Artificial formula induces precocious maturation of the small intestine of artificially reared suckling rats

Background: The artificially reared rat model was used successfully to study the effect of nutrition during the early postnatal period on growth and development of the neonate. Over-growth and morphologic changes of the gastrointestinal tract are known consequences of artificial rearing. The major goal of our study was to elucidate whether artificial rearing-enhanced gut development is caused by artificial diet or by gastrostomy and the artificial rearing technique itself. Methods: Suckling rats at day 8 of age underwent intragastric cannulation and were machine fed either a cow's milk-based artificial rat's milk substitute or pooled rat's milk for 4 days. Dam-fed littermates served as a control. Results: Body growth did not differ in the three experimental groups. In rats receiving rat's milk substitute, small intestinal wet weight was approximately 60% greater than in rats fed rat's milk or control rats. Additionally, the entire small intestine was approximately 20% longer in the rat's milk substitute group. Morphologically, rat's milk substitute-fed pups demonstrated significantly greater intestinal villus length and crypt depth compared with rat's milk-fed or control rats. Jejunum and mid-jejunum of the rat's milk and control groups did not differ in these parameters. Intestinal sucrase activity of rat's milk substitute-fed rats was significantly elevated compared with rat's milk-fed rats or control animals. Conclusions: These results indicate that cow's milk-based formula, not gastrostomy or artificial feeding technique, is a principal cause of the small intestine overgrowth and precocious maturation of some intestinal functions observed in artificially reared sucklings. (C) 2000 Lippincott Williams and Wilkins, Inc.