This information is brought to you by BVD Zero.
BVD (bovine viral diarrhoea) is the most common viral disease of cattle in Europe, yet is something which appears to be tolerated by many producers, perhaps because the disease is hard to spot.
Studies show vets believe in excess of 80 per cent of cattle (dairy, suckler and beef) are at risk of the disease and would benefit from being looked after with some kind of on-farm BVD management programme.
Denmark, Sweden and Norway started BVD eradication programmes about 20 years ago and can now be described as BVD free. Eradication programmes have also been launched in Germany, Scotland, Ireland, parts of Belgium and the Netherlands and, most recently, the Isle of Man.
Rob Drysdale, of Westpoint Vet Group, says: “In England, DairyCo, Eblex and the NFU have been behind an initiative called BVD Free which, although not mandatory, encourages farmers to work with their vets to understand their BVD status and take appropriate action.
“Part of the programme has provided funding for vets to hold farmer meetings and undertake various herd investigations. Backed up by a practice’s own BVD initiatives, this will doubtless have led to more virus being detected and control programmes being put in place,” he adds.
Globally, there are two types (genotypes) of the BVD virus; BVD type 1 and BVD type 2. The incidence levels of both vary across the world: BVD type 2 represents about 50 per cent of cases in North America, whereas BVD type 1 dominates in Europe.
“While BVD type 1 can go unseen in a herd for months or years, BVD type 2 commonly leads to severe disease with significant levels of cattle mortality,” Mr Drysdale explains.
“Luckily, BVD type 2 is not endemic in the UK at present, although there was a warning last summer issued by AHVLA outbreaks had occurred as close as Belgium. With the amount of cattle trade between the two countries, vigilance was urged.”
Looking at BVD type 1, affected animals show very different symptoms and there is often a delay between virus exposure and the clinical effects.
“BVD is particularly dangerous when infecting pregnant dams. If a pregnant dam is exposed to the virus at between 42-100 days gestation and the calf is born alive, it will be a PI or Persistently Infected calf,” he says.
“PIs are capable of shedding virus into the herd and although often unthrifty, can live to produce a calf of their own. They are the most common source of virus, and therefore infection, in a herd.”
“A lot of eradication schemes stipulate PIs are immediately culled once identified,” Mr Drysdale says.
“This approach, coupled with ensuring all stock sold or traded are of known vaccinal status, backed up with quarantine and bio-security, is an approach which worked well in the Nordic countries. Interestingly, these countries and others have not stipulated vaccination as part of the programme.”
In the UK, it could be reasonable to ask why vaccination alone is seen by many as a method of control, when the available vaccines have to be used under strict protocols which often sees them being mis-used on-farm. Two studies have shown widespread issues around timing of the second dose in the primary course, and the timing of boosters is frequently far from stated protocol.
“Veterinary input to manage BVD is vital if a farm is to get the most from the programme,” says Mr Drysdale.
Without mandatory Government guidelines, control and eradication will always be a challenge. A recent report on the Irish eradication scheme stated an alarming 30 per cent plus of PIs are kept on-farm even though they have been positively identified. Enforced culling is not an element of the Irish control programme, meaning individual farms can act as they see fit.
In contrast, the main theme of the Isle of Man BVD control strategy is PI identification and removal and the scheme has moved from a voluntary to mandatory phase. More than 80 per cent of calves born in the last year have been tagged and tested and the legislation now means PI animals may not be moved anywhere other than direct to slaughter.
“At Westpoint, we have developed a BVD protocol using screening for and identification of PIs, culling, vaccination and bio-security. There is also ongoing testing for farms to ensure compliance while minimising future risk.”
Interestingly, a survey in Europe looking at data from the 1970s to the present, shows BVD is endemic in all countries where no systematic control has been initiated. Under such conditions, about 50 per cent of herds have PI animals, and 90 per cent of cattle become exposed during their lifetime.