Dealing with local cattle diseases

Bovine viral diarrhea (BVR) is estimated to infect 4 to 10 percent of local cattle, Dr. John Currin of the Virginia-Maryland Regional College of Veterinary Medicine recently told a group of Augusta County farmers.

Dr. Currin said that besides the actual death of an infected animal, the real loss with BVR is ensuing long-term problems with reproduction, poor condition and the threat of an infected cow passing the virus to her calves and herd-mates.

Noting that an infected cow usually "either dies or gets better on its own," the vet added that BVR is a viral disease that not only spreads easily from cow to cow, but mutates readily, assuming new forms.

Infected cows shed the virus continually in manure "24-7," he said. Some infected cows not showing noticeable symptoms are known as "persistently infected (PI)" and remain so throughout their lives.

Dr. Currin explained, "The virus tricks the immune system into thinking that it should be there in the body, so the immune system does not attack it."

Because the immune system does not fight the virus, the animal is more susceptible to other ailments, especially respiratory illness.

Bulls also can be infected and spread the virus to cows, so herd bulls, especially those newly purchased, should be tested, he advised.

Among symptoms of BVR are ulcers in the roof of the mouth and among birth defects in BVR calves are those born with "abnormally small eyes," Dr. Currin added.

While most BVR calves die by their first year, he said those that survive and go into feed lots continue to do poorly, gaining less weight but requiring more medicine and are less efficient at converting feed into pounds of meat.

In dealing with BVR, Dr. Currin said bio-security is important as a control, especially when buying replacement heifers. He cited one farm that bought a teaser bull to detect heats. The buyer didn't know that the bull carried BVR. "It was a really big mess to get it under control," he said.

Like most viruses, BVR does not survive long outside the body, so it is unlikely that other cows contract it from streams in pastures. "Much more likely is direct contact between cows, such as nasal secretions of infected cows," he noted.

As for control of BVR, he said the only effective way to eradicate it from a herd is to test for the disease and destroy infected animals. "You can't vaccinate enough to control it," in his opinion.

A cow that tests negative should be isolated and re-tested in three weeks. If an animal tested postive the first time, it could be what is termed "transitionally infected" and re-tested in three weeks.

Dr. Currin said, "If it is still postive, don't pass the animal to someone else-that is unethical. Instead, destroy the animal."