PS4-22. Metabolomic Profiling of Serum in Nellore Bulls Supplemented with Guanidinoacetic Acid During the Finishing Phase.

Guanidinoacetic acid (GAA) is the natural precursor of creatine and, as a feed additive, plays a key role in muscle energy metabolism, with positive effects on performance reported in other livestock species. The objective of this study was to evaluate blood metabolic changes induced by GAA supplementation during the finishing phase using a metabolomic approach. The experimental finishing period lasted 74 days. During this phase, 51 Nellore bulls (initial body weight [BW] 500.5 ± 38 kg; age 18 ± 2 months) were blocked by BW (heavy, medium, and light) and placed to three collective pens. Animals were then assigned to one of four treatments: CON (no GAA supplementation; n = 13), GAA3 (0.3 g·kg-1 of dry matter [DM]; n = 13), GAA6 (0.6 g·kg-1 of DM; n = 12), and GAA9 (0.9 g·kg-1 of DM; n = 13). At the end of the finishing phase, animals were slaughtered and blood samples were collected during exsanguination for metabolomic analysis. Blood samples were centrifuged, and the obtained serum was filtered using 3 kDa ultrafiltration filters at 10,000 g for 30 minutes at 4 °C. The supernatant was collected and stored at − 80 °C until analysis by nuclear magnetic resonance (¹H-NMR). Univariate statistical analyses were performed independently for each metabolite using linear models to evaluate treatment effects in an exploratory approach. Pairwise comparisons were conducted between CON and each supplemented group (CON × GAA3, CON × GAA6, and CON × GAA9). During the finishing period, the ¹H-NMR analysis identified 44 metabolites common to all experimental groups. In the comparison between CON and GAA3, lysine (P = 0.006) and mannose (P = 0.016) showed greater concentrations in the supplemented group. In addition, choline (P = 0.093), creatine (P = 0.061), guanidinoacetate (P = 0.095), proline (P = 0.087), and 2-hydroxybutyrate (P = 0.086) showed increasing trends in the GAA3 group. In the comparison between CON and GAA6, serine showed a significant increase in the supplemented group (P = 0.009), whereas taurine showed a tendency toward greater concentration with GAA supplementation (P = 0.055). Finally, in the comparison between CON and GAA9, tyrosine showed a tendency toward higher concentration in the control group (P = 0.094). This study indicated that guanidinoacetic acid supplementation during the feedlot finishing phase may influence protein and energy metabolic pathways in Nellore bulls, as evidenced by circulating metabolites profiles.