Effect of Dietary Supplementation with 1, 25- Dihydroxy Cholecalciferol (Calcitriol) on Performance, Tibia Mineral Alterations and Ileal Nutrient Digestibility in Laying Hens Fed Diets with Deficient Calcium-Phosphorus Level

To investigate the effect of dietary calcitriol supplementation on performance, bone mineral turnover and ileal nutrient digestibility of laying hens fed diets deficient in calciumphosphorus (Ca-P) level, 100 Hy-Line W-36 laying hens (56 wk-aged) were randomly distributed between 5 replicates of 4 dietary treatments. Experimental Diets included two dietary Ca-P levels (sufficient as recommended by Hy-line W-36 guideline versus 20% deficient) and two vitamin D sources (D3 or calcitriol), which fed during a 77 d trial period including 7 d for adaptation and 70 d as main recording period. The highest egg production allotted to the birds fed on Ca-P-sufficient diets supplemented with calcitriol. There was a significant (P<0.05) interaction between dietary Ca-P level and vitamin source in the light of egg production percentage so that, decrease in dietary Ca-P level was associated with higher decrease in egg production in calcitriol-supplemented diets than with D3-supplemnetd ones. Regardless of dietary Ca-P level, the best feed conversion ratios assigned to the calcitriolsupplemented birds. Dietary supplementation with calcitriol increased tibial Ca (P<0.01) and P (P<0.05) contents and the least concentration (P<0.05) of tibial Ca was observed in hens fed on Ca-P-deficient diets. Dietary treatments had significant (P<0.05) impacts on ileal digestibility coefficients of dry matter, Ca and ash; however, P and crude protein digestibilities weren't influenced by dietary Ca-P level or vitamin source. The present findings indicate that calcitriol supplementation of laying diets could improve overall performance and bone mineralization in layers.