Impact of Reduced Dietary Crude Protein and Propionic Acid Preservation on Intestinal Health and Growth Performance in Post-Weaned Pigs

This study investigated whether organic acid (OA)-preserved grain could mitigate the negative effects of low crude protein (CP) diets on growth performance, intestinal health, and the coefficient of total tract digestibility (CATTD) of nutrients in weaned piglets. The grain was either conventionally dried or preserved post-harvest with 4 kg of OA per tonne. Ninety-six piglets (28 days old) were assigned to one of four diets in a 2 × 2 factorial design: (1) dried standard CP diet, (2) OA-preserved standard CP diet, (3) dried low CP diet, and (4) OA-preserved low CP diet. Standard and low CP diets contained 20% and 19% CP during the first 15 days, reduced to 19% and 17% CP from days 15–35 post-weaning. Faecal scores (FS) were assessed twice a day while microbial composition, inflammatory markers, colonic volatile fatty acid concentrations, and intestinal morphology were measured on the 8th day post-weaning. Performance metrics were measured over the 35-day experimental period. Low CP diets consistently reduced FS (<i>p </i>< 0.05) and increased colonic molar butyrate proportions (<i>p </i>< 0.01) but increased duodenal <i>IL1B</i> expression compared to standard CP diets (<i>p </i>< 0.05). The OA-preserved grain enhanced beneficial microbial populations (<i>Lactobacillus</i>, <i>Roseburia</i>) while lowering pro-inflammatory cytokines (<i>IL1A</i>,<i> IL17</i>) (<i>p </i>< 0.05). While dried grain with low CP diets reduced average daily gain (ADG), colonic short-chain fatty acids (SCFA) concentrations, and nitrogen digestibility, OA-preserved grain with low CP maintained these parameters and improved final body weight (<i>p </i>< 0.05). Overall, OA-preserved grain mitigated the performance decline associated with low CP diets by enhancing gut health and nutrient digestibility and reducing inflammation, thus presenting a promising alternative nutritional strategy for post-weaned piglets.