The mechanical properties of broiler chicken bones affected by different dietary zinc levels
The authors evaluated the effect of diet with different Zn levels on mechanical properties of bones in 120 broilers of Ross 308 hybrid, from 2 to 42 days of age, which were randomly divided into 2 groups, with 60 chickens each. The first group (Zn50) was fed commercial basal diet with no Zn additives (zinc content- 50 mg/kg feed). The second group (Zn100) was fed 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, grower and finisher. The clinical examination of the locomotory system showed the varus bone deformities of the intertarsal joint in 10% of broilers from group Zn50. Both tibiotarsal bones from 10 chickens from each group were dissected from fresh carcasses in weekly intervals on days 7, 14, 21, 28, 35 and 42 to evaluate the strength of tibiotarsus. The results obtained in the experiment showed the differences in biomechanical competence of broiler bones from group Zn50 as compared to Zn100. In broilers from group Zn100, there were significant higher values in the limit of elasticity (Re), bending strength (Rm) and fracture stress (Rl) (P<0.05 to P<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 as compared to Zn50 (95.27 ± 18.71, 100.2 ± 20.56, 80.93 ± 35.22, respectively). Moreover, there was a significant difference in the values of Rl between groups Zn50 and Zn100 on day 42 (P<0.05). In group Zn100, significantly increased values of bone cross-section area (Ar) were observed on days 14 and 35 and moment of inertia (I) on days 14, 21 and 35 (P<0.05). Results suggested that the determination of the weight bearing of tibial bone evaluated by the determination of mechanical properties of bones is a good indicator of the locomotory system disorders and the Zn content in feed has a direct statistical significant effect on bone strength in broiler chickens.
Key words: Zinc, broiler, bone, mechanical properties, three point bending test.