Digestibility of Individual Amino Acids in Rumen Microbial Protein and Undegraded Dietary Protein in the Small Intestine of Sheep

Abstract

Digestibility of individual amino acids in the small intestine of sheep was estimated on four different batches of rumen microbial protein, on soybean meal and 0.5% formaldehyde treated soybean meal and on six different samples of undegraded dietary protein. The digestibility of the individual amino acids in the four different isolates of rumen bacteria was not significantly different and a mean value for the individual amino acids was calculated. The lowest digestibility of 0.40 was observed for diaminopimelic acid (DAPA), but also phenylalanine (0.69) and cystine (0.75) showed lower digestibilities than the remainder, which varied between 0.80 and 0.91. Treating soybean meal with 0.5% formaldehyde reduced the digestibility of the majority of the amino acids compared to original soybean meal. For phenylalanine the reduction was 0.24 digestion units and the average reduction was found to be 0.13 digestion units. Among the different undegraded protein sources tested, significant differences were observed with respect to digestibility of individual amino acids. Also within the different undegraded proteins large variations were observed in the digestibility of individual amino acids. These results indicate that undegraded proteins differ in their potential as a source for absorbable amino acids in the small intestine.