Age of cattle as related to resistance to infection with Mycobacterium paratuberculosis

Two 1-month-old calves, four 9-month old calves, and 4 adult (5 to 11 years old) cattle were exposed to Mycobacterium paratuberculosis. At 150 days after exposure, all cattle were killed and necropsied, and at that time, tissues of the 1-month-old calves had more bacilli and lesions than did tissues of the 9-month-old calves or the adult cattle. All cattle responded to immunologic tests during the experiment.