A voluntary health certification plan for producers who want to buy and sell PRRS (Porcine Reproductive and Respiratory Syndrome)-negative breeding stock is in the early stages of development by the South Dakota Animal Industry Board.

Extension Veterinarian Bill Epperson describes the motive for the program. "Our producers on the planning committee for this program were very concerned because they would be purchasing animals that would be claimed to be PRRS-negative from herds that were vaccinating for PRRS."

He says the uncertainty of PRRS status of a herd led the board to develop a herd certification program in hopes of controlling and eliminating the disease.

South Dakota producers can certify either a premise or an entire operation. A sampling scheme and certification plan can be built with the herd veterinarian.

Each participating herd owner must sign a certification statement, agreeing to meet sampling and identification requirements of initial certification and monitoring for maintenance of certification (see Table 1).

Epperson stresses the program is designed to certify production systems, and not individual animals, that are PRRS-negative. The program is based on probability testing. Relatively small samples are taken in various stages of production. A one-year grace period is required before producers are certified.

Participation will be limited to those who are interested in being PRRS-negative and who are not vaccinating for the disease, says Epperson.

Enrolled herds will be studied in depth during their one-year phase of initial certification to provide some basis for the effectiveness of the program, he explains.

The study will look in depth at a specific area of concern: the 0.4 level of the ELISA serology test that is used as the cutoff of whether a hog is PRRS positive or negative.

"I think what people are learning experimentally is that in some cases levels below 0.4 may actually also be indicating that the animal is positive for PRRS, " explains David Benfield, South Dakota State University. He adds there is enough uncertainty over the validity of the 0.4 level to warrant looking at a different, lower cutoff value.

"I think it might be beneficial to the use of the ELISA test, especially as we get into test and removal or control programs for PRRS," states Benfield.

For more information, contact Epperson, (605) 688-6649 or Sam Holland, state veterinarian, (605) 773-3321.