L-Ornithine-L-aspartate enhances growth performance and nitrogen metabolism via modulation of intestinal amino acid transporters and microbiota in broilers.

Abstract

L-Ornithine-L-aspartate (OA) is a stable salt formed by the ionic bonding of ornithine and aspartic acid. While OA is known to regulate nitrogen metabolism and ammonia (NH 3 ) detoxification more effectively than its individual components in clinical settings, their specific effects and mechanisms in broiler chickens remain unexplored. Crucially, it is unknown whether OA exerts superior biological effects compared to a physical mixture of ornithine and aspartic acid in broiler chickens. Therefore, this study selected white-feathered broilers to investigate the comparative effects of dietary supplementation with OA versus a mixture of ornithine and aspartic acid on growth performance, nitrogen metabolism, and intestinal health. The objective of this study was to elucidate the mechanisms underlying the potential superiority of the salt form (OA) over the mixture. Compared to the basal diet, both supplementation groups improved growth performance and slaughter performance by promoting glutamine (Gln) synthesis and NH 3 detoxification, thereby enhancing protein deposition. Specifically, supplementation significantly reduced the feed conversion ratio from d 1 to 21 and increased body weight and breast muscle percentage at d 42 (P < 0.05). Notably, OA demonstrated superior efficacy compared to the mixture. Mechanistically, OA significantly increased hepatic ornithine aminotransferase (OAT) activity at d 21, facilitating ornithine transamination for Gln synthesis. In the gut, OA uniquely reduced duodenal crypt depth (CD) and up-regulated the mRNA expression of key amino acid (AA) transporters (SLC1A5, SLC25A15, and SLC38A2) in the jejunum, leading to significantly higher apparent ileal digestibility of AAs (P < 0.05). Metabolomic and microbiomic analyses revealed that, compared to the mixture, OA significantly modulated arginine biosynthesis pathways (gga00220) and down-regulated L-ornithine (C00077) abundance in ileal chyme. Furthermore, OA improved the cecal microbiota by increasing the relative abundance of butyrate-producing Agathobaculum, reducing pathogenic Escherichia, and up-regulating energy metabolism pathways. In summary, while both forms are beneficial, OA is superior to the physical mixture of ornithine and aspartic acid in improving broiler performance. This advantage of the OA was correlated with the up-regulated intestinal AA transporters, improved the digestibility of nutrients such as ornithine, and the modulated gut microbiota towards a butyrate-producing profile, coupled with increased hepatic OAT activity.