In ca�le, energy-rich feeding causes an increase in the size of rumen papillae and leads to considerable mucosa proliferation (Dirksen et al., 1984). In animals fed low and high energy diets rumen mucosa revealed progressive reduction and intensive proliferation, respectively (Dirksen et al., 1985). Intensity of rumen fermentation increases with the increasing intake of concentrate and simultaneously the occurring volatile fa�y acids promote the structural development of the rumen epithelium (Kauffold et al., 1977;Hofmann and Schnorr, 1982;Zitnan et al., 1998).So far, insufficient or no investigations at all have been carried out into the effects of the diet upon the development of small intestinal mucosa.According to Tivey and Smith (1989), changes in the development of enterocytes and in the structure of villi determine the digestive and absorptive capacity of the small intestine. Kreikemeier et al. (1990) studied the activity of carbohydrate digesting enzymes in Holstein and Longhorn bulls and observed it to be influenced by the type of diet and the level of feed intake. Mir et al. (1997) considered the length of villi and crypts and mucosal carbohydrase activity to be an important factor in nutrient absorption; they recorded differences in these parameters between different cattle breeds, of which Holstein bulls had the highest lactase activity and the longest villi in the middle part of the intestine. ABSTRACT: This study examined the effects of extensive and intensive feeding on the morphology of the gastrointestinal tract as well as on the level of carbohydrase activity in the small intestine of growing ca�le. Fourteen growing male bulls aged 5 months were divided into two feeding groups. The extensively fed animals were kept on pasture in the summer and in a stall in the winter whereas the intensively fed group was housed all the year long. The bulls were slaughtered 16 h a�er the last feeding at the age of 18 months. Rumen fluid samples and mucosa samples from the ventral ruminal sac and the intestinal tract (duodenum, jejunum, ileum) were subjected to analyses. Evaluation of rumen fermentation did not reveal significant differences between the groups, however, the molar proportions of propionic acid were increased in the intensively reared bulls. As to the activity of the individual carbohydrase enzymes (maltase, cellobiase, lactase) no significant differences could be stated between the groups. Comparison to the extensively reared group revealed that the length and width of papillae of the ventral ruminal sac was significantly increased in the intensively reared animals (P < 0.001) and so was the papillar surface per cm 2 of mucosa (P < 0.001). The length of duodenal villi in the intensive group was singnificantly increased (P = 0.026) whereas that of the jejuenal villi approached the limits of significance (P = 0.052) when compared to the extensive group. There were no significant differences in the depth of crypts, however, the crypts of the intensively reared animals were somewhat deeper. The lengt...