Advice on BVD vaccination for autumn block-calvers

As autumn block-calving builds momentum, herd managers need to check they have remembered to slot in their annual boosters against bovine viral diarrhoea at least one month before mating starts.

Whether they are front-end loaders or tail-end stragglers, all cows and calving heifers in the block can be injected on the same day to maintain herd protection.

National eradication programmes have resulted in fewer dairy farms seeing full clinical signs of bovine viral diarrhoea (BVD).

See also: Advice on how to maintain a tight calving block

But Cheshire-based vet Laura Donovan, from Nantwich Farm Vets, warns that there are always biosecurity risks: very few herds can keep BVD out, she says.

That is why vaccinating and maintaining immunity are an essential part of a control programme.

The issue for block-calving herds, however, is that all cows are at the same stage of pregnancy at the same time.

This creates a greater risk of more persistently infected (PI) calves being born when more cows are exposed to the virus.

Effect on herd health

Laura explains that a PI calf is created when a cow is infected during the first 120 days of gestation because the foetus has not fully developed its own immune system.

“Vaccinating before serving prevents a calf being born as PI. Very big outbreaks of BVD in a block herd would be an explosive catastrophe,” she says.

While there are no research data to confirm how many calves born to infected cows would be PIs – it could be one, it could be all of them in a batch – even one PI heifer would have a big effect on herd health, shedding virus for the rest of its life.

And in a herd where all heifer replacements are born in a tight timeframe, BVD infection could create a large proportion of PI calves.

The result would significantly affect replacement rates, culling numbers and costs.

“Calves living with a PI animal are more poorly than normal if they contract scours or pneumonia because BVD affects their immune system response.

As PI calves release virus, they spread acute infection to others in the group.

A PI calf can look normal, or might not grow properly and, if they get to 12 months, they can go downhill and become very poorly as the virus mutates into mucosal disease,” Laura says.

Vaccine choice and timing

Block-calving herds have the advantage in being able to plan BVD vaccinations as one annual event, making it simple to keep track of herd status and timely boosters.

With two vaccines on the market, each with different protocols, Laura suggests discussing with your vet which products can be combined with protection for other diseases such as leptospirosis or infectious bovine rhinotracheitis.

Vaccine choice also dictates the protocol and timing for future annual boosters.

As most block-calving herds like to front-end load with heifers, it is important to factor this into the timing of injections and product use.

Laura points out that the dead BVD vaccine requires a course of two doses, four weeks apart, followed by another dose six months later, before a programme of annual protection.

The primary dose in heifers has to be before first service.

With boosters, timing is less critical, as long as it is as close to the 12-month interval as possible, she says.

“Autumn-calving herds can do heifer checks in July or August [testing unvaccinated heifers for BVD antibodies to establish the herd’s current BVD status and identify if there has been exposure to infection] before vaccinating them in September, ready to serve in November.

“Also, vaccinating can fit in with another husbandry procedure. We often do it on day two of a TB test and at the same time as worming or fly control.

“This reduces the stress levels of handling and cows can be done as they exit the parlour.”

Vaccination for bulls

Stock bulls need to be isolated for at least three weeks after arriving on farm and vaccinated for their own protection, whether hired, borrowed or bought.

“When bulls are infected by BVD, they have a high temperature, which affects semen quality for as long as two months after infection. The virus can also be spread in semen, causing early abortions or PI calves in the herd.

“A PI bull is a reservoir of infection and will continue to shed virus. It’s important to test them before purchase and on arrival because a PI bull will affect your herd’s fertility and this, in turn, will affect your block.”

Cost to herd

According to BVD England, having BVD circulating in your herd can cost up to £552 a cow a year.

Laura agrees it can be hard to calculate the exact cost for a herd, but says it is cheaper to follow a plan of regular testing and vaccination.

She also reminds block-calving herds to consider the losses associated with an extended calving period, rising empty rates, more culls and the cost of rearing replacements.