PALMERSTON NORTH, April 26th (Biermann) – Dr. Fraser I. Hill from Gribbles Veterinary in Palmerston North, New Zealand, and his colleagues noticed that in recent years, there has been a rise of interest in the diagnosis of BVDV in New  Zealand cattle. Thus, they began searching for an alternative, cost-effective way to identify the virus. In this study, they tried using real-time reverse transcriptase polymerase chain reaction (RT-PCR) technology and dairy cow production data to see whether persistently infected (PI) animals in milking herds could be successfully identified.

The authors collected milk samples from the vats of dairy herds and tested them for the presence of BVDV via RT-PCR. They found four herds that contained PI animals. From these herds, individual serum probes from each cow were collected and tested by both RT-PCR and antigen capture enzyme-linked immunosorbent assays (ACE) to identify PI animals. A total of five positive cows were found, with a distribution of 1/223, 1/130, 2/800 and 1/275 PI’s respectively in the four herds. The researchers then selected a maximum pool size of 400 cows contributing to the bulk tank milk. The PI animals were removed from the herds and the bulk milk samples were again tested by RT-PCR to determine the presence of BVDV. The results were negative, as expected.

“All PI animals identified by this method were found in the lowest producing 10-20% of herd”, Dr. Hill and his team note. They thus conclude that targeted testing of dairy herds by PCR in conjunction with animal production information has markedly reduced the cost of diagnostic testing for BVDV in New Zealand dairy herds. Lastly, the researchers performed a follow-up survey on 81 BVDV-positive herds (15% of those tested), which indicated that the stratification approach has successfully identified milking Pis over 90% of the time and reduced the number of individual tests to 12% of the milking herd.

References

• Vet. Microbiol. 142(1-2):87-89