Scott A. Dee. DVM. MS: Robert B. Morrison, DVM, PhD; HanSoo Joo, DVM, PhD
We attempted to eradicate porcine reproductive and respiratory syndrome (PRRS) virus using early weaning and two-site production. We chose this method over depopulation or test-and removal procedures because the infection was highly prevalent in the breeding herd (63%), the breeding herd was very valuable (a seedstock operation), and because another farm was concurrently available. Modified medicated early weaning (at 14 days) was also used to try to eradicate other chronic respiratory diseases detected in the herd.
Samples taken from pigs raised on-site were positive by indirect-fluorescent antibody (IFA) assay. Animals tested at the o$site facility (90 head) were negative by IFA for 4 months, but then infection occurred. PRRS virus was isolated from one pig in the nursery and all pigs tested were seropositive to PRRS virus. The source of the virus was thought to be a carrier pig.
No evidence of pneumonia was detected at slaughter, and this observation in conjunction with a lack of clinical signs indicated that in this high health herd, PRRS infection was subclinical. five to 6 months after infection, IFA titers in 5- to 6-month-old pigs decreased from 1024 to undetectable (0-16) over 5 months. Nursery pigs were seronegative at weaning and seroconverted to PRRS virus at 8-10 weeks of age. Because the nursery appeared to be the area where virus was recirculating, we attempted to eradicate PRRS by depopulating the nursery. After normal pig flow resumed, all pigs tested have remained negative for PRRS antibody.