Weaning represents a stressful period for piglets causing gut health challenges including post-weaning diarrhea (PWD). Antimicrobial growth promoters (AGP) and zinc oxide (ZnO) have been used in weaned pig diets to control the incidence of diarrhea; however, the use of in-feed AGP and ZnO has been or will be banned in many countries due to raising public concerns on the potential risks of antibiotic resistant bacteria for human health or heavy metal accumulation in the environment (Alexopoulos et al., 2004; Kemper, 2008; Li et al., 2015; Park et al., 2017; Hejna et al., 2021). Thus, there is a need for the industry to develop feed additives or nutritional concepts that can be used as alternatives to in-feed antibiotics or as part of a combined solution to ZnO replacement (Pettigrew, 2006; Stein and Kil, 2006).
Some of these feed additives include prebiotics, probiotics, symbiotics, organic acids, bacteriophages, essential oils, and phytobiotics (Heo et al., 2013; Thacker, 2013; Suiryanrayna and Ramana, 2015; Kim et al., 2017). For this AMINONews review article part 2, the application of probiotics and organic acids are summarized because we consider that these two feed additives have a high impact for improving the gut health of piglets. However, the other feed additives should not be ignored and may be considered as alternative sources depending on the production system of the individual producers.