Review: Nutrition-based perinatal strategies towards antimicrobial-free systems in piglets

The use of antimicrobials in pig production keeps increasing with the global demand for pork, causing a potential increase in the circulating pool of antimicrobial-resistant genes and other environmental issues. However, developing antimicrobial-free systems is challenging due to a negative impact on welfare and productivity losses. Current alternatives based on feed additives have shown limited success. Piglet gastrointestinal tract health is critical at early stages and depends on the rapid establishment of a balanced microbiota, influenced by sow-derived faecal transfers. The fasting associated with weaning disrupts gut health and the microbiome-host balance, leading to variable growth rates. Tailored feeding programmes involving high-quality and palatable feed ingredients can improve growth, particularly in slow growers at weaning. This review explores three novel nutritional strategies to enhance postweaning piglet performance and welfare. The first strategy leverages prenatal programming to mitigate postweaning anorexia. The programming relies partly on sensory cues triggered by volatile organic compounds (VOCs). These VOCs originate in feed ingredients present in maternal diets that reach the foetus during development. Several feed ingredients commonly used in piglet diets are not used in sow diets, resulting in a distinctive fingerprint of VOCs. Key volatiles (e.g., hexanal, pentanol, α-pinene…) transfer from maternal diets to amniotic and other maternal fluids, influencing postnatal piglet preferences. The concept of "iso-sensorial diets" refers to two feeds formulated to meet different nutrient requirements (e.g., gestating and postweaning diets) while maintaining a continuity in primary olfactory profiles (i.e., VOCs) to encourage feed acceptance. The second strategy focuses on fostering the immature digestive system of weanling piglets, which produces limited endogenous enzymes. Milled grains used in pig diets contain starch and proteins embedded in fibrous cell walls, which restrict enzymatic digestion. This issue can be addressed by optimising particle size (grinding) and supplementing with exogenous enzymes. Larger grain particles have slower starch digestion due to a limiting diffusion rate of α-amylase. Resistant starch is the fraction of dietary starch that resists digestion in the small intestine, exerting a prebiotic effect on the large intestinal microbiota. Non-starch polysaccharides in cell walls also have prebiotic effects supporting beneficial microbes. The third strategy explores the "aminobiotic" effect, where specific amino acids selectively promote beneficial bacteria while inhibiting pathogens, contributing to a healthier gut microbiota. These approaches collectively have the potential to balance nutrient provision with gut health and microbiome robustness, supporting piglet performance and welfare in antimicrobial-free production systems.