Effect of feed supplementation with a thymol plus carvacrol mixture, in combination or not with an NSP-degrading enzyme, on productive and physiological parameters of broilers fed on wheat-based diets

The current study was conducted to evaluate the effect of feed supplementation with a phytogenic product (equal mixture of thymol plus carvacrol; T+C) on performance, nutrient retention, volatile fatty acid (VFA) profiles, cecum microbial ecosystem, serum parameters and characteristics of gastrointestinal tract of broilers fed on wheat-based diets with or without an NSP-degrading enzyme product (xylanase plus β-glucanase; E) from d 0 to 42. Six dietary treatments were arranged according to a factorial design with three levels of T+C (0, 100 and 200 mg/kg of diet) and two levels of E (0 and 0.5 g/kg of diet). Each treatment was replicated five times with 12 chicks per replicate. There was no interaction effect between E and T+C on any of the measured parameters. Compared with the control group, birds fed diets containing E or T+C had a higher (P < 0.01) final body weight, average daily gain and feed efficiency at d 42. Digesta viscosity was reduced (P < 0.05) in treatments with E addition in all parts of the small intestine. In treatments with T+C inclusion digesta viscosity was reduced in jejunum and ileum at d 24. E or T+C treated birds showed an increased (P < 0.05) retention of DM, protein and energy. Dietary supplementation with E and T+C increased (P < 0.01) total VFA and acetate levels at d 24 and 42, whereas the level of butyrate decreased (P < 0.01). Escherichia coli and Clostridium perfringens counts were lower (P < 0.01) than controls, and Lactobacilli counts were higher (P < 0.01), in birds fed on diets supplemented with enzyme or T+C at the rate of 200 mg/kg. E supplementation increased (P < 0.05) serum triglyceride, total cholesterol, total protein (TP), albumin and globulin concentrations, while T+C supplementation decreased (P < 0.05) total cholesterol, TP and albumin at d 40. E supplementation decreased (P < 0.01) the relative length of duodenum, jejunum and ileum of broilers. Moreover, carcass, liver and pancreas relative weights decreased (P < 0.05) with E supplementation at d 42. T+C dietary supplementation only affected carcass relative weight and jejunum and ileum relative lengths. The present study showed that thymol + carvacrol, in combination or not with an NSP-degrading enzyme, improved growth performance, enhanced nutrients retention, increased total VFA, reduced cholesterol and modulated intestinal microbial counts in broilers fed on a wheat-based diet.