Lysine and protein levels in corn-soybean meal diets for growing-finishing swine.

Previous work with growing swine indicated that the lysine requirement, expressed as a percentage of the diet, decreased by .02 percentage units with each 1% reduction in dietary protein level. Thus, the dietary lysine needed for optimal performance may be less than the reported requirement when a portion of the soybean meal in a corn-soybean meal diet is replaced with crystalline lysine. An experiment was conducted to test this concept in each of three phases of growth: growing (23.6 to 47.2 kg), early finishing (47.2 to 74.8 kg) and late finishing (74.8 to 92.8 kg). Dietary crude protein levels were 16, 13 and 12% for the positive control regimen and 14, 11.5 and 11% for the negative control regimen during the growing, early finishing and late finishing periods, respectively. In each phase of growth, regimen 1 was the positive control; regimen 2 was the negative control plus lysine to the level in the positive control; regimen 3 was the negative control plus lysine to the level in the positive control less .02% lysine for each 1% decrease in crude protein from the positive control level; and regimen 4 was the negative control. Ninety-six crossbred pigs were used to form two barrow and two gilts replicates with six pigs per pen-replicate. Average daily gains summarized over the entire growing-finishing period were .74, .75, .75 and .65 kg per day for regimens 1, 2, 3 and 4, respectively. Corresponding gain to feed ratios were .29, .29, .30 and .26. Within each growth phase, average daily gain and gain to feed ratio followed patterns similar to the overall results. Carcass evaluation of barrows indicated a trend toward leaner carcasses from pigs on regimens 1, 2 and 3 than from those on regimen 4. Thus, the lysine requirement can be reduced when crude protein levels are reduced by replacing soybean meal with synthetic lysine.