BVD exposure throughout the season. The antigen test is usually only performed once or twice at the start of the season. Ideally the antigen test should be done on a day when all heifers have calved and are contributing to the vat. This then screens all heifers for PIs allowing you to catch them before mating starts.
Monitoring – Beef farms
This is not as straight forward when compared to dairy. BVD exposure is monitored in beef herds with blood testing. Emphasis is made on testing the right animals and enough of them. Discussion with your vet prior to testing is critical.
Monitoring – calves
Some farmers opt to blood test or ear test all replacement calves to screen for BVD to save on costs of rearing a PI animal. This type of screening also removes the risk of PI calves causing abortions and PI creation in their peer group when they reach sexual maturity and with other cows on the farm that they may come across in their life.
Any bull that comes onto your farm should be BVD tested and vaccinated. If the bull is a PI, he will wreak havoc on the repro results that year and run the risk of PI creation in that crop of calves. Vaccination is necessary as if the bull contracts BVD leading up to the mating period or during mating his semen production will suffer. Please check with your bull supplier what their BVD policy is.
BVD vaccination is very effective in controlling BVD, by reducing the risk of PI formation. Please chat to your vet if you would like to start a BVD vaccination program.
BVD can be very complicated to understand and insidious in how it shows up on your farm. Each farm requires an individual approach to monitoring, prevention and control. As it goes with BVD, intervention always carries a cost benefit when compared to doing nothing. Please chat to your vet to discuss BVD and your farm.