Background: It has been shown that zinc has an effect on physiological responses in animals and birds. On the other hand, dietary phytase in poultry results in increased availability of zinc. OBJECTIVES: This study was conducted to investigate the effects of zinc oxide (ZnO) and Escherichia coli-derived 6-phytase supplemented diets on the plasma metabolites and enzyme activities of broiler breeder hens from 60 to 72 weeks of age. METHODS: A total of 128 breeder hens were randomly assigned to eight dietary treatments, with four replicates of four hens each. Blood concentration of Zn, Ca, P, total protein, cholesterol, triglyceride (TG) and high density lipoprotein (HDL), and plasma activities of aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), and lactate dehydrogenase (LDH) were measured. RESULTS: Results showed that supplementary ZnO increased plasma Zn, Ca, P, HDL, and total protein (p<0.01) concentrations, as well as enzyme activities of LDH, ALT and AST (p<0.01). Also, a ZnO-supplemented diet resulted in a decrease in plasma cholesterol and TG (p<0.01) levels. Adding phytase to the diet increased plasma (P) and HDL contents (p<0.01). The interactive effect of phytase × ZnO × period on the plasma levels of Zn, P, total protein, HDL, total cholesterol, and the enzymatic activity of LDH, ALT and ALP was significant. CONCLUSIONS: It is concluded that supplementary ZnO and phytase may improve metabolism and enzymatic activity of aged broiler breeder hens.

Background: Old laying hens are more prone to dietary calcium (Ca) and phosphorus (P) deficiencies as  they absorb Ca and P less efficiently than younger hens. OBJECTIVES: In a 2×2 factorial design, the influence of diets with two levels of available phosphorus (AP) and phytase enzyme on the laying performance, egg quality and tibia bone characteristics of laying hens at their late 2nd production phase was studied. METHODS: The experiment used four treatments of 20 Hy-Line W36 hens of 140 weeks old. Treatments 1 and 2 received a 3.5 g kg-1 AP diet while Treatments 3 and 4 received a 2.5 g kg-1 AP diet for 12 weeks. Treatments 2 and 4 received 250 FTU kg-1 phytase in their diet. Laying performance, egg weight, shell weight and shell thickness were measured. On the last day of the experiment, all birds were weighed and blood samples were collected for serum Ca and P measurements. Ten birds from each treatment were sacrificed and both tibiae were excised, defatted, weighed and ashed for Ca and P contents, cortical thickness and bone breaking strength measurements. RESULTS: Hens fed with 2.5 g kg-1 AP diet without enzyme had the lowest body weight gain, serum P, tibia cortical thickness and tibia breaking strength among the treatments (p<0.05). Phytase enhanced body weight gain, egg shell thickness, serum P, tibia weight/body weight and tibia ash/body weight ratios, tibia cortical thickness and breaking strength, particularly in  birds receiving 2.5 g kg-1 AP diet (p<0.05). CONCLUSIONS: Phytase may improve bone quality and strength of hens  in the late 2nd laying period.