There's little doubt that determining lysine requirements has become an integral part of your nutrition program, but determining what level of lysine to add is the challenge.

Research at Kansas State University looks at varying lysine levels, not just in terms of performance improvement, but also from an economic perspective, in order to show which level returns the most to your pocket.

The research involved 2,400 grow/finish pigs, with gilts and barrows fed separately. There were four different lsyine-to-calorie ratio (LCR) regimens, both with and without added fat. Both groups were fed in four phases, each lasting for 28 days. (See accompanying table.)

It's not clear what effect more or fewer feeding phases would have had on the experiment. As the pigs grow, the LCR requirements drop, so having more phases would have allowed researchers to more closely target lysine levels, but that may or may not have shown statistical differences.

In gilts, average daily gain and feed efficiencies were not significantly higher in the LCR 4 diet over the LCR 3 diet. Barrows, however, told a different story with the greatest gains coming from the LCR 4 diet.

Add in carcass information and economic factors, and the LCR 4 diet soon becomes the most favorable diet across the board, says Steve Dritz, Kansas State University nutritionist. That doesn't necessarily mean that the higher the lysine levels the better the returns in all cases.

"The best lysine-to-calorie ratio depends on your herd's genetic potential, environment, health status and other factors," says Dritz. "It's important to use the Kansas State or National Research Council guidelines or do your own research."

Dritz says in a perfect world, setting up your own research barns to do lysine titrations would be ideal, but it is not cost-efficient for most operations. The next best thing would be to set up ultrasound tests and develop your own lean-growth curves. This will allow you to develop the dynamics of different LCR's. If ultrasound is not possible, then Dritz recommends using the standard recommendations provided by the NRC or in publications such as the Kansas Swine Nutrition Guide in consultation with a swine nutritionist.

"Producers will have a hard time evaluating their pigs' lysine needs just by looking at them," says Dritz. Again, his preference is to utilize ultrasound, research or at the very least – studying the kill sheets. Specifically, he suggests looking at backfat levels. If they're too high your LCR may be too low.

Whatever information you use, you'll make decisions based on whether it's economical to your operation.

To determine the most economical lysine level, the researchers used income over feed costs, using the 10-year-average for each month.

To determine income, the experiment used two separate packer grids: one with a fixed premium, the other with a premium as a percentage of the base price.

"We used these two grids because we think they represent the majority of packer grids out there," says Dritz.

As with anything, not every operation will be the same when it comes to maximizing the economic returns of lysine levels. To figure out which level is best suited for your farm use the Kansas State or NRC guidelines, or consult a swine specialist or nutritionist.