Effects of phytogenic inclusion level on broiler carcass yield, meat antioxidant capacity, availability of dietary energy, and expression of intestinal genes relevant for nutrient absorptive and cell growth–protein synthesis metabolic functions Konstantinos C. Mountzouris A,B , Vasileios Paraskeuas A , Eirini Griela A , George Papadomichelakis A and Konstantinos Fegeros A A Department of Nutritional Physiology and Feeding, Agricultural University of Athens, Iera Odos 75, Athens 11855, Greece. B Corresponding author. Email: kmountzouris@aua.gr Abstract Context. Phytogenic applications in animal nutrition currently attract worldwide scientific attention for their potential to contribute positively to sustainable and high-quality animal production. However, further understanding and substantiation of dietary phytogenic functions is required. Aims. The inclusion level of a phytogenic premix (PP) comprising functional flavouring substances from ginger, lemon balm, oregano and thyme was studied for its effects on broiler growth performance, carcass traits, nutrient digestibility, liver and meat total antioxidant capacity (TAC), and lipid oxidation. The expression of genes for nutrient transporter proteins (SGLT1, GLUT2, PEPT1, BOAT and LAT1), for FABP2 involved in cellular fatty acid uptake and metabolism, and for the mTORC1 complex relevant for protein synthesis were profiled along the intestine. Methods. One-day-old Cobb broiler chickens (n = 500) were assigned to four treatments with five replicates of 25 chickens each. Starter (1–10 days), grower (11–22 days) and finisher (23–42 days) basal diets were supplemented with four levels of PP inclusion as treatments: 0, 750, 1000 and 2000 mg/kg diet, termed control, PP750, PP1000 and PP2000. Feed and water were available ad libitum. Data were analysed by ANOVA, taking the treatment as fixed effect. Statistically significant (P  0.05) effects were further analysed and means were compared using Tukey’s HSD test. Polynomial contrasts tested the linear and quadratic effect of PP inclusion levels. Key results. Growth performance responses were not improved significantly (P > 0.05) by PP inclusion level. However, carcass (P = 0.030) and breast meat yield (P = 0.023) were higher in PP1000 than in the control. In addition, PP1000 had higher (P = 0.049) apparent metabolisable energy than PP2000 and the control. Increasing PP inclusion level increased breast (P = 0.005), thigh (P = 0.002) and liver (P = 0.040) TAC. Breast and thigh meat TAC reached a plateau at PP1000, whereas liver TAC continued to increase linearly. Lipid oxidation in breast meat and liver was delayed linearly (P  0.05) with increasing PP inclusion level. Expression of genes SGLT1, GLUT2, PEPT1, BOAT and FABP2 were not affected by PP inclusion. However, PP inclusion affected the expression of LAT1 (P < 0.001) in jejunum and of mTORC1 in duodenum (P = 0.010) and ceca (P = 0.025). In particular, expression increased with increasing PP inclusion level in a linear and quadratic pattern depending on the intestinal segment. Conclusions. Overall, PP inclusion at 1000 mg/kg diet improved carcass and breast yield, dietary available energy, and overall meat and liver TAC. Preliminary evidence was highlighted for effects of PP in promoting expression of genes relevant for muscle protein synthesis. Implications. This study has contributed new information on effects of a phytogenic premix on broiler meat yield and antioxidant capacity, digestibility, absorption and metabolic functions, further supporting phytogenic benefits for broiler production. Additional keywords: essential oils, gut, meat quality, poultry. Received 14 November 2018, accepted 4 May 2019, published online 30 October 2019 Introduction In principle, phytogenics, having a plant-based origin, are accepted worldwide by the majority of animal husbandry stakeholders, and in many cases they are considered as alternatives to antibiotics in animal diets. Nutritional applications of phytogenic feed additives in broilers are primarily researched for their efficacy to improve zootechnical performance (Mountzouris et al. 2011; Bravo CSIRO PUBLISHING Animal Production Science, 2020, 60, 242–253 https://doi.org/10.1071/AN18700 Journal compilation Ó CSIRO 2020 www.publish.csiro.au/journals/an