Postnatal changes in bacterial populations in the gastrointestinal tract of dogs.

OBJECTIVE: To describe postnatal changes in the populations of bacteria in the gastrointestinal tract (GIT) of dogs. ANIMALS: 110 Beagles ranging from neonatal to adult dogs. PROCEDURE: Contents of the stomach and proximal and distal portions of the colon and contents and mucosa of the mid region of the small intestine were collected from puppies at 1 day after birth and subsequent suckling; puppies at 21, 42, and 63 days after birth; and adult female dogs (ie, dams of the puppies) for enumeration of bacterial populations.
RESULTS: The entire GIT was colonized at day 1 by all groups of bacteria studied; aerotolerant forms were dominant. During subsequent postnatal development, there were changes in the relative proportions of the various groups of bacteria with anaerobic groups increasing in absolute and relative numbers. CONCLUSIONS AND CLINICAL RELEVANCE: Establishment of bacterial populations in the GIT of dogs is a gradual process that begins immediately after birth. Age-related changes in the relative proportions of bacterial groups coincided with changes in diet and physiologic processes of the host and can influence nutritional state and disease resistance of developing dogs. Differences among regions of the GIT suggest that fecal samples may have limited use for understanding the populations of bacteria and the age and diet-related changes in various regions of the GIT.