Effects of lineage and sex on geometrical and biomechanical properties of broiler chickens tibias/Efeito de linhagem e sexo nas caracteristicas geometricas e biomecanicas de tibias de frangos de corte

The intensive rearing of broilers, combined with nutrition and genetic improvement focused on weight gain has resulted in increasing rates of leg problems. Among the variables that may contribute to the occurrence of these problems are sex and lineage. In this context, the study evaluated the geometric and mechanical properties of the tibiae of broilers, male and female, from three commercial lines in the final growth stage, between 21 and 42 days. The geometric characteristics reflect the adaptive response of bone, with a direct relationship between their dimensions and the live weight of birds. As for the mechanical properties obtained from bending tests, it is observed that the evaluation of bone strength can lead to different conclusions depending on the mechanical parameter considered. Heavier birds, with larger bones, support more load in bending. However, when intrinsic strength parameters of the material are considered, such as bending strength, it is observed that the heavier line does not show significantly different values from the others. The same occurred among males (heavier) and females. Thus, heavier birds may be more susceptible to structural leg problems, as their tibias are as strong as those from lighter birds. Key words: sexual dimorphism, mechanical tests, leg problems, bone strength. A criacao intensiva de frangos de corte, aliada a nutricao e ao melhoramento genetico com foco no ganho de peso, tem resultado em indices crescentes da incidencia de problemas de pernas. Dentre as variaveis que podem contribuir para a ocorrencia destes problemas, estao a linhagem e o sexo. Neste contexto, avaliaram-se propriedades geometricas e mecanicas de tibias de frangos de corte, machos e femeas, de tres linhagens comerciais no periodo final de crescimento, entre 21 e 42 dias. As caracteristicas geometricas refletem a resposta adaptativa dos ossos, com relacao direta entre suas dimensoes e o peso vivo das aves. Quanto as caracteristicas mecanicas obtidas de ensaios de flexao, observa-se o que o julgamento da robustez ossea pode levar a conclusoes diferentes dependendo da variavel mecanica considerada. Aves mais pesadas, com ossos maiores, suportam forcas maiores na flexao. Entretanto, quando variaveis de resistencia intrinsecas do material sao consideradas, como resistencia a flexao, observa-se que a linhagem mais pesada nao apresenta resistencia a flexao significativamente diferente das demais. O mesmo ocorre entre machos (mais pesados) e femeas. L