The building blocks of all protein, whether from dairy or plant sources, are essential amino acids, and they are needed for energy, tissue growth and repair, digestion, metabolism and the production of antibodies. The branched chain amino acids (BCAAs) are metabolized within the muscles; all other amino acids are metabolized in the liver.
We can compare various protein sources based on how many amino acids they contain. High quality dairy, unlike most plant proteins, is considered a complete protein because it is made of all 9 essential amino acids. Dairy protein also contains higher levels of BCAAs compared to all plant proteins, which is especially helpful for repairing and maintaining muscle mass.
According to The Protein Digestibility Corrected Amino Acid Score (PDCAAS), dairy ranks highest among all protein sources, making it the most absorbable and useable form of a complete protein source.