Abstract: To determine the effects of milk replacer with different processed soy protein on the activities of digestive enzyme and the development of small intestine, 18 new-born calves were divided into three groups each with 6 duplicates, calves in group A, B and C were fed milk replacers contained heated full-fat soybean flour, defatted soybean flour or extruded soybean flour, seperatelly. The experiment was conducted for a 7 d adaptation period and a 42 d treatment period. The results showed that milk repalcer with different processed soy protein could affect the digestive enzyme activities and intestinal morphology. Compared to that of group A and C, the activities of trypsin and chymotrypsin were lowest in group B. Villus heigh was similar among groups in the proximal jejunum(P>0.05),but it were higher for group A and C than group B in other site of small intestine. Recess depth was similar among groups in the duodenum and the proximal jejunum(P>0.05). the ratio of villus height to recess depth were higher in group A and C that that of group B(P<0.05).there was no difference of mucosa thickness among groups in the duodenum and proximal , middle jejunum(P>0.05),but in the far-end of jejunum, it was higher in group A and C than group B (P<0.05).Therefore, full-fat soybean flour and extruded soybean flour could be used in milk replacer of calves.

Key words: calf; milk replacer; protein; digestive enzyme