Fermented liquid feed—Microbial and nutritional aspects and impact on enteric diseases in pigs

The use of liquid feed in pig nutrition has recently gained interest due to several reasons: (1) the political wish of decreasing the use of antibiotics in pig production; (2) the current fluctuations in feed prices what makes liquid feed, with the possibility of using cheap liquid ingredients, an interesting feeding strategy; (3) the policies aiming at increasing production of renewable biofuel with a corresponding increase in liquid co-products from the bioethanol industry, suitable for liquid feeding; (4) environmental policies aiming at decreasing disposal of waste, for example, liquid co-products from the food/pharmaceutical/biofuel industry, that can be included in liquid feeding. In order to obtain fermented liquid feed (FLF) of good microbial quality, that is, biosafe, fresh feed and water are mixed with material from a previous successful fermentation, which acts as inoculum for the new mixture. Several factors affect the microbial and nutritional characteristics of the final product and therefore knowledge on the impact of these factors on the characteristics of the mixture is crucial. The initial hours of incubation are characterized by high pH, low numbers of lactic acid bacteria and yeasts, high numbers of Enterobacteriaceae, and low concentration of lactic acid, whereas at later hours of incubation, the pH decreases, the number of lactic acid bacteria and yeasts, and the concentration of organic acids and ethanol increase, whereas the Enterobacteriaceae counts decrease. A reported undesirable consequence of fermentation is the observed degradation of free lysine and concomitant cadaverine production during fermentation of liquid feed. However, the extent of this degradation is affected by various factors, including feed processing and temperature of incubation. Coliform bacteria are related to free lysine degradation. The possible contribution of other microorganisms present in the FLF to this degradation is uncertain, though. Liquid fermentation has the potential of improving the nutritional value of feed ingredients. Data show that fermentation can improve digestibility of various nutrients, e.g., organic matter, nitrogen, amino acids, fibre, and calcium. The conditions of fermentation and the ingredients used are crucial factors in order to benefit from this, though. Further, there are some strategies that can help improving the microbial and nutritional characteristics of FLF, such as addition of starter cultures, organic acids, or enzymes. Other strategies can help avoiding degradation of the amino acids, like adding the free amino acids immediately prior to feeding. The effect of FLF on gastrointestinal health of pigs is one of the subjects being investigated in the last years. Feeding FLF of good quality results in reduction of the number of enteric pathogens like coliforms and Salmonella, and the few published studies on its effect on important pig diseases like porcine proliferative enteropathy and swine dysentery also indicate reduction of the incidence of these diseases in pigs fed FLF.