Optimization of drying specification and protein losses of poultry litter during drying process using response surface methodology

•Drying behavior of poultry litter was investigated.•Air temperature has the highest effect on crude protein and specific energy consumption.•Optimal specific energy consumption during the poultry litter drying was obtained.•Optimal crude protein and drying effectiveness during the drying of poultry litter was obtained.•Models were confirmed with experimental data to achieve the desired goals.