Influence of body weight restriction in a body-weight-selected line of turkeys on response to challenge with Pasteurella multocida

Previous research has shown that a line (F) of turkeys selected long-term for increased l6-wk BW vas more susceptible to challenge with washed Pasteurella multocida (PM) than a randombred control line (RBC2), the base population of the F line. Published research indicated that the mortality of the F line following challenge with PM was similar to that of two commercial sire lines. The purpose of the present study was to determine the influence of reducing BW of the F line to that of the RBC2 line by nutrient restriction on resistance to PM. Four challenge trials were conducted over a 2-yr period. The BW of a group of F line birds was restricted to that of the RBC2 line by limiting access to feed from 1 to 6 wk of age. The F line restricted birds and full-fed RBC2 and F line birds were challenged with a field isolate of washed PM (1.2 x 10(7) organisms/bird of capsular serogroup A and somatic serotype 3, 4) at 6 wk of age. Birds were checked twice daily for 14 d. Resistance to PM was measured by days to death of those that died and percentage mortality. The BW of the restricted group of the F line did not differ from full-fed RBC2 birds for males or females. In males, the restricted F line birds had similar mortality (48.0%) to the full-fed RBC2 line birds (44.3%), and the mortalities in both groups were significantly lower than that observed for the full-fed F line birds (81.3%) following challenge with PM. The mortality following challenge in females did not differ significantly among groups, even though mortality of the full-fed F line birds (64.1%) and restricted F line birds (63.3%) was more than 9% higher than that (54.2%) observed for the full-fed RBC2 line birds. Days to death was not a sensitive indicator of resistance to PM, as no differences among the three groups of birds were observed for either sex.