Effect of acid addition to pig liquid feed on its microbial and nutritional characteristics

An in vitro study was performed to describe the effect of addition of acid products to liquid feed on the course of fermentation. A standard grower diet with added extra lysine, methionine, and threonine was formulated. Three experimental treatments were prepared: the grower diet, ‘Control’; the grower diet+4.8 g solid acidifier Boliflor® FA 2300S/kg liquid feed, ‘FA2300S’; and the grower diet+2.0 g formic acid/kg liquid feed, ‘Formic’. Feed and water (1 to 2.75) were incubated in bioreactors with a volume of 1 l at 20 °C. A sample was taken after 0, 6, 24, and 48 h of incubation. After 48, 55, 72, 79, and 96 h of incubation, 90% of the mixture was removed and replaced with fresh feed and water. A sample was taken at 96, 102, and 108 h of incubation. Enterobacteriaceae counts were highest in the ‘Control’ diet and lowest in the ‘Formic’ diet at all sampling times. From 96 to 108 h of incubation, ∼5–19% total lysine, threonine, and methionine, and ∼26–42% free lysine, threonine, and methionine disappeared. Addition of 2.0 g formic acid or 4.8 g Boliflor® FA 2300S per kg pig liquid feed impeded a blooming of Enterobacteriaceae during the first hours of fermentation but had no effect on amino acid degradation. A disappearance of, mainly, free amino acids occurred during fermentation of liquid feed as prepared in the present study.