Effects of N-carbamylglutamate on down yield and quality and thyroid transcriptome in breeding Huoyan geese

The efficiency of goose down production depends on improvements in both yield and quality, and thyroid function plays a critical role in feather growth. Therefore, exploring nutritional strategies to regulate thyroid function for enhancing down traits is of great importance. N-carbamylglutamate (NCG), an amino acid supplement, has been shown to improve livestock and poultry production performance. However, its regulatory mechanism on down traits and thyroid function in Huoyan geese remains unclear. This study aimed to evaluate the effects of dietary NCG supplementation on down production performance in breeding Huoyan geese and to preliminarily elucidate its mechanism using thyroid transcriptome sequencing. A total of 240 two-day-old female Huoyan geese were randomly assigned to a control group (CON) and an NCG group (N), with six replicates per group and 10 geese per replicate. The experimental period lasted 293 days. At 295 days of age, blood, skin, and thyroid samples were collected. Down yield, cluster length, fiber diameter, thyroid index, and T4 concentration were measured, along with histomorphological and transcriptomic analyses. Results showed that the NCG group had significantly higher total down yield, chest cluster length, and 1000-cluster weight (P < 0.05), while fiber diameter was significantly lower (P < 0.05). The S/P ratio in skin follicles was significantly higher in the NCG group (P < 0.05). Thyroid follicle diameter and colloid resorption vacuole count were significantly increased (P < 0.05), while T4 concentration showed no significant change. Thyroid transcriptomic analysis identified 122 upregulated and 1663 downregulated genes. GO annotation highlighted that upregulated genes including CLIC5, WDR64, LMO1, and GPR158 were associated with cytoskeletal organization, transcriptional regulation, and signal transduction, whereas downregulated genes including COX5B and MAF1 were related to ribosome function, energy metabolism, and translation inhibition. KEGG enrichment analysis revealed significant enrichment in the MAPK signaling pathway, glutathione metabolism, and ribosome pathway. In conclusion, dietary 0.06% NCG improves down yield and quality in breeding Huoyan geese by promoting secondary follicle development, improving down structure, and synergistically activating thyroid function.