Is Dietary Zinc Requirement of Broiler Breeder Hens at the Late Stage of Production Cycle Influenced by Phytase Supplementation?

This experiment was conducted to determine whether 6-phytase has a positive effect on zinc requirements, production performance, and zinc content of tissues in broiler breeders at the end of their production cycle. One hundred and twenty-eight obese Cobb500 broiler breeder hens (>v4.9 kg) were weighed at 58 weeks of age and assigned to various treatment groups. To deplete the zinc reserves in hens, they were given a zincdeficient diet (9.5 mg kg(-1) of zinc) and drank water with 35 mu g L-1 zinc for two weeks. Then, hens were randomly allocated to 8 dietary treatments in a factorial arrangement of two levels of phytase (0, 300 FTU kg(-1)) and four levels of dietary zinc (30, 60, 90, 120 mg kg(-1)) with four replicates of 4 hens in each. Bodyweight, egg production, egg weight, and egg quality were measured during the five-week experimental period. Added zinc significantly increased yolk weight and zinc content of yolk (P< 0.05) and plasma (P< 0.0001). Egg weight was significantly increased by adding phytase (P< 0.05). As the results of this experiment show, adding exogenous phytase can decrease the zinc requirement of broiler breeder hens by releasing 16.9% of the zinc bound to phytate.