In a first experiment with 24 newborn lambs, the promoting effect of colostrum feeding on the fresh weight of the small intestine and its protein content was demonstrated by comparison with that of other dietary treatments (fasting, lactose, protein hydrolysate feeding). In a second experiment, the amounts of colostral IgG1 entrapped within the intestine wall and the valine incorporation rates into the intestinal protein were determined in 3-, 8- and 18-hour-old lambs fed either cow milk, cow colostrum or ewe colostrum. The amounts of IgG1 in the small intestine wall and the valine incorporation rates were higher in the lambs fed colostrum (ewe or cow) than in the milk-fed animals. The intestinal protein increase resulted primarily from the retention of colostral proteins in the colostrum-fed newborn lambs. However, colostrum feeding stimulated intestinal protein synthesis more actively than milk feeding.