Modulating Effects of Grape Pomace on the Intestinal Antioxidative and Inflammatory Status in Fattening Pigs

Polyphenol-rich plant products are widely used as feed additives for their anti-inflammatory, antioxidant, and antimicrobial properties. The aim of this research is to test the hypothesis that feeding grape pomace (GP) to fattening pigs modulates the intestinal immune and antioxidant response, promotes the morphostructure of the small intestine, and improves growth performance. Fifty Piétrain fattening pigs were randomly divided into five groups, each consisting of 10 pigs. The groups were fed a basal diet with no supplementation (control) or a diet supplemented with 1 gGP/kg (E1), 5 gGP/kg (E2), 10 gGP/kg (E3), or 15 gGP/kg (E4). The doses were selected based on preliminary tests. The pigs were slaughtered after 90 days, and their duodenum, jejunum, ileum, and caecum were sampled. We recommend a dose of 10 gGP/kg because it leads to many beneficial effects, including a significantly increased villous height, intestinal crypt depth, and V/C ratio in the duodenum and jejunum (p < 0.05). It also decreased the expression of pro-inflammatory markers such as IL-1β in the ileum and caecum, TNF-α in multiple intestinal segments, and MHC-II in the duodenum, jejunum, and caecum. Additionally, antioxidant activity was promoted through the increased immunohistochemical expression of Nrf2 and reduced NF-kB p65 expression. Growth performance also improved, with significantly higher ADG (p = 0.01) and ADFI values (p < 0.01) than those in the control group. In conclusion, polyphenol-rich grape pomace can be used as a supplement in fattening pig diets to maintain their health and productive performance.