A comprehensive study of how age and weaning affect intestinal structure and enterocyte ability to digest and absorb nutrients has been carried out in 4- and 6-week-old piglets.
Villus length, which did not change significantly in unweaned piglets 4–6 weeks after birth, was halved 5 days after weaning. Crypt depth, which increased normally in unweaned piglets, is further increased by weaning in both 4- and 6-week-old animals.
Lactase activity, which decreased normally with age, was inhibited more than a-glucosidase by weaning. Weaning of 6-week-old piglets also caused a significant increase in maltase II and III activities. Alkaline phosphatase activity was unaffected by age or weaning in 4- and 6-week-old piglet intestine.
Na-dependent alanine transport was reduced in 6- compared with 4-week-old unweaned piglet intestine. Weaning inhibited Na-dependent alanine transport in 4- but not 6-week-old pigs. Na-independent alanine transport, which was considerably less than that found in the presence of Na, was not noticeably affected by age or weaning.
Weaning-induced problems in intestinal function appear from the present results to be caused more by changes in intestinal structure and specific loss of digestive enzymes rather than by any gross change in absorptive function. The possible role of immune as well as nutritional factors in causing these weaning-dependent changes in intestinal function is discussed.