Amino acids are the building blocks for protein. All animals need amino acids for maintenance and growth of muscular tissue (body protein). In total 20 amino acids form the building blocks for protein. Nine of these amino acids cannot be synthesized by the animal itself and have to be supplied via the feed. These are called the essential amino acids. The other are non-essential amino acids and can be made by the animal itself from dietary protein. Besides the use for protein synthesis, amino acids are also required for other metabolic functions like development of organs and optimal functioning of the immune system.