The impact of amino acid deficiency in birds is eloquently shown when imbalanced mixtures are infused into either the carotid artery or the jugular vein. When infused into the carotid the mixture goes immediately to the brain regulatory sensors, and feed intake is reduced. When infused into the jugular, there is little impact on feed intake, since the liver has the chance to intervene and rebalance the amino acids before they eventually reach the brain sensors.