Nine weaned Holstein calves (139 ± 2.4kg) fitted with duodenal cannulas were used in a completly ramdomized design to study the effects of supplemental protein sources (2% of urea or 10% of meat meal) of high concentrate diets (corn and soybean meal) on site and extent of digestion of feed, in ad libitum feeding conditions. The forage:concentrate ratio was 30:70. The ruminal and total digestibility of dry matter, organic matter and nitrogen, as well as microbial and feed residual nitrogen duodenal flow, and the microbial protein synthesis efficiency were similar for both treatments (P>0.10). The ruminal digestibility of starch was also similar, but total digestibility was lower for urea treatment (P<0.10). However, this is probably due more to the limited capacity of ruminants to digest starch in the intestines than to an effect of the protein supplement. The use of urea or meat meal, as supplemental protein sources for corn and soybean meal based diets, formulated to supply the growth requirements of calves fed ad libitum, did not affect the digestion process.Thus, the choise of the protein supplement do not depend on nutritionals reasons.
bacterial protein synthesis; digestibility; intake; meat meal; urea
