Compositions for preventing or decreasing cryptosporidiosis in animals are disclosed herein. The compositions include sources of hydrogen peroxide and are fed to animals. The animals may be neonatal calves and the cryptosporidiosis may be caused by Cryptosporidium parvum. Methods of preventing or decreasing cryptosporidiosis in animals by feeding the hydrogen peroxide-generating compositions to the animals are also disclosed. Some disclosed methods reduce the number of Cryptosporidium oocysts shed by an infected animal or reduce the infectivity of Cryptosporidium oocysts shed by an infected animal. Some methods include feeding the hydrogen peroxide-generating compositions to animals ultimately afflicted with cryptosporidiosis, and the animals gain weight despite the infection.