Upper intestinal mucosal proliferation in the newborn guinea pig: effect of composition of milk feeds.

To examine the effects of first enteral feeds on the development of the gastrointestinal tract, the changes in upper intestinal mucosal morphology and kinetics were studied during the 1st wk of postnatal life in neonatal guinea pigs. Animals were reared either on mother's milk or on a cow's milk formula isocaloric with guinea pig milk. Mucosal crypt-villus architecture was measured by microdissection, and mucosal kinetics were measured using a metaphase arrest technique. Comparable growth was achieved between the two feeding groups. There were no significant differences in the villus heights, crypt depths, or crypt:villus ratios between the naturally fed and formula-fed guinea pigs. The formula fed had a crypt cell production rate twice as high as the naturally fed animals throughout the study period (p less than 0.001). The higher mucosal proliferation rate of the formula-fed animals may be due to the absence of growth-modulating factors in this milk, or a regenerative response to "damage" of the upper intestinal mucosa by cow's milk proteins.