Effects of dietary paddy rice on the growth, serum biochemistry, intestinal development, microbiota, and metabolism of young laying ducks in a rice–duck–crayfish farming system

This study investigated the effects of feeding paddy rice on the physiology, metabolism, and gut microbiota of ducks in a rice-duck-crayfish (RDC) system. A total of 540 ducks (20-days-old) were randomly divided into 3 groups with 3 replicates and 60 ducks per replicate. The 40-d experiment involved 3 diet treatments: a complete diet (CD), 50% paddy rice + 50% complete diet (RCD), and 100% paddy rice diet (RD). Results show that feeding paddy rice did not significantly affect duck growth, the final weight in the RD group was reduced by 5%, and the feed-to-gain ratio increased by 7% compared to the CD group. Additionally, compared with the CD group, the keel length, gizzard and proventriculus indices, and serum high-density lipoprotein levels increased (P < 0.05), and duodenal villus height and ileal crypt depth (P < 0.05) reduced in the RD group and ileal villus height decreased in the RCD group (P < 0.05). Compared with the CD group, the cecal abundance of Bacteroidota, Prevotellaceae_Ga6A1_group, and Prevotellaceae_NK3B31_group decreased in the RD group (P < 0.05) while the abundance of Firmicutes, Megamonas and Faecalibacterium increased (P < 0.05). Metabolome analysis revealed that serum citric acid increased (P < 0.05) in the RCD and RD groups, whereas cytidine, cytosine, and 4-aminobutyric acid decreased (P < 0.05) in the RD group. In conclusion, these preliminary results suggest that paddy rice supplementation under an RDC system had no significant effect on duck growth, but it did cause changes in intestinal morphology, microbiota, and serum metabolic profiles. However, it is important to note that the limited overall number of replicates in this study contributed to a certain degree of high variance. While the growth differences among groups were not statistically significant, the full replacement of paddy rice still poses potential performance losses. In practical applications, this finding provides a reference for the RDC system, but further validation through larger-scale trials is required.