A feed supplement for increasing the plasma amino acid level of animals, including animal feed and liquid lysine base, where the liquid lysine base has a concentration between about 45% and about 55%, and has a pH level of between about 9.5 and about 10.5, a chloride content between about 0.10% and about 0.15%, a bulk density of between about 1.14 and about 1.17 g/cm.sup.3, and a maximum moisture level of between about 42% and about 48%. The animal feed may either be dry feed, liquid feed, drinking water or milk replacers, or a combination thereof. The present invention also includes a method of increasing the plasma amino acid level of animals, including the steps of providing animal feed, and supplementing the animal feed with an amino acid supplement comprising liquid lysine base having a concentration between about 45% and about 55%, and having a pH level of between about 9.5 and about 10.5.