Controlling bovine viral diarrhoea

Effectively controlling Bovine
viral diarrhoea virus (BVDV) in cattle herds takes an integrated farm biosecurity system. This includes keeping farm fences in good condition and limiting the movement of unauthorised people and cattle on and off the farm. But a pillar of any system should be a comprehensive vaccination programme.

- Advertisement -

At a beef symposium held at the Dundee Research Station in KZN, Dr Martin Ferreira, a vet from Potchefstroom in the North West, said it’s important to vaccinate whole herds against BVDV, and to correctly handle and use BVDV vaccines.

According to the website, BVDV is very infectious agent and can contribute to many cattle diseases, affecting the reproductive, respiratory and immune systems. There’s a Type 1 and a Type 2 BVDV virus. Type 1 erodes the animal’s health more gradually, while Type 2 can cause sudden death. Dr Ferreira says a BVDV vaccine brand that contains effective protection against both types is best. The vaccine must also give foetal protection to prevent the development of permanently infected (PI) cattle. PI calves are born from pregnant cows that have been infected with BVDV between 45 days and 125 days of pregnancy or which didn’t have protective immunity against BVDV, which then passes to the foetus.

A BVDV vaccine should also protect against other viruses, like infectious bovine rhinotracheitis, parainfluenza and bovine respiratory syncytial virus.Herd profitability is most threatened by the Type 1-infected cattle that are quietly, but significantly, underperforming. Of a herd’s existing PI animals, 90% are the offspring of pregnant cows that were infected with BVDV but that had no foetal protection immunity. The only control for PI animals is to permanently remove them from the herd.Julia Ridpath, a US microbiologist specialising in ruminant diseases, likened the effects of BVDV to be being nibbled to death by a duck. “BVDV is a very complex disease, and Type 1 is a slow and methodical killer,” she explains.

- Advertisement -

When and how to vaccinate
Dr Ferreira warns that vaccinating only part of a herd against BVDV won’t help. “BVDV infection is very stress-related,” he explains. “Ideally, BVDV vaccinations must be used before expected stress periods like late winter. Vaccinating under stress conditions can cause the immune reaction to the vaccine to be undesirably weak.“But BVDV is especially prevalent in late winter when natural veld and water are at their lowest and cattle’s stress is highest. To minimise stress and to get the best value from your vaccine, give a Multimin injection one month before vaccination.

Pregnant cows and calves
Dr Ferreira explains that BVDV vaccines are either dead or modified live (attenuated live). “Dead vaccines are safe to use in pregnant animals and there’s only an abortion risk if modified live vaccines are used on animals that weren’t correctly vaccinated before their first pregnancy. Consult your local vet for more advice if you have any doubts. “Be careful of unproven BVDV vaccines. They may be cheaper, but if they don’t work properly, you’re going to lose much more money from sick and dying animals.” He also warns that recent media reports, indicating that calves must be vaccinated against BVDV at between 10 and 14 days old, are a marketing ploy. Calves from cows that have been vaccinated with a BVDV vaccine that gives foetal protection will only lose their maternal resistance to Type 2 at 114 days, and to Type 1 at 140 days. Vaccinating such a calf kills off this resistance.He says a calf should get its first BVDV vaccination at five months old, with a repeat vaccination 14 days before weaning, to help it during the stress period of weaning and the change of nutrition.

Replacement animals
Replacement animals should have had two to three doses of a modified live BVDV vaccine before their first pregnancy, and thereafter a yearly booster BVDV vaccination. For cattle that have never been vaccinated against BVDV before, Dr Ferreira recommends that pregnant females be vaccinated with a dead vaccine, and non-pregnant animals with a modified live vaccine.Contact Dr Martin Ferreira on 082 801 2835, or e-mail [email protected].     |fw