To investigate what factors lead to rapid postnatal tissue growth and functional maturation in the newborn intestine, we compared intestinal tissue mass and digestive enzyme activities between newborn unsuckled piglets and piglets bottle fed for 3 days with either 5% lactose solution, intact porcine colostrum or trypsinized porcine colostrum. Bottle feeding of colostrum or trypsinized colostrum, but not lactose solution, led to a significant increase in the weight and length of the small intestine (p < 0.01) and a significant increase in the mucosal weight of the large intestine (p < 0.05). The mucosal protein content in the small and large intestine and the mucosal DNA content in the large intestine increased significantly following 3 days of bottle feeding of porcine colostrum or trypsinized colostrum. The total mucosal DNA contents in the small intestine of piglets fed colostrum or trypsinized colostrum were, respectively, 39 and 64% greater than that in the newborn unsuckled piglets. Intestinal digestive enzymes showed a differential response to the dietary treatment. Bottle feeding of intact porcine colostrum, but not trypsinized porcine colostrum led to a significant increase in lactase- and alkaline phosphatase-specific activities in the small intestine, while bottle feeding of lactose solution led to a significant decrease in the specific activity of lactase. In contrast, the specific activity of maltase in the small intestine increased significantly with age irrespective of dietary treatment. These results indicate that genetic and dietary factors are involved in regulating postnatal intestinal development, and porcine colostrum contains a trypsin-labile component which can increase lactase and alkaline phosphatase activities in the newborn intestine.