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Why Test for Cattle Persistently Infected With Bovine Viral Diarrhea Virus?

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PI and BVDV. By now, most cattle producers have at least heard these "buzz words." If you've picked up just about any trade publication, been to an industry meeting or talked to a Noble Research Institute livestock specialist, you've probably seen or heard the terms before persistently infected (PI) bovine viral diarrhea virus (BVDV). Yet, there are still some who have not received, or don't fully comprehend, the message.

What is the concern about?

According to Robert Fulton, DVM, of the Oklahoma State University College of Veterinary Medicine, the prevalence of PI cattle in the U.S. population ranges from 0.13 percent to 2 percent. About 4 percent to 10 percent of U.S. beef herds will have at least one PI-positive animal. Briefly, Fulton states that a PI animal is one that was infected with BVDV between 45 and 125 days of gestation. This is the only way to become a PI animal. Most PI-positive cattle die shortly after birth, but a significant number live to make it into the breeding herd or the feedlot. Herein lies the problem a PI-positive calf is constantly shedding the virus and exposing the healthy animals around it.

There are two typical ways a fetus can become a PI animal through either vertical or horizontal transmission. Vertical transmission basically means the fetus is directly infected from the dam that is a PI animal. A PI cow will always have a PI calf. Horizontal transmission of the virus is probably more common. It involves the exposure of a bred cow to BVDV during the critical 45 to 125 days of gestation, either from a suckling calf, a PI-positive cow or bull in the herd or across the fence or a neighbor's sick calf infecting the fetus though contact with the dam.

CalvesCan you tell if any of these calves are persistently infected with BVDV?

Why the concern?

So, now that we have a basic understanding of what the problem is and how it replicates, why is the industry only now confronting this problem head-on? Because it has become a documented financial consideration. A March 2006 article in BEEF magazine, written by Clint Peck, estimated the cost of one PI animal in a cow herd ranges from $14.85 to $24.84 per cow per year. The cost estimates include reduced weaning weights, illness, death loss of newly born calves and the silent factor of open cows that cannot be explained otherwise. Without testing for BVDV, you don't know if you are one of the producers who is losing money every year and not realizing it. Additionally, there have been reports of order buyers paying at the upper end of the market for cattle with documented PI-negative status.

Producers now have at their disposal a cost-effective and easy testing tool. All that is required is for an ear notch to be taken. From this sample, a diagnostic lab can determine if the animal is PI or not.

How do you control PI BVDV in your herd?

BVDV control is fairly straightforward and requires a plan that includes testing, vaccination and management. If possible, test your calves prior to bull turnout. Identification and removal of a PI-positive calf at this stage will prevent it from infecting a fetus in utero for next year's calf crop. If you get a positive calf, test the dam. Make sure she is not a PI cow. If you have a PI-positive animal, the only ethical thing to do is to send it straight to slaughter or destroy it. Also, test all replacement cattle coming into the herd, including bulls and females. Require the ranch you are purchasing cattle from to test prior to purchase. Don't turn out new cattle until you have the test results and a quarantine period has been cleared. A comprehensive vaccination plan should be designed with the consultation of a veterinarian. Vaccination of the herd will help reduce the chances of having a BVDV outbreak. Vaccinating will increase protection of your herd against other cattle they come in fence-line contact with. Vaccination and testing for PI animals must be integrated. If you aren't doing both, you are compromising the entire system.

Here at Noble, we believe in the benefits of testing so much that we test any incoming animal, be it a stocker or a replacement bull or female. We also are making this a condition of the purchase of any cattle we facilitate for a producer. We have developed the philosophy of "No test, no sale."

Three Critical Control Points for PI Control
  • Diagnose and remove PI cattle from herd
  • Vaccinate for BVDV
  • Implement a biosecurity program for all replacement animals

Robert Wells, Ph.D., PAS joined the Noble Research Institute as a livestock consultant in 2005. He also serves as the Executive Director for the Integrity Beef Alliance, LLC. His areas of emphasis are forage-based beef cattle production and cow/calf nutrition, herd health programs, improving herd genetics, beef quality assurance, and value-added calf marketing programs. Wells grew up on a South Texas diversified farm and attained his Ph.D. from the University of Illinois. You can follow him on LinkedIn.