Oral administration of defined mixtures of bacterial isolates from fecal and cecal contents of adult chickens protected young chicks against infection with Salmonella. One-day-old chicks were treated with mixtures containing 50, 40, 25 and 10 bacterial isolates and challenged 2 d later with 104, 105 and 106 colony-forming units of nalidixic acid-resistant Salmonella typhimurium. The chicks were examined for infection 6 d after challenge. The mixture of 50 bacterial cultures gave protection comparable to that obtained with fecal or cecal cultures of unknown bacterial composition. Less protection was evident with mixtures containing fewer cultures.

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