Differences in susceptibility to Haemophilus parasuis infection in pigs.

In animal breeding programs, deoxyribonucleic acid (DNA) markers can be used to identify sires that are less susceptible to disease. These DNA markers are typically discovered in populations that display differences in susceptibility. To find those differences, it was hypothesized that sires influence their offspring responses to infection with H. parasuis. To identify differences in susceptibility, colostrum-deprived pigs derived from 6 sires were inoculated with a virulent strain of H. parasuis serovar 5. Pigs were infected at 21-d of age and euthanized 1, 2, or 3 days post-infection. Rectal temperatures, bacterial detection, clinical signs, and lesions were measured by comparing disease susceptibility in the offspring from each sire. The effect of the sire on the severity of disease in the offspring was statistically analyzed using to a 2-way ANOVA with sire and test day as fixed effects. Significant differences among sires were found for lesions, rectal temperatures from days 0-1 and 0-2 (P < 0.05) and marginal effects for clinical signs (P = 0.08). On average, the offspring of sire H94 was the most susceptible to challenge. Responses to infection were categorized to determine the clinical responses and analyzed by Chi square. Overall, 10% of all pigs infected were fully resistant to H. parasuis infection. Boar H94 didn't produce any fully resistant offspring. Differences in susceptibility to H. parasuis were observed, and the results support the hypothesis that sires influence their offspring's response to infection. Tissues from this population could be used to identify DNA markers for genetic selection of sires that produce offspring more resistant to H. parasuis infection.