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 lactose-negative 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.

The dynamic microbiota in chickens can be affected by exposure to antibiotics, which may alter the composition and substrate availability of functional pathways. Here, 120 Jing Hong chicks at 30 days of age were randomly divided into four treatments totaling seven experimental groups: control chicks not exposed to antibiotics; and chicks exposed to enrofloxacin, diclazuril, and their mixture at 1:1 for 14 days and then not exposed for a withdrawal period of 15 days. Fecal samples were collected from the 7 groups at 8 time-points (exposure to 4 antibiotics and 4 withdrawal periods) to perform in-depth 16S rRNA sequencing of the gut microbiota. Taxon-independent analysis showed that the groups had significantly distinct microbial compositions (p < 0.01). Based on the microbial composition, as compared with the control group, the abundances of the phyla Firmicutes, Actinobacteria, Thermi, and Verrucomicrobia, as well as the families Lactobacillus, Lactococcus, S24-7, and Corynebacterium, were decreased in the antibiotic-exposed chicks (p < 0.01). Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) analyses revealed significant differences in microbiota metabolite pathways due to the genera of the antibiotic-responsive microbes (p < 0.01), especially the pathways relating to cell growth and death, immune system diseases, carbohydrate metabolism, and nucleotide metabolism. Oral treatment with enrofloxacin, diclazuril, and their mixture modified the gut microbiota composition and the microbial metabolic profiles in chickens, with persistent effects (during the withdrawal period) that prevented the return to the original community and led to the formation of a new community.