All pigs require protein, which consists of amino acids.
Amino acids are used for maintenance, growth, gestation, and lactation. Pigs actually do not have a protein requirement, but quality protein provides the amino acids which are required. While some amino acids are synthesized by the animal, the essential ones cannot be synthesized at a rapid enough rate to permit normal growth. These must be provided in the feed. See Table 1 for the essential amino acids and their requirements for growing and finishing pigs.