Response to Ascaridia galli infection in growing chickens in relation to their body weight.

It was hypothesized that chickens with extremely varying body weights (BW) from an otherwise homogeneous host sample cope differently with Ascaridia galli (Schrank 1788) infection. Small and large birds, falling into either the lower or the upper 5% quantiles of BW distribution of a parent stock flock, were selected at an age of 4 weeks, housed separately and fed restrictively with the same amount of feed. At week 5, all the small and large birds (635 and 1,297 g/bird, respectively; P < 0.001) were inoculated with 1,000 A. galli eggs and euthanized 52 days post-infection. Small birds had higher daily weight gains (P = 0.004) but final BWs of larger birds were still higher (P < 0.001) at slaughter. Prevalence, intensity of infection as well as worm abundance were higher in small birds when compared with the large birds (P < 0.05), whereas plasma concentrations of A. galli-specific antibodies and worm length remained unaffected (P > 0.05). In conclusion, large birds resist A. galli infection more effectively than do small ones, possibly through different mechanisms acting on allocation of available nutrient and body reserves under the exposure of the infection.