Nowadays, there is much legislation in the world devoted to restrict the use of synthetic antibiotics in the poultry industry, which
could reduce performance rate and production profits. Various phyto-biotic growth promoters have been proposed to serve as
antibiotic alternatives with emphasis on plant extracts and essential oils. This study was conducted to assess the impacts of using
the oregano essential oil (OEO) (comprised of 5% thymol and 65% carvacrol) and Enviva essential oil (EEO) (4.5% cinnamaldehyde
and 13.5% thymol) as phytobiotic feed additives (PFA) on growth performance, cecal microbiota and serum biochemicals of
growing ducks. In total, 800 11-day-old ducklings, housed in 20 floor pens, were allotted randomly into five dietary treatments: ( i)
A basal diet (BD) (control), ( ii.) BD +50 mg EEO/kg, ( iii.) BD +100 mg EEO/kg, ( iv.) BD +150 mg OEO/kg and (v.) BD +300 mg
OEO/kg diet. The growth performance traits were studied between 11 and 42 days of age. At the experiment end, 40 ducks were
slaughtered (eight/ treatment) and cecal digesta and blood samples were collected to estimate the cecal bacterial populations and
serum blood biochemicals. The results indicated that the tested levels of OEO and EEO did not display any significant effect
( P>0.05) on the duck’s final BW, BW gain, growth rate, feed intake, feed conversion ratio or survivability rate. Besides, the
different levels of EEO and OEO decreased the cecal populations of Coliforms ( P<0.01), total aerobes ( P<0.01) and lactosenegative
Enterobacteria ( P<0.05) in comparison with those of the control group. Finally, the tested EEO and OEO levels did not
show any significant effect on the serum variables; in terms of total protein, albumin, globulin, total cholesterol, triglycerides,
alanine aminotransferase and aspartate aminotransferase. In conclusion, the antimicrobial effect of the OEO and EEO against the
cecal microbiota has been proven, while they did not display significant effects on the growth performance or blood variables of
growing ducks.