To address the current shortage of feed-grade L-threonine, we need to consider natural sources of this amino acid.
Threonine is also one of the most limiting amino acids, meaning that it exists in relative limited amounts relative to animal needs for this amino acid. In fact, in poultry it is third limiting after methionine (along with cysteine) and lysine, which are first and second limiting amino acids, respectively. In pigs, threonine is second limiting after lysine and it is followed by methionine. Birds need more methionine and cysteine (the sulfur-containing amino acids) because their feathers contain an excessive amount of these amino acids.