Effect of copper supplementation on performance, eggshell quality and heterophil: Lymphocyte ratio in aged laying hens housed at different stocking densities

This study was conducted to determine the effects of additional dietary copper on performance, eggshell quality and heterophil:lymphocyte ratio in aged laying hens housed at different stocking densities. For this purpose, 216 Nick Chick laying hens of 106 weeks of age, were housed at three different stocking densities i.e. 500, 417 and 357 cm2/hen, respectively and copper (0, 150 and 300 mg/kg) was added in the basal diet for a period of 10 weeks using a 3x3 factorial arrangement. The effect of the treatments on body weight gain, feed intake, damaged eggs, specific gravity and eggshell breaking strength were not significant (P > 0.05). However, eggshell thickness was improved (P < 0.05) with increasing stocking density in the aged laying hens. Additionally, added copper had a significant effect on egg production (P < 0.05), egg weight (P < 0.01), egg mass (P < 0.01), feed conversion ratio (P < 0.01) and eggshell weight (P < 0.01). While added copper had a significant adverse effect on eggshell weight, the addition of copper had a significant positive effect on performance parameters. Highest stocking density resulted in increased (P < 0.05) heterophil:lymphocyte ratio. Addition of 150 and 300 mg/kg copper in the diet of the birds kept at 500 cm2/hen stocking density reduced heterophil:lymphocyte ratio as compared to other groups. It may be concluded that supplementation copper in the diet of aged laying hens decreased stress under normal stocking density, while stress was increased to the birds under high stocking density.