15. Comparison of the Effect of a Standard Inclusion Level of Inorganic Zinc to Organic Form at Lowered Level on Bone Development in Growing Male Ross Broiler Chickens

The purpose of this study was to compare the effect of a standard inclusion level of inorganic zinc to organic form at lowered level on the bone development in growing male Ross 308 chickens, assessed on the basis of mechanical, geometric, and histomorphometric parameters of limb bone, and bone zinc content, as well as hormones of somatotropic axis. A total of 80 one-day-old male Ross broiler chickens were randomly allocated to 2 groups of 40 chickens each. The control group was fed with a corn-soybean meal basal diet providing the recommended zinc amount (100 mg×kg^-1) from zinc oxide, and the experimental group was supplemented with glycinate chelate providing 25% of the total requirement of the microelement recommended for Ross 308 broiler chicks. The mechanical and histomorphometric parameters and geometry of tibia were determined as well as the serum concentration of growth hormone, IGF-1, osteocalcin and leptin. The serum concentration of Zn, Cu, Ca, Mg, Fe, P and zinc bone content were determined. The results showed that birds fed with the diet supplemented with organic zinc in the amount of 25% of the recommended amount did not exhibit weight and general growth disorders and had an unchanged concentration of growth hormone, leptin, and IGF-1. The serum concentration of Zn, Cu, Ca, Mg, Fe, P did not differ between groups. The contents of zinc detected in bones in the controls and the group supplemented with the organic source did not differ as well. Although tibial mechanics and geometry remained unchanged, histomorphometry revealed a disproportionately large osteoporotic bone. The changes in tibial trabecular bone as a result of the diet supplemented with glycinate chelate only in 25% of the total requirement of the microelement recommended for Ross 308 broiler chicks seems to be insufficient for tibia development.