Different Biological Responses of Pigs of Two Genetic Populations to PRRSV Challenge Suggests Underlying Genetic Variation in Susceptibility/Resistance to PRRSV

2004 University of Nebraska-Lincoln Extension Swine Report. The objective was to determine whether genetic variation in susceptibility to Porcine Respiratory and Reproductive Syndrome virus (PRRSV) exists. One hundred pigs from each of two distinctly different populations (NE Index Line, I, and Duroc-Hampshire cross pigs, DH) were challenged with PRRSV at 26 days old. A littermate to each challenged pig was included in the experiment without PRRSV challenge to serve as a control. Body weight and temperature were recorded and blood samples were drawn from all pigs on the day of challenge and 4, 7 and 14 days post-challenge. All pigs were sacrificed and a necropsy was performed on day 14. At necropsy, lungs were scored for evidence of interstitial pneumonia, lung tissue was collected for microscopic evaluation to determine incidence and severity of lesions, and aliquots of lung, lymph and spleen tissue were collected and stored. Interactions of line by challenge (PRRSV negative vs. PRRSV positive) were significant for several traits. I pigs challenged with PRRSV had greater weight gain, lower temperatures, replicated virus at lower rates in lungs, and lymph nodes, had fewer lesions, and lower ELISA values than DH pigs. Changes in temperature with time were similar for unchallenged I and DH pigs, and unchallenged DH pigs grew significantly faster than I pigs. Response of pigs of the two lines to PRRSV challenge differed indicating underlying genetic variation exists. Future research with tissues collected will determine which genes are expressed differently in pigs with resistant and susceptible responses to PRRSV.