Effects of boron and copper dietary supplementation in laying hens on egg shell quality, plasma and tibia mineral concentrations and bone biomechanical properties

This study was conducted to determine the effects of supplementation of different boron and copper doses on eggshell quality, bone biomechanical properties, mineral concentrations in bone and plasma in laying hens. A total of 320 Lohmann laying hens, 26 weeks old, were randomly allotted in 16 equal groups according to the combined doses of boron (0, 60, 120 and 240 mg/kg) and copper (0, 75, 150 and 300 mg/kg) added to the basal diets for 16 weeks. Eggshell quality parameters (frequency of damaged eggs, specific gravity, eggshell breaking strength, eggshell thickness, egg shell weight), bone biomechanical properties (cortex thickness, cortex cross section area, shear force, shear stress, fracture energy) and bone (tibia) and plasma mineral (B, Cu, Zn, Ca, P and Mg) concentrations were determined at the end of the experimental period. Added boron exhibited adverse effects on eggshell quality parameters (significant decrease in eggshell thickness) but has significantly promoted trace element (B, Cu and Zn) distribution and accumulation in bones without severely affecting bone Ca, P and Mg contents, and has significantly increased bone resistance (increases in cortex thickness, shear force, shear stress and fracture energy). Cu supplementation has not directly and significantly modified bone properties or B, Cu and Zn distribution and accumulation, although at 150 and 300 mg/kg Cu doses, the B fixation was exacerbated whereas the divalent ion accumulation was slightly depressed. In addition, the eggshell solidity was significantly improved (increases in specific gravity, eggshell breaking strength, eggshell thickness and eggshell weight). These results indicate that B and Cu supplementation interfere with trace element metabolism leading to improvement of egg shell quality (Cu) or to bone resistance (B).