Dynamic Changes in Postprandial Plasma Free Amino Acid Levels of the Hepatic Portal, Hepatic, and Jugular Veins in the Healthy Pre-Ruminant Calves

Sufficient amino acids (AAs) supply is crucial in growing animals to maintain the rapid skeletal muscle protein synthesis and healthy growth. Liver is known to be the major organ that plays a central role in AA metabolism. Seeing as few studies have been made to investigate the dynamic changes of postprandial AAs over a short time interval before and after the liver, a first attempt was made to investigate the changes in postprandial free AA levels over eight time points with short interval in plasma, collected simultaneously from the hepatic portal, hepatic, and jugular veins, to better understand the intrahepatic, pre- and post-hepatic AA metabolisms. AAs absorption and uptake by liver occurred soon after feeding and most of the AAs peaked at 30 min postprandial. Two postprandial peaks of the plasma total free AAs, essential AAs (EAAs), and non-essential AAs were observed in hepatic portal and hepatic veins, indicating that two phases of digestion and absorption of AAs may occur in the gastrointestinal tract of the pre-ruminant calves. Individual free AAs showed three main AA transition profiles over time. The total EAA concentration at 240 min postprandial was significantly higher (p < 0.05) in the HPV than in the JV.