To evaluate the effects of lactylate and Bacillus subtilis on growth performance, complete blood cell count, and microbial changes, 264 weaning pigs were assigned to four treatments (1) control (Con) basal diets that met the nutrient requirement for each phase, (2) 0.2% lactylate (LA), (3) 0.05% Bacillus subtilis strains mixtures (BM), or (4) the combination of LA and BM (LA+BM) added to the control basal diet at their respective inclusion rates in each of the three phases. Dietary lactylate tended to increase weight gain, significantly increased feed intake, and reduced fecal total E. coli and enterotoxigenic E. coli counts during Phase 1. Pigs fed Bacillus subtilis had a greater gain to feed ratio (G:F) during Phases 1 and 2. Pigs fed lactylate had an increased peripheral absolute neutrophil count on D14 but a decreased eosinophil percentage. Pigs fed Bacillus subtilis had an elevated peripheral total white blood cell count at study completion. The addition of lactylate increased microbiota richness, reduced E. coli, and increased Prevotella, Christensenellaceae, and Succinivibrio. Bacillus subtilis supplementation-enriched f_Ruminococcaceae_unclassified and S24-7_ unclassified had positive relationships with feed efficiency. Collectively, these findings suggested that lactylate can be added to diets to balance gut microbiota and improve growth performance during the early postweaning period. The combination of lactylate and Bacillus subtilis strains exerted a synergic effect on the growth performance of nursery pigs.

It is well known that the inflammatory process has a profound impact on growth and metabolism. As early as the late 1990’s, Spurlock (1997) recognized that immune system activation in response to a pathogenic challenge occurred at the expense of energy resources for growth and productivity in livestock and poultry. This interface between immunology and metabolism has been further investigated, both at the cellular level related to the nutrient partitioning to support immune cell activation and the systemic level related to the partitioning of nutrients for tissue growth or turnover. Knowledge in the field of immunometabolism has made significant progress over the past 25 years with the development of investigative tools in genomics and molecular biology, such that there is a good mechanistic understanding at the cellular and tissue level of how immunity influences metabolic processes. Most lacking is an understanding of the intrinsic and external signals that instigate the immune response and the resulting metabolic changes influencing tissue repartitioning. Much of the scientific investigation of the interface between the immune system and metabolic function has been conducted within the human medical field to better understand diseases like obesity and cancer ( Lercher et al., 2020) but many of the concepts can be used to inspire research direction to better understand how health and productivity of agricultural animals can be optimized.