Differences in Tibia Shape in Organically Reared Chicken Lines Measured by Means of Geometric Morphometrics

SIMPLE SUMMARY: Organic poultry production should use only genetic lines and animals resistant to disease and well adapted to live outdoor, according to principles, rules, and requirements of organic farming systems. When broiler’s walking performance is reduced animals are not suitable for outdoor rearing. There is a straightforward relationship between bone health and growth rate in broilers. Body and breast weight play an important role in leg disorders. During the last decades, genetic selection has led to high producing broilers over the time. Unfortunately, fast growth may negatively influence correct leg development, reducing walking performance, and raising welfare issues. Leg abnormalities could represent a criterion for the choice of genetic lines suitable for organic production. A method for their early detection was developed in this study by means of Geometric Morphometrics (GM) that represents a tool for bone shape analysis and its correlation with walking capability. A valuable information emerged from the present study in relation to broiler intrinsic adaptability to organic production. ABSTRACT: 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.