Bovine viral diarrhoea (BVD) can quietly reduce herd fertility, productivity, and profitability long before obvious clinical signs appear. Regular monitoring, strategic vaccination, robust biosecurity, and early identification of persistently infected (PI) animals are key to preventing losses and protecting herd performance.
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/or 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 they reach a steady state of production and fertility that will be reliably lower than optimal levels.
Monitoring – Dairy farms
It is recommended that all dairy farms carry out BVD milk monitoring. It is not a huge expense in the calendar year and provides valuable information for minimal intervention. You can organise this through your veterinarian. 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, thus 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 straightforward when compared to dairy. BVD exposure is monitored in beef herds with blood testing. Emphasis is put on testing the right animals and enough of them. Discussion with your veterinarian prior to testing is critical. What happens out on the hill is an important consideration for many beef breeding units.
Monitoring – Calves
Some farmers opt to blood test or ear test all replacement calves to screen for BVD in order 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 lives.
Bulls
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 because, 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 as to what their BVD policy is.
Vaccination
BVD vaccination is very effective in controlling BVD, by reducing the risk of PI formation. Vaccination is not expensive compared to a herd breakdown in BVD security. Often in extensive beef breeding units, it is the best form of security. Please chat to your veterinarian if you would like to start a BVD vaccination programme.
Biosecurity measures:
Unfortunately, many herds that consider themselves “closed “are in fact not as closed as they think, so it is important to consider all interactions your herd may have.
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 veterinarian to discuss BVD and your farm.
This article was originally published by Totally Vets. As a trusted partner of Vetlife, we’re proud to share their expertise with our community.
