Dietary inclusion level effects of a phytogenic characterised by menthol and anethole on broiler growth performance, biochemical parameters including total antioxidant capacity and gene expression of immune-related biomarkers

The supplementation of a phytogenic feed additive (PFA) characterised by menthol and anethole was evaluated at three levels on broiler growth performance, nutrient digestibility, biochemical parameters, total antioxidant capacity of plasma, breast and thigh meat as well as on the relative gene expression of immune-related biomarkers. A total of 225 1-day-old male Cobb-500 were assigned into three treatments with five replicates of 15 chicks each. Wheat-soybean meal basal diets were formulated according to a three-phase (i.e. starter, grower and finisher) feeding program. Dietary treatments were: no PFA, PFA at 100 mg/kg diet and PFA at 150 mg/kg diet. Feed and water were available ad libitum. Performance parameters were monitored weekly and all other biological responses were determined at 42 days of broiler age. Increasing PFA level increased (P = 0.044) bodyweight gain at finisher period, decreased quadratically (P = 0.035) overall feed intake, and quadratically improved (P = 0.024) overall feed conversion ratio. Moreover, increasing PFA level increased plasma total antioxidant capacity linearly (P = 0.001) whereas linearly decreased (P = 0.005) triglyceride concentration. Thigh meat cholesterol decreased linearly (P = 0.016) with increasing PFA level. Expression of pro-inflammatory cytokine IL-2 in caecal tonsils increased quadratically (P = 0.046) with increasing PFA level. In conclusion, PFA inclusion at 100 mg/kg diet affected positively performance whereas a stronger improvement mainly in plasma total antioxidant capacity and triglyceride as well as in meat cholesterol was noted for the 150 mg/kg diet level. Inclusion of PFA resulted in increasing pro-inflammatory biomarker IL-2 at local caecal level.