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Biological responses to porcine respiratory and reproductive syndrome virus in pigs of two genetic populations^1,2

Department of Animal Science, University of Nebraska, Lincoln 68583-0908

⁵ Correspondence: A218 Animal Sciences (phone: 402-472-6404; fax: 402-472-6362; e-mail:rjohnson5{at}unl.edu).

One hundred pigs from the NE Index Line (NEI) and 100 Hampshire-Duroc cross pigs (HD) were inoculated intranasally with porcine respiratory and reproductive syndrome virus (PRRSV 97-7895 strain) at 26 d of age to determine whether genetic variation in response to PRRSV exists. An uninfected littermate to each infected pig served as a control. Pigs were from 163 dams and 83 sires. Body weight and rectal temperature were recorded, and blood samples were drawn from each pig on d 0 before inoculation and on d 4, 7, and 14 after inoculation. Pigs were sacrificed on d 14. Lung and bronchial lymph nodes were collected, placed in optimal cutting temperature compound, and frozen at –80°C. The presence of PRRSV in serum and in lung tissue and bronchial lymph nodes was determined by isolation in cell culture. The presence of antibodies in serum collected on d 14 was determined by a commercial ELISA test. Lung tissue was examined microscopically and scored for incidence and severity of lesions (score of 1 to 3; 1 = no or few lesions, and 3 = severe interstitial pneumonia). Data were analyzed with a mixed model that included random sire and dam effects. The interaction of line x treatment was significant (P < 0.001) for weight change and rectal temperature. Un-infected HD pigs gained 0.67 kg more from d 0 to 14 and averaged 0.32°C higher rectal temperature than uninfected NEI pigs (P < 0.001), whereas infected NEI pigs gained 0.34 kg more and had –0.54°C lower temperature than infected HD pigs (P < 0.001). Viremic titer (cell culture infectious dose 50%/mL) was greater (P < 0.05) in HD than NEI at d 4 (10^4.52 vs. 10^4.22), 7 (10^4.47 vs. 10^3.99), and 14 (10^3.49 vs. 10^3.23). Viral titer loads in lung (P = 0.11) and bronchial lymph nodes tended (P = 0.07) to be greater in HD than NEI pigs. Antibody signal-to-positive (S/P) ELISA ratios in infected pigs ranged from 0.18 to 3.38, and 88% had levels 0.40, which is the positive threshold for this ELISA. The S/P range in uninfected pigs was 0 to 1.11, and 99% had levels 0.40. Mean S/P ratio for infected pigs was 0.23 units higher in HD than in NEI (P < 0.001). The HD pigs had a greater incidence of interstitial pneumonia and 0.65 higher mean lesion scores than NEI pigs (P < 0.001). In summary, responses of pigs of the two lines to infection with PRRSV differed, indicating that underlying genetic variation existed.

Key Words: Biological Indicators • Genetic Variation • Virus

This article has been cited by other articles:

				D. B. Petry, J. Lunney, P. Boyd, D. Kuhar, E. Blankenship, and R. K. Johnson Differential immunity in pigs with high and low responses to porcine reproductive and respiratory syndrome virus infection J Anim Sci, September 1, 2007; 85(9): 2075 - 2092. [Abstract] [Full Text] [PDF]