“In the absence of circulating virus or vaccination, natural protection wanes. Therefore, when BVD enters a naïve herd or a herd that was previously clear, the results can be devastating,” said Donal who runs Donal Lynch Veterinary at Killurin, outside Tullamore.
According to the latest figures from Animal Health Ireland (AHI), of just under 1.5m calves tested in the first 18 weeks of this year, a total of 677, or 0.05%, have been considered to be persistently infected (PI) with BVD virus.
The number of calves considered to be PI for the first 18 weeks in 2017 was 1,381, or 0.09% of just under 1.5m calves tested.
AHI figures also show that, for the first 18 weeks of this year, one or more PI calves were retained on 36 herds for five weeks or more after the date of the first test. During the same period in 2017, 64 herds retained one or more PIs for five weeks or more after the first test.
“While overall these figures are encouraging, farmers should not allow themselves to be lulled into a false sense of security,” warned Donal Lynch, who has direct experience of the horrendous impact of BVD breakdowns.
The most dramatic example is of one of his dairy farmer clients who had one PI last year. This year, that same farmer had 17 PIs.
Another example is of a client who visited his practice in recent weeks. He was purchasing a supply of leptospirosis vaccine. Donal enquired if he was also going to vaccinate against BVD.
The farmer told him he had stopped the BVD vaccine a couple of years ago as he was clear of the disease since 2012. Two days later, he got a call from the farmer telling him that he had just got word that a calf had been identified as a PI. The farmer is now back vaccinating.
“In some cases, PIs are not got rid of until the calf is at least seven weeks old.
Up to 60% or more of the herd could calve during that period, hugely increasing the risk of transient infection. When a cow or heifer is exposed to the virus during the second to the fourth month of pregnancy, a PI calf is formed,” said Donal Lynch.“PIs should be isolated and disposed of as rapidly as possible.
“They shed 1,000 times more virus than transiently infected animals. Transiently infected and suspect animals should also be isolated and purchased cows, heifers and stock bulls should be quarantined.
“Even when a PI animal is removed this does not mean that the herd is free of BVD.
“Equally, where no PIs are identified and where a closed herd policy and strict bio-security measures are operated, there is still a constant risk of infection from neighbouring herds or on equipment and people.
“I also urge annual vaccination. Because of the multitude of methods by which the BVD virus is transmitted, vaccination remains an absolute necessity on every farm until we rid the country of this disease,” he stressed.
Bovilis BVD vaccination advice
Vaccination combined with identification and removal of PIs, good bio-security and ongoing monitoring are crucial in controlling BVD, said Cara Sheridan, ruminant veterinary advisor with MSD Animal Health. “Two injections of Bovilis BVD, given four weeks apart, are needed as a primary course in non-vaccinated cows and heifers.
“The second vaccination should be given at least four weeks before breeding. All vaccinated animals should then get their annual booster four weeks before breeding,” she said.
She highlighted the importance of using a vaccine that is licensed to provide foetal protection.
When administered at the correct time pre-breeding, Bovilis BVD will provide protection to the foetus during the risk period.
Combined BVD and IBR vaccination
Animals can be given a combined booster vaccination against BVD and IBR (Infectious Bovine Rhinotracheitis). This means that Bovilis BVD and Bovilis IBR Marker Live can be mixed together and given in one single 2ml intramuscular injection. The combined vaccine should be used as a booster dose in cattle from 15 months old, helping to simplify vaccination against two of the most important diseases on Irish farms. Talk to your vet about best practice in administering the combined booster vaccine.
Cattle more prone to attack
“While BVD is not the big risk that it was, cattle are going to be more and more naïve, making them much more prone to outbreaks,” said veterinary practitioner Donal Murphy who runs the Sliabh Luachra Veterinary Centre at Rathmore, Co Kerry.
He has seen a dramatic reduction in the number of PIs on his client farms in recent years. While he has no direct experience of new outbreaks, he is “not at all surprised that these are occurring in other parts of the country.”
“The results of blood tests we carried out on young stock towards the end of last year showed that a number had been exposed to the BVD virus. This is a worrying development as it shows that the BVD virus is still circulating in herds.
“A few years ago, BVD was the big, bad, evil disease. Farmers have now become blasé about it. My advice is to still treat it as a big risk and take all necessary precautions to avoid a fresh outbreak,” said Donal.
He said that the level of vaccination has reduced significantly in recent years, with farmers feeling that if they don’t have the disease there is no need to vaccinate.
“I strongly advise that vaccination is still a vital part of the BVD control strategy on every farm. It’s a small cost compared to the stress and financial loss resulting from an outbreak,” he said.