Feed Lot Magazine Online, BVD Skin Test Helps Producers Detect Disease Earlier

A test for Bovine Viral Diarrhea (BVD) introduced by a University of Nebraska veterinary scientist that helps cattle producers identify the disease sooner is generating a good deal of interest. The test is accurate even for calves soon after birth, allowing earlier detection of persistently infected animals.

" We 're doing 800 to 900 tests a month now and samples are coming from all over the U.S.," said Bruce Brodersen, veterinary pathologist at NU's Veterinary Diagnostic Laboratory. "We're finding a few positives."

BVD is a serious cattle disease, causing estimated losses of up to $150 million annually nationwide. Symptoms range from mild to severe diarrhea. BVD also suppresses the immune system, which can lead to other bacterial and viral infections.

Persistently infected animals aren't common but can be difficult to detect, and a single case can be devastating. "You can lose up to 10 percent of calves born in a herd from severe diarrhea and concurrent infections if a persistently infected animal infects others," the NU Institute of Agriculture and Natural Resources scientist said.

The BVD virus spreads from animal to animal in a herd. When a pregnant cow becomes infected at between 80 and 150 days gestation, the virus passes to the fetus. The fetus's immune system isn't developed enough to recognize the virus as an infection. By the time the immune system matures, the virus has become a natural part of the calf's system--a persistent, unrecognizable infection.

" Those calves will be infected for their lifetimes and only in very rare cases can you look at a calf and say 'That one is persistently infected,' " Brodersen said.

Until now, the only sure way to determine persistent BVD infection has been blood tests of calves 3 months and older. Brodersen found an accurate test that can be used on calves soon after birth. He tests a skin sample, rather than blood or serum.

" It's really just a new application of a test that has been around for awhile," he said. To test young calves, a veterinarian takes a small notch from the calf's ear and sends it to the diagnostic lab where it is processed like a routine biopsy sample. After the sample is cut into thin sections and put on a microscope slide, lab technicians perform a standard test to identify whether BVD is present in the tissue. The pathologist then examines slides for evidence of the BVD virus.

Blood tests often aren't accurate in young calves, who take in their mother's antibodies through the colostrum in her milk. These antibodies interfere with the BVD blood test.

" Using the skin test, we can identify infected calves at a younger age and remove them from the herd sooner, so there is less chance of them infecting other animals," Brodersen said.

Brodersen read about a similar skin test in a European scientific journal in 1996 and decided to try it at the lab. Each time a blood sample for a BVD test arrived, Brodersen contacted the veterinarian to get a skin sample from the same animal. He compared samples from more than 500 animals and found nearly 100 percent agreement between samples--proof that the test is very accurate.

To further confirm results, Brodersen collaborated with Iowa Sate University researchers to screen calves born in the 1999 calving season.

Of the more than 800 BVD tests the diagnostic lab runs monthly, the majority are from producers raising replacement heifers, particularly for dairies, Brodersen said.

" A few are clients who are screening pens of cattle in feedlots where they are seeing clinical signs of BVD and they are trying to identify a persistently infected animal within a pen," he said.

The BVD skin test is another step toward eradicating a disease that is a persistent problem for cattle producers. "BVD is classified scientifically under the genus pestivirus. It is very difficult to identify and eradicate. This test will make identification a little easier," Brodersen said.