Comparative effects of organic, inorganic and hydroxy zinc sources on performance of aged laying hen

The current experiment was conducted to investigate the effects of zinc different sources, inorganic, organic and hydroxy, in the diet on performance and egg quality of aged laying hen. A total of 288 hy-line W-36 hens, from 65 to 73 weeks of age were used. The study carried out in a completely randomly design, with 6 treatments, 4 replicates, each contains 12 hens. The treatments consisted of: 1- zero level mg/kg of zinc supplementation (control) 2- control+ 70 mg/kg of zinc as zinc sulphate (inorganic source) 3- control+ 70 mg/kg of zinc as zinc-methionine complex (organic source), and treatments 4, 5 and 6 consisted of control diets supplemented with 50, 70 or 90 mg/kg of zinc as zinc chloride hydroxide, respectively. All experimental treatments decreased feed conversion ratio and increased eggshell strength (during experiment), egg weight (8th week), yolk index and haugh unit (6th and 8th weeks) compared to the control group. The zinc organic and hydroxy sources increased significantly (P<0.05) percentage of eggshell, levels of blood and tibia zinc, blood albumin and antibody titer against Newcastle disease compared to control group. The zinc sulphate only increased blood zinc level. There were no differences in feed intake, production, specific gravity, eggshell thickness and shape index of egg due to supplementation with zinc. The results of this study suggest that 50 mg/kg zinc hydroxyl source can be a replacement for 70 mg/kg zinc sulphate or complex of zinc-methionine in aged laying hen diet.