Experimental injection of gilts with porcine reproductive and respiratory syndrome virus (PRRSV) during acclimatization

Objective: To evaluate the serological patterns of seroconversion in seronegative and seropositive replacement gilts after inoculation with the homologous strain of porcine reproductive and respiratory syndrome virus (PRRSV) as a method of acclimatization. Methods: In five herds, groups of replacement gilts that differed in PRRSV serological and exposure status were monitored by PRRS ELISA during the isolation-acclimatization period. Prior to arrival and isolation of the replacement animals, a potential source of herd-specific PRRSV was located. In each nursery, blood was collected 1 week after seroconversion from pigs that were presumed to be PRRSV-viremic. Serum from these animals was used as the inoculum for the replacement gilts. Five days post arrival (Day 0), gilts in Category A (seronegative gilts) and Category B (seropositive gilts) received an intramuscular injection of 2 mL of the serum preparation. Animals in Category C (seropositive gilts) were not exposed to PRRSV during acclimatization. Results: All Category A gilts seroconverted by 21 days post-inoculation, and ELISA sample:positive ratios decreased approximately 7 weeks after inoculation. Category B and C gilts had mixed responses after 21 days. Sample:positive ratios increased in the seropositive, inoculated gilts (Category B) and decreased in the seropositive, non-inoculated group (Category C). Implications: Inoculation of PRRSV-negative replacement gilts with serum from nursery pigs presumed to be PRRSV-viremic resulted in seroconversion of all 50 gilts tested.