Differences in tibia shape in organically reared chicken lines measured by means of geometric morphometrics

In the present study, the conformation of the tibia of seven genetic lines of broilers was analyzed by Geometric Morphometrics and correlated to carcass weight and walking ability. The used chicken genetic lines were classified as fast, medium, or slow growing and ranked for their walking ability. Six chicken types were reared in an organic farm and slaughtered at 81 days of age while one slow-growing and highly walking line (Naked Neck) was reared in a commercial farm and used as external reference for moving activity and growth speed. A mixed landmarks and semi-landmarks model was applied to the study of tibia shape. Results of this study showed that: (i) body weight gain was positively correlated to the curvature of the antero-posterior axis of the tibia; (ii) the shape of the tibia and the active walking behavior were significantly correlated; (iii) walking and not-walking genetic lines could be discriminated in relation to the overall shape of the tibia; (iv) a prevalence of static behavior was correlated to a more pronounced curvature of the antero-posterior axis of the tibia. Results of this study revealed that the walking genetic types have a more functional and natural tibia conformation. This easy morphologic method for evaluating tibia shape could help to characterize the adaptability of genotypes to organic and outdoor rearing.