Mild synergistic effects of a dietary source of polyphenols (Ceratonia siliqua L.) and vitamin E on light lambs’ rumination activity, nutritional status, and gastrointestinal redox-immune markers

• Combining 20% of carob pulp and Vit E in lamb diets stimulates the rumination activity • Dietary inclusion of carob pulp and Vit E down-regulates jejunal expression of IFN-γ • Including 20% of carob pulp in lamb diets is feasible without harming animal performance • Carob pulp modulates the immune response in the gastrointestinal tract • Vitamin E improves lamb growth and enhances the redox balance This study aimed to evaluate the effect of dietary inclusion of carob pulp (0 vs . 20% Cp, Ceratonia siliqua L.) and vitamin E (Vit E, 40 vs . 300 IU /kg of concentrate) on growth performance, time-budget and eating behaviour, blood metabolites, gastrointestinal and immune markers of fattening light lambs. Seventy-two weaned lambs (females and entire males) were randomly allocated in 12 group pens (6 animals/pen) in a 2 × 2 nutritional factorial design. Growth performance was evaluated, and blood samples were collected twice, whereas behaviour and eating pattern were recorded three times in the fattening period. Gene expression was evaluated by collecting ruminal, jejunal and ileal tissue samples at slaughter. The Cp inclusion did not affect lambs’ performance, but the High Vit E improved the lambs’ growth. Likewise, both Cp and High Vit E independently increased the haematocrit value while only High Vit E improved the plasma α-tocopherol concentration and decreased the ratio MDA:α-tocopherol, considered a proxy of enhanced redox balance. Providing simultaneously 20% of Cp and High Vit E boosted rumination activity. Dietary Cp modified the eating pattern which was slightly delayed to the early afternoon, and decreased blood lactate. In the jejunum, High Vit E and 20%-Cp diets down-regulated IFN-γ expression, while High Vit E down-regulated TNF-α expression. In the ileum, Cp decreased the expression of GPX2, whereas High Vit E down-regulated TGF-β and up-regulated CAT expression. Mild synergistic effects of dietary Cp and Vit E were evident on the nutritional status and gastrointestinal redox-immune markers of concentrate-fed lambs.