The use of protease enzyme alone increased the dietary AID of N in the current study indicating that a greater proportion of N from the diet became available in the small intestine with dietary inclusion of protease. As the availability of protein post-caecum is considered to be negligible, being degraded through fermentation in the large intestine, an improvement in AID of N can be interpreted as beneficial, as it suggests more protein is available to meet the growth demands of the pig. In this study, the DDGS and RSM-based basal diet was formulated to contain adequate concentrations of AID Lys and other limiting essential amino acids appropriate for the age and growth rate of the pigs used in the study, as recommended by the National Research Council (NRC, 1998). In terms of variation, the standard error of the mean for the AID of N using the slaughter technique in this experiment was approximately 8% of the mean. This is slightly higher, but comparable with the variation (approx. 4%) observed with cannulated pigs