Phytogenic administration and reduction of dietary energy and protein levels affects growth performance, nutrient digestibility and antioxidant status of broilers

The aim of this study was to investigate the effect of reduced dietary energy (ME) and protein (CP) levels along with administration of a phytogenic feed additive (PFA) based on oregano, anise and citrus essential oils, on broiler growth performance, nutrient digestibility, meat and blood biochemical parameters and total antioxidant capacity (TAC). Depending on dietary ME and CP level down regulation compared to a corn-soybean meal basal diet A used as positive control, three diet types [A, B(=A-3%) and C(=A-6%)] were implemented. Depending on the inclusion or not of PFA at 125 mg/kg diet, 450 1-d old, male Cobb broilers were randomly allocated in six treatments according to a 3*2 factorial arrangement with 5 replicates of 15 broilers; A: diets formulated optimally to meet broiler nutrient requirements for maximizing protein content of meat for starter, grower and finisher growth periods; APh: A+PFA; B: suboptimal in ME and CP levels by 3%; BPh: B+PFA; C: suboptimal in ME and CP levels by 6%; CPh: C+PFA. Feed conversion ratio (FCR) was improved in birds fed diet A compared to diet C during the grower period (Psub(D)=0.021) and overall (Psub(D)=0.010). Phytogenic supplementation resulted in higher (Psub(D*Ph)=0.020) total tract apparent digestibility of fat in birds fed diet C compared to diet A. Birds fed diet A had higher (Psub(D)=0.001) plasma cholesterol, compared to birds fed diet C. In addition, birds fed diets A and B had higher (Psub(D)=0.002) breast protein content compared to C. Overall, PFA inclusion reduced cholesterol (Psub(Ph)=0.002) and increased plasma TAC (Psub(Ph)<0.001). Moreover, PFA increased breast (Psub(Ph)=0.001) and thigh (Psub(Ph)=0.01) TAC. In conclusion, a reduction in dietary ME and CP levels, adversely affected the FCR, whereas PFA supplementation tended (Psub(Ph)=0.089) to compensate these effects. Moreover, the addition of PFA reduced plasma cholesterol and improved plasma and meat TAC.