Calves born with deformed limbs are bound to make producers worry about genetic problems. But they can indicate a more difficult problem: an animal in the herd is persistently infected with Bovine Viral Diarrhea (BVD).

BVD is a serious cattle disease, causing estimated losses of up to $150 million annually nationwide. Symptoms range from mild to severe diarrhea. BVD 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, said Bruce Brodersen, veterinary pathologist at the University of Nebraska's Veterinary Diagnostic Laboratory.

"You can lose up to 10 percent of the calves born in a herd from severe diarrhea and concurrent infections," he said, if a persistently infected animal infects others.

BVD virus spreads from animal to animal in a herd. When the virus infects a pregnant cow at between 80 and 150 days gestation, it 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,'" the Institute of Agriculture and Natural Resources scientist said.

Breeding stock producers are beginning to test for BVD fairly routinely; others tend to test only if a problem appears. 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 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 Veterinary 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, Brodersen runs a standard test to identify whether BVD is present in the tissue.

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 is collaborating with Iowa State University researchers, screening calves born in the 1999 calving season.

Interest in the test is strong, Brodersen said. After he presented information about the test at a national professional meeting, calls began coming in from across the country. Posting test results on the American Association of Veterinary Laboratory Diagnostics computer listserv and in the Nebraska Veterinary and Biomedical Sciences Newsletter on the World Wide Web also has generated interest.

"BVD is what is known scientifically as a 'pestivirus'. It is very difficult to identify and eradicate. This test will make identification a little easier," Brodersen said.

- Monica Manton Norby

IANR Veterinary Pathologist Bruce Brodersen prepares a skin tissue sample from a calf to test for Bovine Viral Diarrhea, a serious cattle disease.

A closeup of tissue sample processing for viewing under a microscope. The skin sample test can detect BVD in calves hours after birth, months earlier than blood tests.

Veterinary Pathologist Bruce Brodersen takes a small notch from a calf's ear for testing at NU's Veterinary Diagnostic Laboratory. His research shows that a skin sample test accurately identifies young calves that are infected with Bovine Viral Diarrhea.