Exogenous α-amylase supplementation reduces the variability of ileal digestible energy in broiler chickens fed complete diets with maize batches of variable protein solubility

•α-amylase reduced the FCR of chickens from 1 to 28 d from 1.407 to 1.426.•α-amylase increased ileal digestible energy (IDE) from 12.21 to 12.50 MJ/kg dry matter.•There was a negative correlation between IDE of maize and the response to α-amylase.•α-amylase reduced the variability of energy digestibility from a CV of 5.2 % to 0.7 %.