PS4-27. N-carbamylglutamate Alters Plasma Amino Acids in Beef Cattle Fed High- or Low-forage Diets.

Abstract N-carbamylglutamate (NCG) has been used as a nutritional additive with potential to modulate nitrogen metabolism and amino acid (AA) synthesis in cattle. The plasma AA profile is a useful tool to assess these metabolic responses. This study aimed to evaluate the effects of NCG supplementation and dietary forage level on the plasma AA profile. Eight rumen-cannulated Tabapuã heifers (350 ± 70 kg BW) were assigned to two simultaneous 4 × 4 Latin squares. Each square was assigned to a forage level defined by forage:concentrate ratios of 80:20 or 20:80, representing high- and low-forage diets, respectively. Within each square, four levels of NCG supplementation (0, 20, 40, and 60 mg/kg BW) were evaluated, totaling eight treatment combinations. Diets were formulated to be isonitrogenous (14% crude protein, DM basis) to meet the requirements of heifers gaining 1.0 kg/d. Heifers were housed in individual pens with ad libitum access to water and were fed twice daily (0800 and 1600 h) allowing for 5% orts. Four 21-d periods were conducted, including 10 d for diet adaptation and 11 d for sampling. On d 20 of each period, blood samples were collected via indwelling catheter at 0600, 1200, 1800, and 0000 h and composited by animal. Plasma AA concentrations were determined using ultra-performance liquid chromatography (UPLC; Acquity UPLC, Waters Corp., Milford, MA) following pre-column derivatization (AccQ-Tag) with photodiode array detection. No interaction between forage level and NCG supplementation was observed for most AA (P > 0.10), except for Glu, Thr, and Phe. Increasing forage level improved plasma Arg, Lys, and Ile concentrations (P < 0.10). NCG supplementation resulted in positive linear effects on plasma AA concentrations, increasing Arg, Pro, Ile, Leu, and Phe concentrations (P < 0.10) and, consequently, total essential amino acid concentrations (P = 0.03). No linear or quadratic effects of NCG supplementation were observed for the remaining AA (P > 0.10), indicating that responses were specific rather than uniform across the plasma AA profile. In conclusion, NCG supplementation promoted positive linear responses in key amino acids, particularly Arg, Ile, Leu, and Phe. These results indicate a targeted effect of NCG on the plasma AA profile, supporting its potential role in modulating protein metabolism and improving nitrogen utilization efficiency in cattle. ACKNOWLEDGEMENTS: This study was supported by FAPEMIG, CNPq, and CAPES. For image description, please refer to the figure legend and surrounding text.