Written collaboratively by Russ Daly, Christopher Chase, Travis Clement and Matt Dammen.
Bovine Viral Diarrhea Virus (BVDV) is among the most important pathogens affecting today’s beef and dairy cattle operations. Associated with reproductive, digestive, and respiratory illnesses in cattle, the virus can also create a congenital, persistent infection in calves, greatly aiding the virus’ spread within and between herds. Testing and removal of these persistently infected (BVDV-PI) calves is the hallmark of BVDV control and prevention.
How and why should someone go about testing animals for BVDV? Answers to those questions should start and end with the herd’s veterinarian – but some general information is good to have before that conversation takes place.
What are the possible triggers that indicate that I should test my herd for BVDV-PI animals?
Since BVDV causes so many different problems in cattle herds, there’s not one single tip-off that BVDV is present. Direct evidence might include abortions and infertility in the cow herd, or calves with birth defects. Mucosal disease, the end result of BVDV-PI illnesses, appears as sudden death, sometimes with acute diarrhea and ulcerations in the mouth and tongue. But the indirect effects of BVDV infection in a herd can also include suppression of the immune system, resulting in increased numbers of calves with pneumonia, scours, and other infections. Any of these situations could arise from BVDV circulating in the herd.
Finding evidence of BVDV in one of these animals – through a necropsy and BVDV test at a veterinary diagnostic lab – is a major indication of exposure, most likely from a BVDV-PI animal. Herd testing to identify and remove BVDV-PI animals is the key to preventing further related disease issues and keeping herd problems from multiplying by causing more BVDV-PI calves to be born.
What is the desired goal of whole-herd BVDV testing?
In cow-calf and dairy operations, whole-herd testing ensures that BVDV-PI animals are not present in the herd during breeding, where they could infect pregnant cows and create more BVDV-PI animals. Testing calves entering a feedlot will ensure BVDV-PI animals do not infect susceptible animals.
To accomplish this in cow-calf operations, attention needs to be paid to making sure the BVDV-PI status is identified for each animal present during the breeding season. Testing calves while nursing prior to the breeding season enables their removal before the breeding season, and can give an indication of the status of the cow. If a calf is confirmed to be BVDV-PI, its mother should be tested. All bulls, replacement heifers, and held-over open cows should be tested with no exceptions.
What samples does the lab need to determine whether BVDV is present in an animal?
Since BVDV-PI animals have virus throughout their body, a variety of samples can be used. From live animals, blood samples and ear notches are commonly used. In dead cattle, it’s best for the veterinarian to submit a complete set of body tissues to the lab, but ear notches can be useful as well if a complete necropsy is not feasible.
Can a BVDV-PI animal be confirmed on the basis of a onetime sample?
No. BVDV test procedures indicate the presence of the virus in the animal on the day the sample was taken. It’s possible for an animal to have a temporary (not persistent) infection with BVDV, through exposure to an infected animal or possibly through recent BVDV vaccination with live vaccines. A true BVDV-PI animal will be positive over time. An animal that tests positive for BVDV should be isolated from others and sampled again 3 weeks later. A BVDV-positive result on the second test confirms that the infection was indeed persistent. A negative result on the second test means the animal was only temporarily infected and, if clinically normal, should be able to return to the herd.
What should I do with an animal that’s confirmed to be BVDV-PI?
Since animals persistently infected with BVDV serve as a source of infection for other cattle and will eventually die from mucosal disease, they should be euthanized or – if of market weight – sent directly to slaughter as soon as feasible. Under no circumstances should they be kept in the herd or marketed to other operations.
What pitfalls should I be aware of when testing cattle for BVDV?
Some of the laboratory methods used to detect BVDV in an animal sample are sensitive enough to detect the virus from a vaccination. Therefore, it’s best to wait at least 3 weeks following BVDV vaccination before collecting samples.
Additionally, BVDV antibodies from colostrum in young calves could interfere with some tests. If testing calves less than 3 months of age, your veterinarian may have to adjust which specific test they request from the lab.
What is my best source of information about BVDV herd testing?
Your herd veterinarian. They will be able to take specific sampling and testing recommendations from the veterinary lab and apply it in the best way possible to your own operation. Asking questions and formulating a plan before any samples are ever taken will help ensure the results are valid and that your time (and money) is spent in the best way possible.