Proteolytic enzyme variants that exhibit improved thermal stability relative to the wild type protease Bacillus licheniformis PWD-1 protease kerA are provided. The protease variants are derived by the mutation of at least one amino acid residue of the mature Bacillus licheniformis PWD-1 protease kerA. The variant proteases are useful as animal feed additives to improve the digestibility and/or the nutritional value of the animal feed.