Effect of dietary protein levels, sex and age on tibiae charateristics in two strains of broiler chickens

Abstract

Cobb 500 and Hubbard Classic broiler chicks were reared on the floor during seven weeks of fattening. Chicks, of each strain, were divided in two groups (160 chicks in group) and feed with two isocaloric diets differed in protein levels. The contents of crude protein in the diets 1, were 23 % (1-2 weeks of age), 22 % (3. week), 21 % (4 - 6 weeks), 18 % (7. week) and in the diets 2 were 22 % (1 - 2 weeks), 21 % (3. week), 20 % (4 - 6 weeks) and 17 % (7. week of age). At days 35, 42 and 49, 10 male and 10 female chicks were sacrificed from both strain and both group. The right tibiae were removed and prepared for analysis. Bone breaking force were determined by three-point-bending test at the midlength. Geometrical properties were obtained by measuring of outside and inside antero-posterior and lateromedial diameters, at the middiaphyseal transverse section of each tibia. These data were used to calculated of bones cross sectional cortical area and cross sectional medullar area. The obtained results showed that cross sectional cortical area and cross sectional medullar area increased with age and were influenced by strain and sex but not by dietary protein levels. Hubbard Classic chicks had higher cortical and lower medullar area than Cobb 500 chicks. The breaking force and ratio cortical/medullar area were significantly (p< 0.05) greater in male than in female chicks of each strain. The male chicks of both strain, fed the diets 2, during six weeks of fattening, had the largest tibiae breaking force (47.0-50.0 kg) but the differences were not significant. Geometrical and mechanical characteristics of broilers tibiae were notsignificantly influenced by dietary protein levels.