Protein and amino acid nutrition of lactating dairy cattle—today and tomorrow

The Cornell Net Carbohydrate and Protein System was used to (1) estimate absorbed amino acids provided by rumen escape protein and (2) formulate rations on the basis of amino acids. Forages, even those high in crude protein, only provide small amounts of rumen escape amino acids. Maize proteins are deficient in lysine. Oil seed proteins contain low levels of methionine. Animal and marine proteins, because of their high crude protein and low ruminal degradation, can be used to adjust the amino acid profile of absorbed protein, especially methionine (fish meal) and lysine (blood meal) Rations to support high levels of milk production need to contain protein sources with amino acid profiles that are complementary.