There is no number that works everywhere: That is the first thing to admit when talking about low-protein diets for piglets. The practical limit is not set by fashion, nor by how low somebody managed to go in a conference paper. It is set by how well the diet delivers the amino acids, digestibility, palatability and feed intake that young pigs need.
In theory, crude protein can come down if the amino acid profile is corrected properly. In practice, the room for error gets smaller with every point you remove. Piglets are not forgiving. A nursery formula that looks elegant on software can still disappoint if the synthetic amino acid program becomes too narrow, if nonessential nitrogen becomes limiting, or if the remaining protein sources are less digestible than expected.
