BIOSECURITY has been a buzz word for veterinarians ever since I started in practice many years ago. Maybe we didn’t refer to biosecurity using the same terminology we do now, but since the 1950’s when tuberculosis and brucellosis eradication were in full swing, testing every cow that was sold, purchased, moved, or shown, was routine. We had to know the disease status of mobile animals, especially for TB and Bang’s.
I have written about leukosis and Johne’s disease in two previous Cowside Practice columns. Both are diseases dairymen need to consider before purchasing cattle and bringing them into the home herd.
Also, it is a good idea to determine the incidence of these two in your own herd. You need to be vigilant to see that they do not increase in incidence but decline in importance.
There is another disease that is lurking at your parlor door, BVD, bovine viral diarrhea.
My impression of the disease has changed dramatically from the time I recognized it
Today, I still see some of these forms, but I know now that BVD is a reproductive disease with abortions and infertility the result.
When Russ called, he was quite disturbed. On this particular Saturday morning, he told me that tetracycline had no value in treating five of his cows. Their temperatures were at high as 106°F during the previous week. I knew he could be experiencing an acute BVD outbreak.
During the next few days, virus isolation confirmed my suspicions. Fortunately, Russ had been on a constant vaccination program with a modified live virus vaccine in his heifers. The yearly booster for the milking herd had been with a killed vaccine. He experienced no death losses. However, he suffered production losses.
Russ has an excellent grade Holstein herd. He had lost three heifers at freshening due to calving paralysis, blind quarters, and mastitis. He needed replacements, so he purchased five springing 2-year-olds at a sale barn. One had BVD; Russ brought the virus to his farm.
At our local veterinary meeting, a colleague told about one of his clients whose herd recently had experienced several abortions. His client, too, had purchased three bred heifers. Blood samples from several acute and convalescent animals revealed high titres to BVD.
My veterinary friend decided to test the herd for persistently infected, noncytopathic viremic animals. One of the purchased heifers was the culprit. She had shed the virus and spread BVD. Again, BVD was an uninvited guest and brought to the farm in an untested animal.
No, BVD is not easy to recognize. Nor is the disease easy to identify. But we do have the tools to find the answers.
The insidious nature of the disease does make it difficult to make a diagnosis. You can get a tip as to what is wrong if there are some abortions followed by calvings which result in weak calves and congenital deformities. Even then, diagnosis by a laboratory is difficult.
When an animal is challenged by the virus, it only remains viremic for a few days; you fail to find the virus later. However, you can isolate the virus from the aborted fetus.
The virus can be spread in semen. Bull studs take great care to make sure their bulls are free of the virus. In embryo transfer work, make sure donors and recipients are free of the BVD virus.
I cannot cover all aspects of the disease. I’m only trying to make readers aware of the disease. It must be dealt with in a biosecurity program.
Vaccinate your heifers for BVD and provide a yearly booster to milking animals. Follow the advice of your veterinarian. He or she will choose a regimen that fits your herd.
If animals are ill, test all animals by virus isolation, and check for persistently infected animals that could be the source of the virus. Be sure to test all show animals. The key is to maintain your herd free of persistently infected individuals so that no virus will be shed and spread to other animals.
Reprinted with permission from HOARD'S
DAIRYMAN
Written by L.C. Allenstein, D.V.M.