An examination of anatomic, physiologic, and metabolic factors associated with well-being of broilers differing in field gait score.

An experiment was conducted to evaluate potential differences for indicators of well-being in birds classified as having field gait score (FGS)2 and 3 and to evaluate potential causal factors affecting gait score. In 2 trials, birds with FGS2 and FGS3 were similar for most broiler traits (BW, feed conversion ratio) and fearfulness. Birds with FGS3, however, had improved breast conformation score in both studies and greater breast angle in the second trial compared with birds with FGS2. This improved breast conformation, along with differing ratios of length (hip to neck/hip to tail; P < 0.05), appears to be highly related to gait score. In other words, varying a bird's physical proportions necessitates that the bird's gait changes to maintain center of gravity during locomotion. In trial 2, behaviors were measured to determine if gait score affected behavior. Birds with FGS3 rested more and stood less than those with FGS2. Similar pathological analysis and heterophil:lymphocyte ratio suggest that gait score differences are not due to increased physiological stress or stress-associated pain. The lack of difference in heterophil:lymphocyte ratio, respiratory quotient, and pathology, combined with differing ratios of body proportions and anatomical length ratios, suggests that behavior and gait differences between birds with differing FGS occur with similar levels of well-being.