Cow virus 'not hard to control'
Getting rid of bovine viral diarrhoea (BVD) doesn't have to be difficult or cost the dairy industry $145 million, says the chairman of the BVD steering committee of the New Zealand Veterinary Association, Roger Ellison.
Speaking at the New Zealand Woman's Dairy Network conference, Ellison said BVD, a viral disease that can cause death in cows, had been almost entirely eliminated in some countries. However, in New Zealand it was present in about 15 per cent of herds at any one time.
"These animals are just more prone to some of the garden variety diseases," he said.
Ellison said infected herds had 5 per cent lower daily milking production, 2.4 per cent later conception and a 2 per cent higher abortion rate.
The cost of all this to a 400-strong herd was estimated at $94,000 a year, or $145m for the industry based on the current payout.
However, the disease was not difficult to get rid of, said Ellison, who had a herd devastated by the virus.
He said the key to controlling the disease was getting rid of any persistently infected (PI) calves as soon as tests showed they were infected.
These were calves which had picked up the disease at under 4 months of age in the womb, and whose immune systems subsequently failed to recognise and fight the disease. They remain infectious to other animals for the rest of their lives.
They were 22 per cent more likely to suffer severe illness or sudden death, grow 18 per cent slower than non-PI calves, and had a 17 per cent higher death rate at 2 years. Ellison said the calves needed to be eliminated as early as possible, to avoid continuing infection for the rest of the herd.
"Prevention is the key," he said.
"Screen all calves at a young age. Vaccinate the replacement heifers."
Ellison said the estimated cost of keeping a herd of 400 cows with 25 per cent replacements BVD-free would be about $4000. That was a small cost compared to the $94,000 of harm possible if the disease ran through the herd.
The cost of clearing the equivalent herd of BVD was estimated at between $7000 and $13,000.
Ellison said TI (transiently infected) calves were likely to show few signs of the disease unless stresses were present. If stresses were present there could be an impact on growth rates and long-term health.
Making sure the infection was dealt with as soon as it was discovered was, therefore, important.