Effects of Calcium Carbonate Particle Size, Phytase and Midnight Feeding on Performance, Egg and Bone Quality and Blood Parameters in Laying Hens.

BACKGROUND: To achieve maximum production in laying hens, calcium (Ca) and phosphorus (P) are two important minerals in the diet. Nutritional solutions such as adding coarser Ca particles in the afternoon or considering the light hours during the night to feed the birds might improve the eggshell quality and reduce Ca mobilization from the bone. OBJECTIVES: This experiment aimed to study the effect of calcium carbonate particle size (CCps), phytase (Pht) and midnight feeding (MF) on the performance, egg and bone quality and blood parameters in laying hens from 60 to 70 weeks of age. METHODS: A total of 720 Hy-line (W-36) laying hens were arranged in a factorial arrangement of 2 × 2 × 2 based on a completely randomized design with two types of CCps (100% fine and 75% coarse + 25% fine), two levels of Pht (0 and 300 FTU/kg) and two states of feeding (MF and without MF). The experimental period lasted 12 weeks from 60 to 70 weeks of age. RESULTS: During the trial, the significant impact of CCps on the feed conversion ratio (FCR) and breaking strength (BS) of the tibia was obtained (p < 0.05). FCR, eggshell percentage and the percentage of tibia ash, Ca and P were affected by Pht supplementation (p < 0.05). MF affected egg weight (EW), eggshell percentage and serum concentration of Ca, P and alkaline phosphatase (ALP) (p < 0.05). The interaction effects of CCps and Pht were significant for Ca level in serum (p < 0.05). CONCLUSIONS: In general, the use of Pht in the diets improved the FCR and quality of eggshell and tibia, and diets containing Pht and coarser CCps increased blood Ca levels. Despite the improvement of egg quality by MF, serum parameters showed a significant decrease.