Effect of different vitamin D sources and calcium levels in the diet of layers in the second laying cycle

This study evaluated the effects of different sources of vitamin D and calcium levels on performance, egg quality and bone strength of hens in the second production cycle. A total of 384 Hy-Line W36 birds with 80 weeks of age were used, alloted into 3 x 4 factorial design (sources of vitamin D: cholecalciferol; 25(OH)D3 and 1.25(OH)2D3 x calcium levels: 2.85, 3.65; 4.45 and 5.25%) with four replicates and eight birds each. The performance was evaluated for three cycles of 28 days each, egg quality was evaluated in the last four days of each cycle and bone strength on the last day of the experimental period. There was no interaction (p > 0.05) between the different sources of vitamin D and calcium levels in all parameters evaluated. There was a quadratic effect (p < 0.05) of calcium levels in egg production and feed conversion (kg/kg and kg/dz), with better results at levels of 4.12%, 4.09% and 4.14%, respectively. Calcium levels had no effect (p > 0.05) in the egg weight and Haugh unit, but there was a linear increase (p < 0.05) in the percentage and eggshell thickness, in specific gravity and bone strength. The different sources of vitamin D influenced (p < 0.05) the egg production rate, feed conversion, egg weight and Haugh unit. Thus, the results of this study suggest that the recommended calcium level for laying on second cycle is between 4.09% and 4.14% and that the metabolites cholecalciferol and 25(OH)D3 improved the performance and egg quality. Regarding bone strength was improved as the calcium levels were increased in diets