In recent research at Iowa State University, including lysine, alone, in swine diets resulted in a reduction of dietary crude protein from 17.4% to 17%. Adding lysine, methionine, threonin and tryptophan to the diet reduced crude protein content even further, to 14.5%. Incorporation of lysine and methionine, though not tested in this study, would have resulted in a dietary crude protein content of approximately 16.2%. The reduced diet content does translate into less manure excretion. Urine nitrogen, where most of the nitrogen is excreted, decreased by 15% by adding the four amino acids. In addition, ammonia emissions were reduced by half. Others have demonstrated similar results. Similar results would be expected following feeding to poultry. However, data that addresses the combined use of lysine and methionine for poultry or swine is somewhat limited.
Nutrient excretion reductions will be site-specific based on how the amino acids are formulated in the diet and which amino acids are used. Producers who want to see how such practices affect their manure values should plan to test their manure before and after implementing such a change. If the change in diet formulation has already taken place, producers should still test their manure to see how composition in their manure storage facility compares to values used by a producer in his/her manure management plan. The change in nitrogen content may have a positive effect on manure management planning.