Comparison of mean and standard deviations of (a) heterophil/lymphocyte ratio (H/L ratio), (b) plasma corticosterone concentration and (c) blood glucose concentration between small and large 4 weeks old broiler breeder females. Permutations tests, small n = 21, large n = 21. Asterisks indicate significant differences (* P ≤ 0.05).

Comparison of mean (SD) organ masses and mean (SD) intestine lengths relative to lean body mass between small and large 4 weeks old broiler breeder females. Permutations tests, small n = 36, large n = 33. Asterisks indicate significant differences (* P ≤ 0.05, ** P ≤ 0.01, *** P ≤ 0.001).

Comparison of mean (SD) absolute muscle mass and mean (SD) muscle mass relative to lean body mass between small and large 4 weeks old broiler breeder females. Permutations tests, small n = 15, large n = 12. Asterisks indicate significant differences (* P ≤ 0.05, ** P ≤ 0.01, *** P ≤ 0.001).

The table shows comparisons of body size, organ masses relative to lean body mass, fat depots and crop and stomach content between small and large 4 weeks old broiler breeder females. Permutations tests, small n = 36, large n = 33, values are shown as mean (SD). Asterisks indicate significant differences within a row.

The original hypothesis of poorer welfare of small birds is not supported in the present study. It seems likely that small and large broiler breeders experienced the same amount of feed restriction (no difference in absolute crop fill), that small birds had a relatively larger gastrointestinal tract, pancreas and liver (a more efficient digestive system) and that small birds did not show sign of higher stress levels, which might indicate that small broiler breeders were more successful in coping with feed restriction and maybe that they are better habituated to the industry environment.