Effect of weaning age on the small intestine mucosa of rats.

Weaning of mammalian progeny is associated with a change in food composition and mother-offspring separation. Weaning results in a critical period of low voluntary feed intake, during which the animal is adapting to the starter diet. To evaluate the effects of weaning age on morphological changes that occur in the intestines of rats, we assessed intestinal histomorphometry and somatic growth in 21-days-old pups and 90-days-old mature rats that had been weaned early (day 16), normally (day 21), or late (day 26). Early weaning resulted in deeper crypts, lower villous/crypt ratio, and a smaller villous area on day 21. Crown-tail length correlated positively with the crypt depth and negatively with the villous/crypt ratio. At age 90 days, early weaned animals had shallower crypts, a greater villous/crypt ratio, and a smaller villous area compared with their normally weaned counterparts. The rats' crown-tail length correlated negatively with the crypt depth and positively with the villous/crypt ratio. Early weaning significantly affects the intestinal mucosa, which may impact food absorption and lead to differences in somatic growth compared with late weaning. Over time there may be a phase of compensation with increased villus height and crypt depth.