Bovine viral diarrhoea (BVD)

BVD is widespread in New Zealand cattle. Around 80% of dairy and beef herds have evidence of exposure, and current information shows that approximately 4% of dairy herds undergoing routine testing experience a BVD outbreak in the milking herd each year.

BVD can cause reproductive losses, weak calves, reduced growth rates, lowered milk production and increased susceptibility to other diseases. In many herds, the signs are subtle and may show up as poorer-than-expected reproductive or production results rather than obvious illness.

Estimates put the annual losses for dairy farmers at around $127 million, with losses of $70,000 annually for each average sized infected herd ($110-180 per cow).

How BVD spreads

BVD spreads mainly through close contact with infected cattle. The highest-risk animals are PI cattle, because they shed large amounts of virus throughout their lives. BVD can also be introduced through purchased, leased, borrowed or returning stock, including bulls, replacement heifers and carry-over cows.

Off-farm grazing can be a key risk for dairy herds, especially where heifers are grazed with cattle from other farms or return in-calf. Boundary contact with neighbouring cattle can also spread BVD if stock can touch noses across fences.

Persistently infected animals (PI)

The disease is maintained in the herd and spread to other herds by persistently infected (PI) animals.

A PI calf is usually created when a susceptible cow or heifer is infected with BVD during early pregnancy. The dam may show no obvious signs of illness, but the developing calf can become infected before its immune system can recognise and clear the virus.

PI animals remain infected for life. They may look normal, but they continuously shed BVD virus and are the main reservoir for spread within and between herds. Some PI animals become poor doers or develop mucosal disease, which is usually fatal.

Pregnant animals need particular care. A cow or heifer may test virus-negative herself but still be carrying a PI calf if she was infected earlier in pregnancy.

Persistently Infected Carriers Infographic July 2025 V3

Controlling bovine viral diarrhoea (BVD)

BVD control is practical, achievable and cost-effective when it is built into routine herd health management. The aim is to remove existing PI animals, protect pregnant animals from infection, and stop BVD being brought back onto the farm.

A number of things can be done to control BVD: testing animals, monitoring the BVD status of the herd, managing the health status of animals coming onto the farm, and vaccination. Even small improvements can reduce risk, but the best results come from having a clear whole-herd plan.

1. Define if BVD is in the herd

Use testing to understand whether BVD is circulating in your herd. Bulk milk testing is a useful screening tool for dairy herds. Antibody testing can show exposure trends, while PCR or antigen testing can help detect virus in the milking herd.

If test results suggest active infection or recent exposure, work with your veterinarian on identifying the source and a plan to stop further spread.

2. Find and remove PI animals

PI animals must be identified and removed from the herd. They should not be sold as breeding animals or moved in a way that creates risk for other herds.

Test replacement calves early so PI calves are found before they enter the breeding herd. Animals that test positive for virus may be transiently (temporarily) infected or persistently infected, so isolate them and follow veterinary advice on confirmation and management.

3. Assess the level of risk of BVD coming onto the farm

Identify the main ways BVD could enter or spread on your farm, including cattle movements, off-farm grazing, neighbouring cattle, and people, equipment or vehicles coming onto the property.

Focus on higher-risk animals such as purchased, leased, borrowed or returning cattle, including bulls, replacement heifers and carry-over cows. Pregnant animals need extra consideration, as they may be carrying a PI calf even if they test negative themselves.

Review arrangements for heifers and carry-over cows grazing off-farm, especially where they mix with other cattle or return in-calf. Check boundary fences to reduce nose-to-nose contact with neighbouring cattle.

4. Action a control plan to mitigate these risks

Based on your test results and risk assessment, put a control plan in place with your veterinarian. This may include:

Testing incoming or returning animals for BVD virus before they mix with the herd. This includes bulls, purchased or leased cattle, returning heifers or carry-over cows, and calves born from introduced or returning pregnant animals.
Checking the BVD status of bulls before mating. Bulls with previous “BVD clear” results may still need testing if there is a risk they have been recently exposed and could be transiently infected. Keep them separate from the herd until their status is confirmed.
Testing vaccinated animals if their PI status has not previously been confirmed. Vaccination helps protect animals from infection, but it achieves nothing in animals born as PI.
Vaccinating cows and heifers before mating to help protect them during pregnancy, and vaccinating bulls used for mating.
Changing management practices to reduce exposure, such as using quarantine periods, improving boundary fences, and reducing nose-to-nose contact with neighbouring cattle.

5. Monitor to make sure it is working

Regular monitoring will ensure your plan is working. Routine bulk tank milk testing is a practical way to track herd status and pick up changes early.

Ask your veterinarian to work through this process with you – they have tools to assist.