Investigations have been carried out to find out whether immunoglobulins or glycoproteins are responsible for these effects. Another approach is the specific amino acid composition of these protein sources. In human clinical feeding attention is paid to the role of amino acids in patients recovering from operations. In 1996, researchers found that glutamine supplementation prevented jejuna atrophy (as indicated by villus height) during the first week post weaning and improved the feed conversion ratio by 25% during the second week post weaning.