Original link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9952412/
Materials and Methods
A total of 320 male Cherry Valley ducks (1 day old) were obtained from a commercial hatchery and housed in experimental facilities with a controlled-temperature room. The ducks were randomly distributed to 4 treatments with 8 replicates, each containing 10 birds. Each replicate was housed in a 2 m × 2 m pen equipped with two water channels and one tubular feeder. Food and water were provided ad libitum throughout the 42 days of the experimental period. The nutrient values of the basal diets met the nutrients requirements of ducks as required by Nutrient Requirements of Poultry (NRC) . This experiment was conducted in two stages: the early stage (1–21 days) and the middle–last stage (22–42 days). The experimental treatments were composed of the CON group (basal diet), ANT group (basal diet + 50 mg/kg chlortetracycline), HEO group (basal diet + EO 1000 mg/kg) and LEO group (basal diet + EO 500 mg/kg).
The essential oils (product name: Anti-Clos) in the study were supplied by CALID Biotechnology Co., LTD (Wuhan, China). The main active components of the essential oils coated with glycerol monolaurate are glycerol monolaurate (800 g/kg), cinnamaldehyde (54 g/kg) and thymol (6 g/kg). All ducks were treated humanely according to the animal care and ethics committee of the Jiangsu Academy of Agricultural Sciences (SYXK2020-0023), and all efforts were made to minimize animal suffering.
Results
Growth Performance
Compared with the basal diet and antibiotic diet, 1000 mg/kg of EO (HEO group) increased the ADFI, ADG, and BW during 1–42 d (p < 0.05).
Serum Biochemical Indexes
The serum concentration of AST reduced in the LEO (p > 0.05) and HEO (p < 0.05) groups on day 42 compared with the CON group.
Antioxidation of Ileal Mucosa
As shown in Figure 1, no treatment differences were detected in the activity of SOD, MPO, and GSH-PX on day 42 in the ileal mucosa (p > 0.05). However, the activity of MPO was enhanced in both the EO1000 and EO500 groups (p > 0.05), and the higher concentration of EO was associated with higher MPO activity.
Duodenal and Jejunal Morphology
Compared with the CON group, dietary supplementation of EO increased the villus heights (p < 0.01) and the ratio of villus height to crypt depth (c/v) (p < 0.01) in the duodenum and jejunum (Figure 2), but had no significant effects on the crypt depth in the duodenum and jejunum (p > 0.05), while dietary supplementation of chlortetracycline did not affect the duodenal and jejunal morphology (p > 0.05).
Effects of EO on the Gene Expression of Barrier Functional Proteins
The gene expressions of intestinal barrier function proteins are shown in Figure 3. Compared with the basal diet group (CON group), adding different levels of EO increased the mRNA expression of Claudin1 and Occludin in the jejunal mucosa. When the added amount of EO reached 500 mg/kg (LEO group), the gene level of Claudin1 significantly improved (p < 0.01). Supplementation with 1000 mg/kg of EO (HEO group) significantly enhanced the gene expression of Occludin (p < 0.05). In addition, there were no treatment differences in the gene expression of ZO-1 (p > 0.05).
Variation in Alpha and Beta Diversity
The coverage indices were 0.999 or 0.998 in the four groups, indicating that the sequencing depth of each sample was sufficient. The observed, Chao1, ACE, and Shannon indexes all increased, and the Simpson index decreased in the HEO and LEO groups compared to the CON and ANT groups; moreover, the Shannon index increased significantly in the HEO group (p < 0.05) (Figure 4A). α diversity shows that the HEO group (EO1000) has improved diversity and abundance of the gut microflora. To analyze the inter-individual differences, principal co-ordinates analysis (PCoA) and partial least squares discriminant analysis (PSL-DA) (Figure 4C) were used. The PCoA based on the Jaccard index showed distinct separations between the relative abundance of microbial community from the four groups, but the microbial composition was similar within groups. Moreover, PLS-DA further determined the differences in the compositions of gut microbiota between the four groups.
Common and Unique Microbial Populations
Compared to the CON group, the abundance of the families Bacteroides, Desulfovibrio, Phascolarctobacterium, Acetanaerobacterium, Butyricimonas, Anaerobiospirillum, Alistipes, and Ruminococcus2 were increased in the HEO and LEO groups (p < 0.05 or p < 0.01 or p < 0.001). Conversely, Romboutsia, Akkermansia, and Subdoligranulum were visibly reduced when EOs were used as feed additives for ducks.
Conclusions
In conclusion, the present study demonstrated that dietary supplementation of encapsulated EOs at 500mg/kg and 1000 mg/kg improved growth performance, favorably affected gut morphology, and enhanced the gene expression of intestinal barrier function proteins in meat-type ducks. It is noteworthy that dietary EOs at 1000 mg/kg could significantly decrease the FCR of ducks. Furthermore, feeding the ducks with the EO diet significantly changed the composition of bacterial flora and enhanced the potential function of the cecal microbiota. Overall, supplementing duck diets with encapsulated EOs could be a beneficial approach to ensure optimal growth and gut health, both in terms of gut morphology and gut microbiology.
