Fature: Kelvin Green

Tackling BVD in your suckler herd can improve fertility and boost calf numbers as proved on one Hampshire suckler farm

With Persistently Infected animals responsible for 85% of BVD transmission, culling these animals and protecting breeding stock through vaccination is essential to control disease spread, according to vet Keith Cutler, Endell Vet Group.

“Persistently infected animals (PIs) are the main source of BVD infection, with just 15% of transmission spread from acute infection,” he explains.

A PI is formed when a cow becomes infected within the first third of pregnancy. Her calf will always be infected and shed the disease. Equally a PI cow will always produce a PI calf. “The only way to deal with a PI is to cull them out of the herd and reduce the rate of transmission.”

And this strategy has been adopted by Hampshire-based Kelvin Green who farms 150 spring and 60 autumn block calvers at Cowlease Farm, Romsey.

Kelvin Green of Cowlease Farm, Romsey, knows how to tackle BVD in his suckler herd

The herd has a dairy cross base which is crossed to Aberdeen-Angus and Simmental bulls. The farm also has a small herd of pedigree Aberdeen-Angus which they use to breed their own bulls.

“After identifying a PI in the bulling heifers about four years ago we started vaccinating the whole herd as part of an ongoing drive to improve herd health,” explains Mr Green.

“We used to buy in replacements, but after a TB scare with bought in stock, we decided something had to be done.” Since then, the farm has moved towards managing a closed herd and controlling BVD and Leptospirosis.

Initially a small, sickly heifer was singled out for poor performance and blood tests identified her as a PI, explains Mr Cutler. “PIs are not always obvious, but can show themselves as runty animals that may fail to respond to treatment.

“Once a PI has been identified, they must be culled immediately. You then know BVD is present in the herd so the next step is to prevent more PIs from being born and vaccinate.

“The key is to prevent heifers from becoming infected and protect the unborn calf. The strategy undertaken at Cowlease Farm is a good example of correct testing and vaccination policy. When heifers are selected as replacements they are then tested to see whether they are a PI.”

After tests come back negative and before first service, these heifers are vaccinated for the first time. “It is vital vaccination is carried out before service. Animals need to be protected before pregnancy and specifically in this first third of pregnancy.”

But the way you tackle disease will be farm specific, he stresses. “The quickest way to control BVD is to test all cattle at once and cull all PIs, but this is extremely costly.”

The second option, and the one implemented by Mr Green is to accept BVD is in the herd, but test replacement animals and vaccinate all breeding stock to prevent PIs from being born. And when a homebred heifer is identified as being a PI, the next step is to find and test her dam.

“Over a period of time the whole herd will have been tested, but the cost will be spread out.” And in a few years Cowlease Farm will be BVD free.

Having implemented these changes, fertility has shown marked improvements, says Mr Green. “Our calving pattern is much tighter with the majority now calving in a six week block. Out of our 150 spring calvers, we only had four that were PD negative.

“When buying in bulls, farmers should seek re assurance of the herd’s status and preferably only purchase stock from BVD accredited free herds.” Any bought in bulls at Mr Green’s are blood tested for virus and antibodies as an extra security measure.

A practical guide to BVD management and control

BVD, Bovine Viral Diarrhoea, is a viral disease with a wide range of clinical signs that affects beef and dairy cattle. While the disease may not be obvious all the time, it can cause significant economic losses.

“BVD not only reduces fertility, it can lead to congenital defects and can lead to reduced immunity, especially in younger animals making them more susceptible to a number of other diseases such as pneumonia and scours,” explains Alasdair King, veterinary manager at Intervet/Schering-Plough. “In adult animals, immunosuppression can lead to more mastitis and even make stock more at risk from TB.

“Although relatively uncommon, Mucosal Disease is a form of BVD in which calves rapidly go downhill, usually dying within two weeks and there is no available treatment,” Mr King adds.  “However, most of the time, the effects of BVD infection in a herd are less obvious which can mean they go unnoticed and are even seen as ‘normal’ for that herd despite eroding profits.”

Unchecked and unseen, this disease can lead to significant economic losses – in beef herds, losses due to BVD have been put at £37/animal /year.

BVD causes most damage when it infects pregnant cows.  Foetal death, mummification of the foetus or abortion are possibilities at any stage of the pregnancy, but when infection occurs between 40-120 days into the pregnancy, a Persistently Infected (PI) calf can be born.  Studies show that 1 in 100 apparently normal cattle going through the abattoir are actually PIs so the chances are there is one in most herds.

What are the options

Option 1 is to do nothing, but who can stand losses this significant?

Option 2 is to maintain a closed herd with tight bio-security.   Individual blood samples must be taken to understand whether there are any PIs present and the herd, over time, will become naïve.  Should BVD re-enter the farm, the consequences will be significant as stock will have no immunity whatsoever.  Tight biosecurity includes double fencing all perimeters and maintaining a closed herd as key risk factors include replacements, hiring of bulls, and neighbouring cattle.

Option 3 delivers maximum financial benefit and is probably best practice – all cows and replacements prior to breeding are vaccinated.  This approach means there is sustained control of the disease and prevents the birth of any further PIs.  As with all vaccination programmes, the timings of vaccinations should be discussed with your vet.

Words courtesy of Farmers Weekly and Intervet Schering Plough