Assessment of a phytogenic feed additive effect on broiler growth performance, nutrient digestibility and caecal microflora composition

The aim of this work was to evaluate the effect of three inclusion levels of a phytogenic feed additive (PFA) comprising a blend of essential oils from oregano, anise and citrus on broiler growth performance, nutrient digestibility and caecal microflora composition. Five hundred and twenty-five, 1-day-old, male Cobb broilers received a maize–soybean meal basal diet (BD) and depending on the type of addition were allocated in the following five experimental treatments for 6 weeks: BD–no additives (C), BD containing 80mg PFA/kg diet (E1), BD containing 125mg PFA/kg diet (E2), BD containing 250mg PFA/kg diet (E3) and BD containing avilamycin at 2.5mg/kg diet (A). Treatment A was used as a positive control due to the well-known function of avilamycin as an antimicrobial growth promoter in poultry. Overall broiler body weight gain (BWG) increased linearly (P=0.039) with increasing PFA level, however, the avilamycin treatment A did not differ (P≥0.05) from the PFA and C treatments. Overall feed intake (FI) decreased quadratically (P=0.046) with increasing PFA level, while the FI for treatment A did not differ from the rest of the treatments. The overall gain:feed ratio improved linearly (P<0.001) with increasing PFA level and treatment A (0.57) did not differ from E2 (0.58) and E3 (0.58) but it was significantly (P<0.05) better compared to E1 (0.54) and C (0.54). The PFA level had a marginal linear (P=0.059) and a significant (P=0.021) quadratic effect on the total tract apparent digestibility (CTTAD) of organic matter (OM) and the nitrogen corrected apparent metabolisable energy (AMEₙ) of experimental diets, respectively, with treatment E1 having the higher (P<0.05) CTTAD of OM (0.79) and AMEₙ (13.4MJ/kg diet) and treatment A being not different from the four other treatments. On the other hand, the avilamycin treatment A had a significantly (P<0.05) higher coefficient of ileal apparent digestibility (CIAD) of fat (0.70) as well as CTTAD of ash (0.53) and fat (0.77) compared to the PFA treatments and C. There was a linear increase of caecal Lactobacillus (P=0.002), Bifidobacterium (P=0.001) and Gram positive cocci (P=0.007) concentration with increasing PFA level at 42 d old broilers. In addition, caecal coliforms at 14 d old broilers were significantly (P<0.05) lower in treatments E2 and E3 compared with A. In conclusion, this small scale study provides additional evidence that phytogenic efficacy in broilers depends on the feed inclusion level used and the broiler growth period with most of the PFA overall beneficial effects seen mainly in the finisher growth period. Further work is warranted in order to evaluate phytogenic efficacy with different basal diets and under commercial production conditions.