Peppermint extract alters egg production and quality, antioxidant capacity and colonic microbiota of laying hens during late laying period

Peppermint contains substantial bioactive ingredients belonging to phytoestrogen, and its effects on the production of late laying hens deserve more attention. This study determined the effects of dietary supplementation with peppermint extract (PE) on egg production and quality, yolk fatty acid composition, antioxidant capacity, and colonic microbiota of late laying hens. A total of 216 healthy 60-week-old black feather laying hens were randomly divided into four groups (nine replicates per group, six hens per replicate) and fed a basal diet (control group, CON) or basal diets added with 0.1%, 0.2%, and 0.4% PE (LPE, MPE and HPE groups) for 28 days. Results showed that, compared to CON group, dietary PE supplementation increased the laying rate, serum triglyceride, immunoglobulin G levels, and total antioxidant capacity, but decreased the yolk color (P < 0.05); MPE and HPE supplementation increased eggshell thickness, serum total protein level, and superoxide dismutase activity (P < 0.05). Meanwhile, obvious increase in the yolk contents of C14:0, C18:3n3, C18:3n6, C23:0, C24:0, and C24:1n9 were observed as dietary PE addition (P < 0.05). The saturated fatty acid content in egg yolk was higher (P < 0.05) in the MPE and HPE groups than CON and LPE groups. The relative abundance of colonic Proteobacteria was decreased (P < 0.05) in PE supplementation diets. HPE addition increased the colonic richness of gram-positive bacteria and decreased the richness of gram-negative and potential pathogenic bacteria compared to LPE group (P < 0.05). Microbial functions prediction analysis indicated that the colonic microflora of PE group was mainly enriched in the KEGG pathways of fatty acid degradation, fatty acid metabolism, amino sugar and nucleotide sugar metabolism, and so on. Regression analysis revealed that the optimal PE supplemental level for egg production and quality, antioxidant capacity, and yolk fatty acid of laying hens during late laying period was 0.28% to 0.66%. In summary, dietary PE supplementation improved egg production and quality (including yolk fatty acid composition) by increasing serum IgG and antioxidant capacity and shaping intestinal microbiota in late-phase laying hens.