The utilization of dietary amino acids in commercial pig production is relatively low. An experiment done on gilts weighing 50 kg and 6 different diets were given; on average the ingested dietary protein was utilized with a 30% efficiency and on average the lysine was utilized with an efficiency lower than 45%. Different physiological processes contribute to the incomplete utilization of the amino acid (excretion of unabsorbed dietary AA, absorption of chemically-unavailable compounds derived from AAs, use of Aas for body protein maintenance, use of AA for the synthesis of non-protein N compounds, preferential catabolism of AAs for energy supply, inevitable AA catabolism and catabolism of Aas supplied above the amount required for the maximum rate of protein retention). The development of AAs digestibility assays is also presented. Improvement in the digestibility of AAs is needed and will probably come through a better understanding of the processes involved.

The processes and methods involved in Aas digestibility and digestibility assays are complex and complicated. Fundamental work is needed to investigate the reactions and physiological processes involved.