Impact of a microencapsulated Enterococcus faecium-phytogenic complex as an antibiotic alternative on growth performance, intestinal morphology, nutrient digestibility, antioxidant status and immune response in broilers

This study evaluated the effects of a microencapsulated Enterococcus faecium-phytogenic complex (Thyme, Oregano, Ajwain, and Enterococcus faecium; TOA-EF) on 360 Ross 308 male broilers. Birds were randomly assigned to four treatments (6 replicates of 15 birds): a basal diet (NC), basal + Bacitracin (PC), and the basal diet supplemented with 0.75 or 1.5 g/kg of TOA-EF. Our results showed that while body weight gain remained unaffected (ANOVA-P > 0.05), both TOA-EF supplementation and the PC treatment significantly reduced feed intake compared with the NC group (ANOVA-P < 0.001), following a significant linear trend (P = 0.009). The feed conversion ratio was significantly improved (ANOVA-P = 0.002) in TOA-EF birds compared to the NC group, with the lowest FCR observed in the 0.75 g/kg TOA-EF group (1.59) and followed by the 1.5 g/kg TOA-EF (1.61), versus 1.70 in the NC group; however, the PC group did not differ significantly from the NC. While crypt depth and villus width remained unaffected (ANOVA-P > 0.05), TOA-EF supplementation significantly affected jejunal morphology, exhibiting a linear (P = 0.025) and quadratic (P = 0.028) increase in villus height (ANOVA-P = 0.034). The villus height to crypt depth ratio showed significant linear (P = 0.016) and quadratic (P = 0.021) responses, although the overall treatment effect was not significant (ANOVA-P = 0.062). Villus surface area showed a significant linear response to TOA-EF supplementation (ANOVA-P = 0.039, Linear-P = 0.043). Ileal digestibility of dry matter, ash, calcium, and phosphorus remained unaffected by dietary treatment (ANOVA-P > 0.05). Ileal CP digestibility differed significantly among dietary treatments (ANOVA-P = 0.001), with significant linear (P = 0.013) and quadratic (P < 0.0001) responses to TOA-EF supplementation. The highest mean CP digestibility (79.0%) was observed in the 1.5 g/kg group. Total antioxidant capacity, superoxide dismutase and glutathione peroxidase activities, and antibody titers against Newcastle disease virus remained unaffected (ANOVA-P > 0.05). The overall treatment effect on serum malondialdehyde concentrations was not significant (ANOVA-P = 0.236), although a significant linear response was detected (P = 0.045). Overall, TOA-EF supplementation influenced feed efficiency and selected aspects of intestinal morphology and protein digestibility, without affecting body weight gain and this blend may have potential as an alternative to antibiotic growth promoters in broiler diets.