The isoleucine requirement of the weanling pig

The current standards or estimates of the essential amino acid requirements of swine are based almost wholly on growth trials. These were carried out with groups of three or four pigs fed individually on semisynthetic diets. The trials generally lasted for only 30–35 days since several expensive amino acids were being fed. The main criticism is that the values given were not adequately substantiated by carrying out nitrogen-balance determinations. It is also possible that the nitrogen-retention values might have led to different conclusions from those arrived at on the basis of the growth trials only. The standards must remain tentative until tested with a larger number of animals and until many more nitrogenbalance determinations have been carried out.