<i>In vitro</i> effects of saponins, tannins and lipids on rumen fermentation and intestinal health markers in a ruminant weaning context

Dairy ruminants often experience physiological disturbances during the post-weaning, includingsuboptimal rumen fermentation due to an underdeveloped rumen microbiota, and diarrhoeaassociated with intestinal inflammation and oxidative stress. This study explored six commercialfeed additives with a potential dual mode of action to optimise both rumen fermentation andintestinal health in a post-weaning scenario. The experimental treatments included dietary sup-plementation with saponins (SAP), tannins (TAN), lauric acid (LAU), fish oil (FIO), high-unsaturatedolein (HUO) and high-saturated olein (HSO). Additives were tested at four doses (0, 100, 300 and600 mg/L) with four experimental replicates. Effects on rumen fermentation were evaluated inbatch cultures using inocula from dairy lambs and a high concentrate substrate, while intestinalhealth responses were evaluated in Caco-2 cells. Saponins (p ¼ 0.01) and tannins (p < 0.01) lin-early decreased rumen ammonia-N concentration in batch cultures. In Caco-2 cells, saponinsimproved metabolic activity (p ¼ 0.04), whereas tannins reduced pro-inflammatory IL-6 concentra-tion (p < 0.01), suggesting beneficial effects on intestinal health. Lipid sources exerted minimaleffects on rumen fermentation and induced intestinal inflammation when supplemented at highdoses. Overall, the physiological constrains of dairy ruminants during the post-weaning period,such as an immature rumen microbiota, absence of protozoa and low rumen pH, may limit theefficacy of additives in improving rumen fermentation. Nevertheless, saponins and tanninsshowed potential to reduce rumen proteolysis and support intestinal health during this criticaldevelopmental stage. Further in vivo research is required to validate these findings.