Abstract. Title ofthe paper: The efficiency of utilization of intestinal digestible indispensable amino aeids in growing bulls
There are problems to determine the efficiency of protein deposition of intestinal absorbed amino aeids, because it cannot be exeluded that the amount of single or some indispensable amino acid (IAA) can influence the growing Performance of the animal. The dependence of amino acid gain on the flux of essential absorbable amino aeids into the duodenum was studied in growing bulls to calculate the utilization rate of these amino aeids. Four growing bulls (Schwarzbuntes Milchrind, BW: 240–310 kg) with duodenal T-type cannulas were fed diets varying in crude protein content. Energy level was 11,2 MJ ME/kg DM. The efficiency for the different absorbable IAA was decreased with increasing nutritional level. This is in contrast with the constant utilization factor ofthe protein evaluation system (AfB, 1995; 1997). The efficiency of utilization of apparently digestible IAA for protein retention was highest for His and Met and amounted to 33 (He), 34 (Phe and Thr), 38 (Lys and Val), 41 (Leu), 52 (Met) und 76 (His) %, respectively. The intersection ofthe regression curve (AA-deposition against apparently digestible AA) with the abscissae resulted in the maintenance requirement of absorbable amino acid. For growing bulls (BW: 300 kg) a value of 4,7 g/d histidine and 4,2 g/d methionine was determined, but more investigations are necessary in this field.