The influence of dietary zinc content on mechanical properties of chicken tibiotarsal bone

The authors evaluated the effect of diets with different Zn levels on mechanical properties of bones in 60 Ross 308 hybrid broilers, from 2 to 35 days of age, which were randomly divided in 2 groups, with 30 chickens each. The first group (Zn50) was fed a commercial basal diet with no Zn additives (zinc content - 50 mg/kg feed). The second group (Zn100) was fed the basal diet + 50 mg of Zn/kg feed. In this group the dietary Zn level was increased by adding 62.23 mg of zinc oxide (ZnO)/kg feed to starter and grower feeds. In group Zn100 compared to Zn50 the values of blood zinc level were significantly higher on days 7 and 35 (p is less than 0.01 and p is less than 0.05). Significant differences in bone zinc content were not detected. On days 7, 21, and 35 the selected mechanical properties of the tibiotarsus were evaluated. The results obtained in the experiment showed differences in biomechanical competence of broiler bones from group Zn50 compared to Zn100. In broilers from group Zn100, there were significantly higher values in the limit of elasticity (Re), bending strength (Rm) and fracture stress (Rl) (p is less than 0.05 to p is less than 0.01) of chicken bones on day 35. The mean levels (117.80 +/- 19.66, 126.70 +/- 32.56, 114.10 +/- 19.92, respectively) were determined in broiler bones from group Zn100 compared to Zn50 (95.27 +/- 18.71, 100.2 +/- 20.56, 80.93 +/- 35.22, respectively). In group Zn100 were observed significantly increased values of the bone crosssection area (Ar) on day 35 and moment of inertia (I) on days 21 and 35 (p is less than 0.05). The clinical examination of the locomotory system showed bone deformities of the intertarsal joint in 10% of broilers from group Zn50. Present results suggest that the determination of the weight bearing of the tibial bone evaluated by assessing of mechanical properties of bones is an indicator of the locomotory system disorders and the Zn content in feed has a direct and statistically significant effect on bone strength in broiler chickens.