One of the best ways to reduce nitrogen excretion by pigs is to reduce the dietary protein level by supplementing with amino acids.

This requires knowledge of the order in which the amino acids become limiting as dietary protein, and the relative magnitude of difference between that order. This information is fairly well known for corn-soybean meal diets, but is less known for alternative feedstuffs.

To bridge this gap, a user-friendly Microsoft Excel program was designed to identify the limiting amino acids in various combinations of feed ingredients for pigs at all stages of growth, and for gestating and lactating sows.

Various feedstuffs that contribute amino acids are graphically illustrated in the order that they become limiting.

The program converts the dietary concentrations of amino acids to a percentage of the pig's requirement, then regresses those percentages on the inclusion level of the major protein sources in the diet. As the protein source decreases from a level meeting >100% of the pig's amino acid requirements to a level of zero, the regression line for each amino acid intersects a horizontal line, which is set as 100% of the requirement for each amino acid. By following the horizontal line, one can readily assess the order and spacing between the amino acids as they become limiting.

The program applies to amino acids on a total, apparent-digestible or true-digestible basis. An economic component is also included.

With this program, nutritionists can identify potentially limiting amino acids in different feedstuffs or growth stages. It also helps pinpoint the amount of intact protein that can be replaced with amino acids to reduce nitrogen excretion.

An example of how this spreadsheet can be applied is shown in Figure 1.

The program is free of charge and can be accessed at: www.uky.edu/Agriculture/AnimalSciences/swine/AALimitingOrder.html.

Researchers: Gary Cromwell, Beob Kim and Merlin Lindemann, University of Kentucky. Contact Cromwell by phone (859) 257-7534; fax (859) 323-1027; or e-mail gcromwel@uky.edu.