Controlling Johne’s and BVD on farm

Assessing stock for signs of Johne’s disease and BVD eradication were topics up for discussion at the recent, SAC BVD and Johne’s disease awareness campaign at Corbieton, Haugh of Urr, Castle Douglas, Aly Balsom reports

Farmers should critically assess this year’s calf crop, as uneven batches could be an indicator of underlying disease problems, said Colin Mason, SAC vet investigation officer.

“Weaning is an ideal time to assess calf performance. Pass a critical eye over batch-born calves and look for uneven groups – poor doers could be a sign of underlying Johne’s disease in the herd.

“One of consequences of Johne’s disease is a reduction in milk yields – this will manifest itself in low calf growth rates, poor calf viability and a higher level of neonatal disease in suckler herds,” Mr Mason explained.

Johne’s disease can also result in increased weight loss in adult animals. “In suckler herds, our main aim is to manage body condition so any disease challenge that affects condition is undesirable.

“The key is to identify problem cows when they are still worth money. Culls with a good body condition are potentially worth £1000 compared to £200 for low condition cows, or a £120 cost for casualty animals.” Consequently, the cost of a testing scheme at about £700 is a cost easily recovered.

Johne’s control should include a test-and-cull strategy, continued surveillance and assessment of risks associated with breeding and replacement policy, he said.

“Herd status should constantly be re-assessed – nothing stays the same forever.”

Assessing cull rates and reasons for culls can also be a good indicator of a Johne’s problem. “If there is ever likely to be an area where Johne’s is present, it will be in your cull animals, so these are a good group to test.”

However, Johne’s disease is not as easily controlled as BVD. “Due to the complexities of infection, Johne’s is one of the major diseases facing suckler producers.”

Johne’s disease can be present in the herd in a complex pyramid of infection, Mr Mason explained.

“On top are the obvious, clinical cases, but under the surface are a group of cows showing no obvious signs of disease. These may show some sub-clinical signs and may test positive after bloods are taken.”

Below this group are a batch of animals that test negative, but as time goes by, these will move up the pyramid and become positive. “How wide this base of the pyramid is, will depend on individual farm purchase practices.”

“Remember, for every one clinical case, there will be numerous other infected animals within the herd.

“A lot of people think of Johne’s spread within the cow/calf unit, but in fact the disease can spread from animal to animal, with calves in their first year of life being most susceptible,” he said.

The disease can be spread in milk and faeces and in some situations, directly to the foetus.

“Spreading dung on grazing fields could potentially create a risk of disease spread, so farmers should carefully consider where they put young stock.” But slurry injection may reduce the risk of Johnes spread by limiting the amount of leaf contamination.

Case study:  Donald Biggar, Corbieton, Castle Douglas

Since re establishing his 320 cow suckler herd of beef Shorthorn and Aberdeen Angus after foot and mouth, Donald Biggar has put a firm emphasis on disease control in both his pedigree and commercial herds. All cattle are in the SAC Premium Cattle Health Scheme.

Johne’s control

“I can remember the sinking feeling in my gut when Johne’s was identified,” said Mr Biggar.

“A cow can quickly turn from an asset to a liability – the key is to get rid of her before she becomes clinical and is still worth something,”

Everything more than two years old is now tested every year and all positive, suspicious or inconclusive animals are culled.

However, sometimes it is not as clear cut as simply testing and culling animals, he said. “When a cow tests positive at nine years old and she had a good quality calf born when she was two years old, we may chose to monitor her progeny closely by testing every six months, rather than cull.”

Since addressing Johne’s control, there has also been a marked improvement in fertility rates, said Colin Mason, SAC vet investigation officer.

“Barren rates have improved from 8% in 2008 to 3.5% this year. Calf losses have also reduced to 3.3%, but we are targeting 2%”

Since tackling disease, we have definitely seen the benefits in terms of improved herd health and performance, Mr Biggar agreed.

The pedigree herd has now been clear for two years.

BVD control

After a disease breach within the pedigree herd when stock mixed with a neighbour’s animals, the farm adopted a test and control programme for BVD.

“Tests revealed some heifers were antibody positive, suggesting they had been exposed to a persistently infected animal (PI),” said Mr Biggar.

“The following spring, we tested for virus in the calves and culled any virus-positive animals.”

Since then, six to eight calves from each management group, at nine months of age are tested for BVD antibodies every year. Breeding heifers are vaccinated prior to mating and all breeding females are vaccinated annually thereafter.

“Our pedigree herd is now accredited BVD free and the commercial herd is continually monitored.”

cow with calfBVD-free stock

All producers selling breeding stock should be in a health scheme, said George Caldow, SAC regional vet manager.

“The basic requirement for selling stock is buying and selling BVD-free animals and there is absolutely no barrier to achieving this.

“Recent sales at Aberdeen Northern Mart, where producers received a premium for BVD free stock, has proved selling disease free animals is worthwhile.”

And farmers can get the benefits associated with selling disease-free stock by using a testing and screening programme.

“It will take 12-24 months before farmers can be accredited disease free, but in the meantime, by being part of a health scheme and receiving a NFUs/QMS certificate signed by the vet and farmer, farmers can receive the market return in trading disease-free animals.”

And this does not have to be limited to Scottish farmers, said Mr Caldow. “There is nothing stopping farmers in the rest of the UK from using this certificate for trading stock.”

However, when looking at the continued cost of testing, vaccinating and certification, going for full Cattle Health Certification Standards BVD free accreditation is a cheaper way of achieving BVD-free status in the long term, he said.

“And if it is cheaper to do this, then it is also cheaper to eradicate BVD on a national level.”

If we can eradicate TB in Scotland, then why not BVD? he asked. “My aim for Scotland would be to eradicate BVD completely – and we are currently taking the right steps to achieve this.

Awareness and momentum is growing in terms of disease control, said Mr Biggar. “If we are awarded TB-free status and move from four year to six yearly testing, this will free up a lot of money that could be used to implement a BVD eradication programme in Scotland.

“The potential rewards of such a scheme could be enormous.”