Lysine and Protein Levels in Corn-soybean M E a L Diets

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 i, 2, 3 and 4, respectively. Corresponding gain to feed ratios were .29, .29, .30 and .26. Within each growth phase, average