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Vet Talk: Persistently Infected Bovine Viral Diarrhea Virus - Why is it a problem?

Dr. Don Coover, DVM, SEK Genetics

I am often presented with a producer that finds he is having trouble with open cows, “poor doing” cows or sick calves, cows with lower than expected fertility, or other non-specifiic production problems. While these problems can be due to a lot of causes (like poor nutrition, stressful conditions, ect.), I am always concerned about animals in the herd that may be persistently infected with a BVD virus (or PI BVD).

Most producers recognize when their cattle are suffering from stressful conditions like drought or cold muddy conditions that limit production goals. These conditions are obvious. But when a herd is suffering the consequences of having PI BVD animals in their midst, the cause for all these production losses is anything but obvious. Many PI animals appear healthy, are in good flesh, alert, and apparently normal. The problem is that PI animals shed enormous quantities of the BVD virus continuously, infecting and re-infecting their herd mates as long as the PI animal is alive. While it is true that PI animals appear healthy, at least for a while, many of these PI calves will die before one year of age. Some will survive much longer.

Recently, a producer brought in 8 heifers for us to AI. We synchronized the heifers, caught heats and AI’d them to expensive bulls. I asked the producer about testing for Neospora and PI BVD but he did not want to spend the money and he vaccintated his whole herd for BVD annually.

After AI’ing, the heifers, we sent them home, confident that we should get good results. At 35 days of gestation, the producer pulled blood and sent it in to us to run a pregnancy test. Only one was pregnant. I immediately suspected a problem and asked the producer to BVD test the calves that were around the heifers. He said “No”, saying they had already spent enough on the AI project. Since I still had the blood, I had the lab tech test the samples for BVD. One of the eight was a persistently infected with BVD I am confident that was the reason we had such poor results on the AI project. Since then, we showed him the results and he has tested the rest of his herd, finding 2 more PI animals of the 60 cow herd.

The point is, even good producers can have a significant BVD problem and not know it. The only way to be sure that you do not have BVD issues, and the losses associated with BVD, is to test for it.
I strongly encourage producers to test all animals in their herd for BVD, directly or indirectly, and any new animals. You only need to test each animal once since they are born with it and cannot become a persistently infected after birth. Another thing to remember is that PI cows ALWAYS have PI calves but most PI calves come from “clean” cows.

BVD is a virus that is strongly immunosuppressive, and is a common cause of abortion and makes cows more susceptible to other illnesses like respiratory disease, scours, pinkeye, foot rot, and so on.
Vaccinating with a good BVD vaccine is a good herd health practice, but you cannot vaccinate your way out of an existing PI BVD problem. A BVD vaccine is a good insurance against developing a problem, but testing is the only way to be certain that you don’t have a problem.

Here is a good 3-step program to control against BVD:

1. Test all of your herd, directly or indirectly. If you know which calf goes with which cow, test the calves. If the calf is negative, the cow is negative. If the calf is positive with BVD, test the cow.

2. Test all the bulls, new additions to the herd, and all newborn calves (including stillborn calves or young calves that die which have not been tested).

3. If you find a PI, remove it from the herd immediately and work with your vet to develop a plan to clean up your herd.

I test all my calves, and everything I buy, raise, and sell for PI BVD. The test you use is important, also. I strongly recommend against “pooling” samples to save testing costs. “Pooling” samples dilutes the sensitivity of the test.
PI BVD is a problem we see often here at SEK Genetics lab. We do a lot of testing for it from producers all over the country. We test ear notches, whole blood, or serum. The average incidence of positive samples runs about 1%-4% per hundred. Even this very low incidence causes lots of problems in herds because of the positive animals shedding so much virus.

The cost of testing for BVD at SEK Genetics is $3.50 per sample. We use a USDA licensed ELISA test made by IDEXX. You only need to test the animal once. A PI animal is born with it and they die with it. Negative animals are always negative. The animal is infected as a fetus.

If you have additional questions about PI BVD animals, or programs to guard against developing them in your herd, contact me, Dr. Don Coover, DVM, at SEK Genetics: 620-763-2211. If you want to arrange for testing or sending samples in for testing, contact the office staff at the same number or find more information at SEKGENETICS.COM.

 More Vet Talk: Heifer Replacement 
 More Vet Talk: Neospora Infections 

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