June 2016
From the State Vet's Office

Bovine Viral Diarrhea Virus

What You Don’t Know Will Hurt You

Viruses are funny things – not humorous funny but more unique funny. You can’t see them with a normal microscope. They are not really living things, but I think they are mostly considered to be living – even though they don’t necessarily meet all the qualifications to be an organism. Viruses are just a little strip of genetic material, RNA or DNA, covered by a protective coat. A virus requires cells from a host animal or plant to even replicate. What happens is really like a hostile takeover. Take a virus that causes the common cold, for example. The virus invades the cells of your upper respiratory tract, takes control of the cells and forces the cells to produce bunches of new virus particles. This damages the cells of your upper respiratory tract and generally makes you feel bad. There is a lot of other complicated stuff that goes on, but we won’t go into that in this article. In this column, I just want to focus on one of those viruses that is a significant problem in the cattle industry. That is the bovine viral diarrhea virus. (By the way, the word virus has Latin origins going back to the 14th century and had the meaning of poisonous substance.)

The BVD virus was first associated with mucosal disease back in the early 1940s. Mucosal disease is a condition characterized by diarrhea, often bloody, followed by dehydration, loss of weight and death. In the past three-quarters of a century, we have gathered vast amounts of knowledge about the virus. But it seems for each question we answer two or three new ones are asked. The answered questions tend to show that BVD is likely more prevalent than we had thought in the past. When I was in college, they were beginning to make some decent strides toward finding persistently infected calves that were the reservoirs keeping the virus out there in such numbers. Hopefully by the time you finish reading this article, you will appreciate the significance of persistently infected calves and the potential for sizeable negative economic impact on the cattle industry.

I have always heard that the difference between a recession and a depression is all about perspective. If your neighbor loses his or her job, it is a recession. If you lose your job, it is a depression. I think the same thinking applies when it comes to BVD in cattle. If someone else has to deal with it, it is an economic setback. If you have it in your herd or stocker operation, it is financially devastating. Last year, when the cattle market was at historic highs, some of our lab folks told me about some producers dealing with BVD. I would have to say, if I had been them, that I would have at least lost sleep over the problem.

There was a stocker grower having an outbreak of pneumonia and he was losing the battle most of the time. After losing six or eight of his $1,200-a-head stockers, the lab got involved and found that he had a persistently infected calf in the group.

Another producer lost four calves that were either stillborn or died a day or so after birth. The producer took loss No. 4 to the lab and found it was a PI calf.

Dr. Terry Slaten, at the Hanceville Lab, tells me that he is now able to present a little bit of a positive side to having BVD in the herd when he informs the producer. He says the bright side is that the producer’s potential loss is quite a bit less this year since the cattle market has dropped. I am not sure how consoling that is to a producer losing calves.

I want to say a little about PI calves and why they cause so many problems. PI calves are a result of a cow being exposed to a certain strain of the BVD virus while the calf in her womb at 40-120 days of development. That is significant because the calf’s immune system is not yet developed. So, if the virus moves in and is established in the calf’s body before the immune system develops, the immune system thinks the virus is just part of the calf – like its ears, tail or heart. Most of these calves die in the womb or do not live long after they are born. However, there are a small percentage of these calves that live. Some of these PI calves are poor doers. A very few of them may not appear to be sick for a long time, although they usually get mucosal disease and die by the time they are 2 years old.

One problem coming with PI calves is that they shed millions of virus particles in every body fluid they produce. That becomes a huge problem with cattle in feedlots because having a PI calf in a pen of other cattle exposes them to constant high numbers of the virus. Even if the other calves in the pen do not get clinically ill, they will not perform nearly as well since their immune systems are working overtime because of the constant bombardment from the virus.

Many of the PI calves that live long enough eventually get mucosal disease, as I mentioned earlier. We have found exposure to the PI calves result in reproductive problems in the brood cow herd and severe suppression of the immune system, leaving the cattle susceptible to any number of other diseases. At the very least, exposed cattle do not gain weight and perform to their potential. So if you are unlucky enough to have a PI calf in you pasture, the downside possibilities are numerous. The upside possibilities are … well, zero.

We have reactivated a BVD working group that involves several entities in the veterinary and cattle industry to see what can be done to reduce the number of PI calves in the industry. I intend to have more information in future columns about the progress and direction of this working group. In Europe, BVD is a regulated disease. Some states in the United States are developing their own regulations to take PI calves out of commerce. We are not necessarily on that track, but are looking at ways to help the industry deal with and reduce the negative impact caused by BVD PI calves. Stay tuned.

Dr. Tony Frazier is the State Veterinarian for Alabama. You can contact him at 334-240-7253.