Microbial and nutritional characteristics of pig liquid feed during fermentation

An in vitro study was performed with the aim of describing the course of fermentation of pig liquid feed during incubation, including microbial characteristics and amino acid concentration in the mixture. A standard grower diet with added 2.0 g lysine/kg, 2.0 g methionine/kg, and 2.5 g threonine/kg was formulated. Three experimental treatments were prepared: (1) the grower diet with added amino acids, ‘control’; (2) the grower diet with added amino acids +4.8 g solid acidifier Boliflor® FA 2300 S/kg liquid feed, ‘FA2300S’; (3) the grower diet with added amino acids +2.0 g formic acid/kg liquid feed, ‘formic’. Feed and water were mixed in the ratio 1–2.75, and incubated in bioreactors with a volume of 1 L at 20 °C. The samples were incubated during 48 h, during which no feed or water was removed or added. A sample was taken after 0, 6, 24, and 48 h of incubation. After 48 h of incubation, 90% of the mixture was removed and replaced with fresh feed and water, and the same procedure was followed at 55, 72, 79, and 96 h of incubation. A sample was taken at 96, 102, and 108 h of incubation. Enterobacteriaceae counts in the ‘control’ diet increased from time 0 to time 24 h of incubation, and decreased at time 48 h. The Enterobacteriaceae counts in the ‘FA2300S’ and ‘formic’ diets decreased with time of incubation during the first 48 h to levels between <3.0 and 3.3 log cfu/g sample. From 96 to 108 h of incubation, the Enterobacteriaceae counts decreased in all three diets, being lowest in the ‘formic’ diet at all three sampling times and highest in the ‘control’ diet. The concentration of total and free lysine (g/kg crude protein), threonine, and methionine decreased with time of incubation in all diets. From 96 to 108 h of incubation, ∼5 to 9% total lysine, ∼12 to 13% total threonine, and ∼17 to 19% total methionine had been degraded. During the same incubation time, ∼26–34% free lysine, ∼31–38% free threonine, and ∼31–42% free methionine had disappeared. Addition of 2.0 g formic acid/kg pig liquid feed or 4.8 g Boliflor® FA 2300 S/kg pig liquid feed are strategies that impede the proliferation of Enterobacteriaceae during the first hours of fermentation but have no effect on amino acid degradation. A disappearance of, mainly, free amino acids occurs during fermentation of liquid feed as prepared in the present study.