Branched-chain amino acid and ketoacid supplementation differentially modulate amino acid and ketoacid metabolisms and profiles in fresh cows.

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After calving, dairy cows experience a negative protein and AA balance, potentially impairing milk production and increasing susceptibility to metabolic disorders. The objectives of this study were to quantify circulating concentrations of proteinogenic AA and branched-chain keto acid (BCKA) and characterize mRNA expression of key enzymes regulating branched-chain AA (BCAA) catabolism. Thirty-six multiparous Holstein cows were enrolled in a randomized block design, receiving continuous abomasal infusion for 21 d after parturition. Treatments (12 cows each) were control (CON), cows abomasally infused with 0.9% saline; cows abomasally infused with BCAA (67 g Val, 50 g Leu, and 34 g Ile; BCA); and cows abomasally infused with BCKA (77 g keto Val, 57 g keto Leu, and 39 g keto Ile; BCK). All cows were randomly assigned to treatments after parturition and received the same diet throughout the experimental period. Blood was collected at 0, 3, 7, 14, and 21 d postpartum for quantification of 20 AA with liquid chromatography-tandem MS. Liver was also harvested on 7, 14, and 21 d postpartum for quantification of BCAA catabolism genes. Compared with CON, BCA cows had higher plasma BCAA, keto Leu, and keto Ile (but not keto Val), along with higher plasma EAA and total AA (TAA). Abomasal BCKA infusion increased plasma BCKA, Val, and Ile (but not Leu), and elevated plasma EAA without affecting TAA. The BCK cows had higher overall plasma Met and His. Additionally, at specific time points measured, BCA cows had higher concentrations of Lys and Arg compared with CON cows, whereas BCK cows had higher concentrations of Phe, Met, His, and glutamate compared with CON cows. Compared with CON, BCA cows had greater expression of all BCAA/BCKA catabolism genes for at least one time point measured, whereas BCK cows only exhibited greater expression of Methylcrotonyl-CoA Carboxylase Subunit 1 and Methylmalonyl-CoA Mutase on d 14 compared with CON. Overall, these results suggest that postruminal BCAA and BCKA infusion distinctly modulated AA profile and BCAA/BCKA catabolism in fresh cows, revealing divergent metabolic adaptations. These findings highlight the distinct roles of BCAA and BCKA in nutrient utilization and metabolic function during early lactation. Future work is required to evaluate specific changes in the interrelated metabolism of BCAA and BCKA to clarify their specific contributions to lactation performance and metabolic regulation.