15 Aug 2023
Tonia Simms
Job Title
The author discussing key health issues with a farmer.
Latest developments in Government incentives and farm assurance schemes should encourage more farmers to test cattle to stamp out bovine viral diarrhoea (BVD), but English herds might still be left behind.
As of October 2022, Red Tractor stipulated that beef farmers must have a BVD eradication programme in place to receive farm assurance accreditation, bringing beef standards in line with dairy.
The move is a positive one and alongside England’s APHA Animal Health and Welfare Pathway (AHWP) funding BVD blood samples, this should encourage more farmers to test for BVD. But more must be done to motivate all dairy and beef herds to adopt BVD control strategies and prevent trade disparities across UK nations.
BVD is endemic in the UK and causes abortion, infertility and production losses through immune system depression. UK strategies to control it have been left in the hands of devolved nations, with each one adopting a different approach: Northern Ireland and Scotland have forged ahead with compulsory schemes, leaving Wales and England lagging behind. This has already caused trade disparities across the UK – particularly for pedigree stock, with 90% of herds in Scotland now BVD free as well as TB free.
In Wales, a consultation to make BVD testing compulsory has now closed and we are awaiting the outcome. If BVD testing is made mandatory, it would be a welcome move for Welsh disease control, but one that could leave English cattle farmers out in the cold.
The risk is that it will make English stock less favourable in other devolved countries – particularly along the borders – in livestock markets such as Shrewsbury and Welshpool, where both English and Welsh cattle are traded, or Carlisle and Sterling for England-Scotland trade.
Persistently infected (PI) animals occur when a cow is infected in the first approximately 120 days of gestation.
Her calf becomes infected before its immune system develops and the calf assumes the virus as part of its DNA. The calf is born PI, which means it can spread the virus to other animals throughout its life.
Transient infection occurs when naive healthy animals are infected. They subsequently fight off the disease, but it can still cause big production losses, resulting in diarrhoea for up to two weeks and significant drops in milk yield.
In youngstock, often we will see a group of calves succumb to respiratory disease – even if they are vaccinated – because the vaccine will not work if the immune system is suppressed.
Therefore, more must be done to encourage English herds to test.
Vets have a real opportunity to encourage this through the AHWP. Launched as part of the Sustainable Farming Incentive, the programme will fund an annual visit from a vet, of £372 for dairy cattle and £522 for beef animals. As part of this, farmers will be required to screen for BVD.
The AHWP represents a good opportunity for farmers who do not see the vet regularly – particularly beef farmers. It will give vets the chance to discuss underlying herd health issues and make herds more efficient and healthier for the future.
Talk is increasing in the industry around sustainability and how farmers can become more efficient, but as vets, BVD control is an easy win.
Many farm businesses are trying to make efficiencies in the face of rising production costs and BVD is counterproductive to this.
BVD costs the industry about £70 million annually, but unfortunately, unless an abortion storm or a respiratory disease outbreak is happening, it is often a hidden cost that farmers cannot see. Therefore, it can be difficult to persuade clients to test.
Youngstock infected with BVD will have lower daily liveweight gains and take longer to finish. Meanwhile, infected adult cows will produce less milk and have poorer reproductive performance. Reduced performance and food conversion efficiency increases methane production per productive unit, but also increases antibiotic use requirements, too.
A lot of herds remain unaware they might have BVD, and simply accept higher-than-average morbidity and mortality, but it is our responsibility as vets to take a step back and look at the whole herd performance to see if BVD is the underlying cause of poorer performance.
Vaccination is a key part of control. Many of the older BVD vaccines require two primary doses, given four weeks apart, followed by a booster every 6 to 12 months. But in some herds, despite what the vaccine data sheet says, farmers vaccinate annually before breeding, and time may have lapsed in between courses, which begs the question: is BVD control as good as it could be?
The newest BVD vaccine on the UK market is a live vaccine that only needs one injection per year. This has allowed improved compliance with vaccines and better fetal cover.
Some farmers vaccinate all stock, but never search for persistently infected (PI) animals. As a long-term strategy, strict vaccination schedules will get rid of the problem, but if these lapse and those PI animals are sold, they could spread it to other farms, so more focus must be placed on rooting out PI animals.
If farms are naive to BVD infection, they must be overzealous and make sure they do not bring BVD on to their farm, because the effects can be catastrophic both short-term and long-term.
When animals are bought in, they should be isolated for four weeks and tested for BVD after this period. Purchasing pregnant animals is high risk: a cow that tests positive for antibodies could be presumed to be immune, and therefore not going to spread the disease to the rest of the herd.
However, no way exists of testing the calf in utero if she is pregnant, and the risk is that you will introduce a PI calf into a group of pregnant animals – possibly potentiating the spread of disease.
We recently had an outbreak in an accredited herd caused by a bought-in pedigree heifer that gave birth to a PI calf. The immediate effect on neonatal calf health was dramatic, with massively increased losses. Then the long-term effects on cow and bull reproduction carried on for 9 to 12 months after initial infection.
Farmers should only buy from accredited herds and avoid buying through the market. Even if that animal is accredited BVD-free, the risk is that it has been in a pen next to non-accredited herds and may have caught the disease.
To protect the spread of disease from neighbouring herds, boundaries should always be double-fenced, allowing 2m to 3m between the fence to prevent nose-to-nose contact between cattle.
I would encourage all naive herds to vaccinate animals against BVD so they have protection in case of an outbreak. All breeding stock should be vaccinated at least two to four weeks before the bull goes in with the cows, to protect the calf from becoming infected and being born PI.
Various ways are available to test – in a dairy herd, the easiest way is to routinely monitor bulk milk antibodies for BVD. Antibodies are long-lived and can last 8 to 10 years, so knowledge of the history of the herd is necessary in case of previous outbreaks or vaccination.
If the bulk milk sample is positive, further testing would be required – normally a bulk milk antigen PCR (for tanks holding fewer than 300 cows’ milk) or a youngstock blood screen of five animals per management group between 9 and 18 months old.
If this flags up a positive animal, we will then encourage farmers to start tagging and testing their calves from birth. This involves taking a small tissue sample from the calf and testing it for the BVD virus. It is the more expensive screening option as it involves testing all calves. However, it allows you to be in complete control of all animals born and then trace the disease back to older animals. Please note, all abortions and stillborn calves should also be tested to ensure complete BVD surveillance.
BVD antibody tests show the animal has come into contact with BVD, through infection or vaccination, but will not confirm the animal is a PI. For this, animals must be tested for virus antigens.
To reliably detect the presence of antigens, animals testing positive should be isolated and retested two weeks later to eliminate the possibility of transient infection. If the test is positive, it can be assumed the animal is a PI and should be culled.
Government policy is moving in the right direction, and as vets, we must encourage farmers to take advantage of these schemes. The first step towards BVD eradication is understanding herd health status, so plans then can be put in place to rid the herd of disease.
Hopefully, by vets starting these conversations, it will lead to wider discussions around infectious disease, which can help drive real improvements in animal health and efficiencies on farms that contribute to a more sustainable and profitable farming sector.
Tonia Simms
Job Title