Dietary combination of chelated zinc and threonine and effects on egg production, egg quality and nutrient balance of Brown laying hens from 20 to 49 weeks of age

•Zinc and Threonine interact on egg production of laying hens.•Levels above 40 mg/kg of chelated Zn may affect nutrient and energy intake.•Corn and soybean meal diet met the daily demands of Zn from 20 to 48 weeks of age.•Current laying hens require higher consumption of Thr for egg production.