In most AA digestibility experiments collection bags are changed at least every 30 min and the collected ileal digesta are stored at –20 °C to prevent microbial degradation of proteins. Other attempts to reduce microbial activity in digesta include adding acids to collection bags to reduce the pH in ileal digesta. Acids may also be added to collection pitchers. However, in some experiments, no attempt to reduce pH is made because it is assumed that the rapid reduction in temperature after collection is sufficient to prevent microbial degradation of proteins.

To our knowledge, there is, however, no information about the necessity of adding acids to collected digesta and it is not known if values for apparent ileal digestibility (AID), basal endogenous losses of AA, or standardized ileal digestibility (SID) of AA are influenced by addition of acids to digesta. Therefore, the objective of this experiment was to test the null-hypothesis that values for AID, basal endogenous losses, and SID of AA are not influenced by addition of acids to ileal digesta collection bags or to collection pitchers.