The effect of controlled fermentation on the fate of synthetic lysine in liquid diets for pigs

Crystalline lysine is frequently added to pig diets to provide the correct amino acid balance. Recent studies have shown that free lysine can be lost when liquid pig feed is fermented with lactic acid bacteria (LAB). The metabolism of lysine was examined, over 72 h, in uninoculated liquid feed (Control) and in liquid feed inoculated with lactic acid bacteria (LAB) (Lactobacillus plantarum and Pediococcus acidilactici); or Escherichia coli and combinations of LAB and E. coli. In the Control and the fermentations that included E. coli, lysine was rapidly metabolised, with ca. 90% degraded in 21 h. The production of cadaverine accounted for ca. half of the lysine lost. There was no loss of lysine in the LAB fermentations and no cadaverine was produced. Combining E. coli and LAB resulted in a loss of ca. 20% lysine in the first 7 h with no further metabolism thereafter. Cadaverine produced in these fermentations accounted for all of the lysine lost. The rate of lysine metabolism was inhibited by the increase in lactic acid present in the fermentations. Fermenting E. coli and LAB with the addition of 50 mM lactic acid at 0 h resulted in the lysine levels remaining unaltered throughout the fermentation period. These results imply that the loss of lysine from fermented liquid pig diets is due to the metabolism of lysine by E. coli before they are eliminated from the diet by the increasing acidity resulting from LAB fermentation.