Document Type : Research Paper
Authors
Abstract
The experiment was designed to study the changes in production performance and egg quality of old laying hens after injection of different doses of growth hormone (GH) and testosterone (Ts). A total of 160 old laying hens (HyLine W-36) at 73 wks of age were randomly assigned to four treatments with four replicates and 10 birds in each replicate in a completely randomized design. Treatment groups were: treatment 1: injection of 100 µl distilled water (control group), treatment 2: injection of 500 µg Ts/kg live-weight+50 µg GH/kg live-weight, treatment 3: injection of 500 µg Ts/kg live-weight+100 µg GH/kg live-weight and treatment 4: injection of 500 µg Ts/kg live-weight+150 µg GH/kg live-weight. During second and third weeks after the hormone injection production performance and egg quality parameters were measured. Ovulation rate (egg production percent), egg mass and feed intake of treatment three significantly increased compared to control group (p<0.05). Feed conversion ratio (FCR) was significantly higher in treatment four compared to other treatments (p<0.05). Treatment 3 caused higher egg weight, albumen height, eggshell weight, eggshell density and eggshell weight per surface area (ESWSA) compared to control group (p<0.05). Yolk height in treatment 2 was significantly lower than other treatments (p<0.05). Shell breaking strength of control group was significantly higher than all injected groups. In conclusion, our results showed the positive effects of GH and Ts administration on old laying hens’ performance and egg quality parameters
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