Conclusion
Addition of 2.0 g formic acid/kg liquid feed or 4.8 g Boliflor® FA 2300 S/kg liquid feed to pig liquid feed are strategies that impede the proliferation of Enterobacteriaceae during the first hours of fermentation. A disappearance of free amino acids occurs during fermentation of liquid feed as carried out here. However, although addition of formic acid or Boliflor® FA2300S to the liquid feed decreases the microbial density in the mixture, they do not attenuate the disappearance of amino acids. Further studies are needed in which identification of the microbial population in FLF to strain level is carried out concomitantly with quantification of metabolites from carbohydrate and amino acid fermentation. With this knowledge, strategies that promote beneficial strains and that impede the proliferation of undesired strains resulting in FLF with optimal microbial and nutrional characteristics will be much easier to establish.