The Key to BVD: Understanding It
The best way to combat the ramifications of BVD is to understand the virus, how it affects you
and the warning signs.
Most people believe the symptom associated with BVD is diarrhea, while it can be a symptom most of the time BVD is subclinical, meaning you cannot visually see symptoms. In fact, the animal causing the problem may be the healthiest looking animal in the pen. This could cause a false sense of security for a producer who may not fully understand BVD.
In this article I will break down the symptoms, how the virus can affect the animal, how it can affect a cow/calf operation, how is can affect a feeding operation and how to protect against it.
Before I really get started, I want to clarify one thing: more than likely you won’t have the big “train wreck” catastrophe with BVD where 80% of your herd dies. These don’t happen very often at all. What really happens is you are quietly robbed of decreased gain, increased medicine costs, increased mortality and morbidity. Producers will assume they don’t have BVD because they haven’t had a big train wreck, yet.
First, a little about BVD. BVDv (bovine viral diarrhea virus) is an immunosuppressive virus, meaning it lowers the function of the animal’s immune system, making the animal very susceptible to common pathogens it could otherwise easily defend itself against. While diarrhea may be in the name of the virus, other common symptoms are pneumonia, gastrointestinal disease and reproductive failures, but 70-90% of the time BVD is subclinical, making it a hard virus to track down. Like I stated above, the PI animal is usually the healthiest looking animal.
What do I mean by PI? Well there are two types of BVDv infections. You can have an acutely (transient) infected (AI/TI) animal or a persistently infected (PI) animal. Acutely infected animals will have the virus for 7-14 days and then get over it, much like the common cold. Persistently infected animals are born with the virus and will have it for life, with no cure. PI’s are the root of the BVD problem we see today. AI animals may shed 100,000 virus particles per day for up to 14 days whereas the PI animal will shed billions of virus particles per day for their entire life, potentially causing mass herd health problems.
A PI animal is made when the mother is exposed to the BVD virus between 40-125 days gestation. The fetus is exposed to the virus, which at this stage does not have a mature immune system. The fetus will recognize the virus as apart of itself and not mount an immune response to the virus. The calf will continue to produce the virus in mass quantities until the animal dies. Most PI’s abort, some make it through pregnancy and die shortly after being born, a select few will live until slaughter weight/reproductive herd.
PI animals shed the virus through all excretions: manure, urine, saliva, nasal excretions, etc.
While PI’s are thought to have the biggest economic effect in stocker/backgrounder and feeding operations, they can also have a detrimental effect on cow/calf operations. Studies have shown that most PI’s are born to a non-PI cow that was just merely exposed to the virus. Any BVD-PI cow will always produce a PI calf. PI bulls can lead to many reproductive issues within the herd as well. Studies have shown that 10% of U.S. herds already have a PI in them!
So, what are some of the effects a PI can have on a cow/calf operation? Some of the costs include: increased abortions, lower conception rates, longer calving interval, higher prenatal and postnatal calf mortality, reduced weaning weight, increased mastitis, increased cow morbidity and mortality, less weight gain in calves.
That’s a long list. What can you do to prevent this from happening? Vaccinating your cows is a good tool as long as a PI is not in the pen. Vaccines work well fighting acute BVD infections, but a PI sheds so many virus particles that the virus essentially “over powers” the vaccine in non-infected animals. There are two options to check if your herd is BVD-PI free:
1. If you have already bred your cows, wait for the calf crop, there is no sense in testing before then as the damage will already be done if there is a PI. Test all calves, bulls and cows that didn’t produce a calf. If the calf is negative, the dam is negative. If the calf is positive, test the dam. It is possible the dam only had an acute infection then gave birth to a PI.
If you haven’t bred your cows, test all the bulls and cows.
This will give you a good snapshot of your herd BVD status. If you don’t have any PI’s, vaccines will work great. Why vaccinate if you don’t have a PI though? If you share a fence with another operation, BVD can be transmitted that way, it can also be transmitted through deer and mice.
Properly managing your herd health will not only help your profits, but help those down the line from your operation.
Here is where we usually see the biggest economic impact of BVD-PI animals and it all narrows down to co-mingling cattle. When cattle are kept in a closed herd they get used to their surroundings, including any pathogens floating through the air (like BVD). Once you introduce a bunch of naive cattle together, the effects of BVD become much greater.
Some of the costs to having a PI include: decreased gain, increased morbidity, increased mortality, increased medicine costs, increased management.
Here are some facts of BVD in stocker/backgrounder/feeder operations:
Reduced performance costs of $58
Increased medicine costs of $8
Just a few PI animals can expose 70% of a yard
PI’s are responsible for 43% of respiratory diseases
On average there are 3-5 PI’s per 1,000 head of cattle. This doesn’t sound like much but can amount to a 30%+ Incidence Rate by load. Learn more here.
To avoid sickness outbreaks, it is important to test all cattle upon arrival. Doing so is cost effective and does not slow down the processing of incoming loads. Studies have shown that testing all cattle can have a return of more than $20 per head.