Managing the BVD virus, a silent killer

COVID-19 might be on the minds of just about every American right now, but another virus has been and continues to cause issues for cattle producers. Bovine viral diarrhea is caused by the bovine viral diarrhea virus. Although diarrhea is in the name, Dr. Bruss Horn, DVM, and owner at Verden Veterinary Clinic in Verden, Oklahoma, said this is actually a misnomer, because diarrhea is not actually a symptom.

Instead, the virus suppresses cows’ immune systems, attacks their lymph nodes and white blood cells. Symptoms can include: ataxia, tremors, wide stance, pneumonia, weak or dead calves at birth, abortions, deformed calves, delayed or strung-out calving periods, increased number of open cows, death post weaning, stumbling and failure to nurse. The wide range of generic symptoms makes the virus difficult to pinpoint. Calves that contract the virus in utero are known as persistently infected or PI because there is no treatment and those animals will carry it the rest of their lives.

“Calves become PIs when you’ve got a momma cow and she’s 30 to 120 days pregnant and she gets exposed to BVD virus, it gets in her blood system and it transfers to the calf,” Horn said. “When he’s born, grows up and becomes a five-weight steer, he sheds millions of virus particles daily, thus exposing multiple cattle to the potent immunosuppressant virus.”

The virus is extremely contagious and Horn said if there is one positive animal in the pen, it will affect every other animal in contact with it. Horn said in some cases, it is impossible to tell a positive PI calf from a negative animal. PI calves are often poor doers and symptoms may become noticeable over time, but by then the virus has already spread. He said positive calves can sometimes live to 6 to 8 years old and never become poor doers, although they are still shedding the virus at the same rate as PIs with symptoms.

So what about cattle that are exposed in utero after the 120 days? Horn said at this point, the fetus has developed enough of an immune system that it can fight off the virus. It will not be a PI, but it will be congenially infected or a CI calf. A CI calf  will not shed the virus, but it will probably be a poor doer.

The virus can also affect BVD vaccinated cattle that are exposed to the virus and they can become transient infected or TIs. Horn said the virus overwhelms their immune system, however, they will not carry the virus and shed it the rest of their life like PIs. The majority of TI cattle will get over the virus, but some will not.

Cattlemen’s guide to a BVD outbreak

BVD is not a heavily covered topic partly because it does not occur at the same rate as some other ailments like bovine respiratory disease. Horn said the incident rate of PI BVDs in the United States is 0.25 to 1%, which sounds miniscule, but that means one animal in 100 or 400 is going to test positive. And in fact, the percentage could be even higher because Horn said he sees higher numbers at his clinic.

“At our clinic we find more than that, with stocker calves I believe it is closer to 2 to 4%,” he said. “You’ve just got to remember that that one calf is going to affect several hundred head of cattle out there.”Horn said cattlemen can work through a PI BVD storm, but it will take several years. The first recommendation is to test animals that could be infected. The most common way of testing is ear notching, but blood can be used to obtain results. Horn said disinfecting between testing of calves is critical to get accurate testing results. He said he is always suspicious when two or three calves in a row test positive for the virus.

So what do you do if you have an animal that tests positive? The first step is to remove the animal immediately and keep it from infecting any new animals. Horn said if one calf is suspected of having BVD and tests positive, he recommends testing every calf immediately to remove any that are already infected and could spread it to the rest of the herd. He also said if you have a positive calf, he recommends testing the cow and cull her.

“A negative cow that has a TI status can give birth to a positive calf, but a positive cow will always give birth to a positive calf,” Horn explained. “I haven’t found many positive cows, but they are out there.”

Once a calf tests positive, there are several options. Horn said Texas recently passed a law making it illegal to sell a positive PI calf and he expects to see more legislation on this subject in future. However, some states like Oklahoma, have no laws against it.

“In Oklahoma you can take a PI calf to the sale barn, but the problem with that is then it could be shedding the virus and affecting more animals,” Horn said.

Horn said PI cattle can be fed out and in fact he has done it several times, although he said it is difficult to get them over 1,000 pounds because of the effects the virus has on their body. He said if you sell a PI calf to be fed out, be sure to make any buyers aware of the PI status so they can keep the animal separate from their herd. Additionally, although when a PI calf has the virus, it has it for life, Horn said he does not condone comingling positive animals because there are different types of the virus such as 1A, 1B, 2A and 2B, and they can cross infect each other and die even sooner.

So what is the solution to protecting herds for this virus? It all adds up to a combination of testing and culling animals, enhanced biosecurity and vaccinations. Right now, there is a modified live and a killed virus vaccine. Horn said producers need to be careful not to use fetal protection vaccines on pregnant cows because they are modified live vaccines. Proper vaccination protocol protects the cow and calf from and decreases the number of PI calves. BVD may pale in comparison to the coronavirus of 2020, but it will continue to plague herds that are not protected or cattlemen that are unknowingly spreading it to their calves. If COVID-19 has taught us one thing, it is that viruses can spread like wildfire and you do not want to be stuck in the epicenter of an outbreak and neither should your calves.

Lacey Newlin can be reached at 580-748-1892 or [email protected].