Effects of replacing extruded soybean meal with Periplaneta americana residue on laying performance, egg quality, and ovarian function in Guangxi Yao chickens

To reduce dietary reliance on soybean meal and expand alternative protein resources for layers, this study evaluated the effects of replacing extruded soybean meal with PAR on laying performance, egg quality, and ovarian function in Guangxi Yao chickens. A total of 210 30-day-old Guangxi Yao chickens were randomly assigned to six dietary treatments: a control diet (0% PAR) and diets in which extruded soybean meal was replaced with PAR at 10%, 20%, 30%, 40%, or 50% (5 replicates per treatment; 7 birds per replicate) for 24 weeks. Laying performance and egg quality traits were measured; ovarian and serum hormone concentrations and serum immunoglobulins were determined. Ovarian histology was examined, and ovarian transcriptome sequencing was performed with RT-qPCR validation of selected genes.PAR significantly affected average egg weight (P < 0.05), with the highest value observed at 10% replacement. Average daily feed intake showed significant linear and quadratic responses to increasing replacement levels (P < 0.05), whereas laying rate and feed-to-egg ratio did not differ among groups (P > 0.05). For egg quality, the egg shape index was significantly influenced by PAR (P < 0.05) and was lowest at 20% replacement; the remaining egg quality indices generally tended to be improved relative to the control. Regarding hormones, ovarian estradiol was highest at 40% replacement (P < 0.05). In serum, luteinizing hormone increased at 40% replacement, follicle-stimulating hormone was higher at 20% and 30% replacement, and anti-Mullerian hormone was higher at 10% and 50% replacement (P < 0.05); serum progesterone exhibited a significant quadratic effect (P < 0.05). Immunoglobulins (IgA, IgY, and IgM) increased significantly with replacement level and peaked at 50% replacement (P < 0.05). Histological evaluation indicated relatively stable follicular structures at 0-30% replacement, whereas 40-50% replacement was more frequently associated with stromal densification and shrinkage/separation of follicular contents. Transcriptomic analysis showed that differentially expressed genes were mainly enriched in lipid metabolism/PPAR signaling, immune-related processes, ECM-receptor interaction, and oxidative stress pathways. WGCNA identified a module significantly associated with eggshell thickness enriched in MAPK, Wnt, and Hedgehog pathways. RT-qPCR agreed well with RNA-seq trends (r = 0.62, p = 1.93 x 10^-5).Overall, PAR at appropriate levels (particularly 10-30%) can partially improve egg quality and immune indices without compromising laying performance, whereas higher replacement levels may be accompanied by ovarian morphological alterations.