Development of the normal gastrointestinal microflora of specific pathogen-free chickens.

The development of the normal intestinal microflora of the small intestine, caecum and large intestine of specific pathogen-free (SPF) chickens, was studied in the period from hatching to 84 days of age. No bacteria were detected in any of the sites at hatchery (day 1), but by day 3 significant levels of faecal streptococci and coliforms were isolated from all sites. The flora of the small intestine was limited to faecal streptococci and coliforms for the first 40 days and then lactobacilli became established and dominated the flora. A large variety of facultative and strictly anaerobic organisms colonized the caecum. Many of these species were transient and were only present for a limited period; after 40 days the flora stabilized to consist predominantly of faecal streptococci, Escherichia coli, Bacteroides spp. and Lactobacillus sp. The flora of the large intestine was composed of organisms also present in the small intestine or the caecum. These findings differ from previously published studies on conventionally reared chickens in that the number of species isolated and the population levels of organisms are much lower. This probably reflects the absence of continuous environmental challenge to the chickens because of the housing and feeding facilities in which the chickens were maintained.