Fate of salmonellas in the alimentary tract of chicks pre‐treated with a mature caecal microflora to increase colonization resistance

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Abstract
Oral challenge with a strain of Salmonella kedougou, resistant to nalidixic acid, gave a time-course for salmonella survival in the alimentary tract of chicks pre-treated with a caecal culture from an eight-week-old bird to increase colonization resistance. In untreated, control chicks, salmonella colonization of the caeca resulted in counts of >106/g within 48 h and a mean generation time of 1.6 h. With treated birds, however, the salmonellas failed to multiply in the caeca and decreased to a low level over a 48-h period, thus suggesting a mainly bacteriostatic effect. Pretreatment of chicks with the caecal culture also reduced the proportion of salmonella-positive crop samples. Growth of the salmonella in a feed-slurry system resembling moistened crop contents occurred rapidly at 37.degree.C but was prevented by addition of the treatment culture, a decline in numbers coinciding with Lactobacillus populations of ca 109/g and a pH value of 5.5. Incorporation of a feed decontaminant, 1% formic acid (pH 4.0), rapidly eliminated both salmonellas and organisms added from the treatment culture.