Influence of Growth Selection in Turkeys on Resistance to Pasteurella multocida

: Four lines of turkeys, a randombred control (RBC2) started in 1966 and three sire lines (F, A, and B), were challenged with a field isolate of Pasteurella multocida (capsular serogroup A, somatic serotype 3, 4) at 6 wk of age. Line F, a subline of the RBC2 line, was selected for 28 generations for increased 16-wk BW and Lines A and B were primary breeding sire lines from two commercial breeders. Each bird was inoculated subcutaneously in the back of the neck with 1.2 x 10(7) washed bacteria. Mortality following challenge with P. multocida was higher in the sire lines (54 to 65%) than in the RBC2 line (26%). There was no significant difference in mortality among sire lines following challenge. These results suggest that the increased susceptibility to P. multocida in the F line in comparison to its control may be due to genetic changes resulting from selection for increased BW in this line.