Effect of abomasal glucose infusion on splanchnic amino acid metabolism in periparturient dairy cows.
Six Holstein cows fitted with ruminal cannulas and permanent indwelling catheters in the portal vein, hepatic vein, mesenteric vein, and an artery were used to study the effects of abomasal glucose infusion on splanchnic AA metabolism. The experimental design was a split plot, with cow as the whole plot, treatment as the whole-plot factor and days in milk (DIM) as the subplot factor. Cows were assigned to 1 of 2 treatments: control or infusion of 1,500 g/d of glucose into the abomasum from the day of calving to 29 DIM. Cows were sampled prepartum and at 4, 15, and 29 DIM. Postpartum dry matter intake increased at a lower rate with infusion compared with the control. Arterial concentrations of all essential AA (EAA) were lower with infusion compared with the control. Net portal fluxes of His, Ile, Leu, Lys, Met, Phe, Thr, Val, Ala, Pro, Ser, and Tyr were lower with infusion compared with the control and the net portal fluxes of these AA showed positive correlations with dry matter intake, whereas the net portal fluxes of Asp, Glu, and Gln were unaffected by treatment. Net hepatic fluxes of EAA were not affected by treatment but increased as lactation progressed with both treatments. On a net basis, all EAA were removed by the liver prepartum and at 4 DIM, whereas Met, Phe, and Thr were the only EAA being removed at 29 DIM. Except for Ala, AA removed by the liver might be used primarily for noncatabolic processes, as exemplified by the 16% of hepatic Gly uptake accounted for as urinary hippurate. The measured hepatic uptake of glucogenic precursors (glucogenic AA, volatile fatty acids, lactate, and glycerol) accounted for 50 to 90% of the hepatic release of glucose. The hepatic urea output accounted for more than 100% of the hepatic ureagenic precursor uptake, indicating that the glucogenic precursors unaccounted for are nonnitrogen-containing compounds. In conclusion, an increased exogenous glucose supply to the small intestine did not seem to affect the amount of EAA and non-EAA available for peripheral tissues in early lactation, and the study did not indicate an AA-sparing effect of small intestinal glucose absorption. In periparturient dairy cows, hepatic catabolism of AA was not driven by the increased whole-body demand for glucose, and Ala was the only AA that contributed substantially to hepatic gluconeogenesis. In very early lactation, the supply of EAA might be of greater concern than the supply of glucogenic substrates.
Larsen
M
M
Department of Animal Health, Welfare and Nutrition, Faculty of Agricultural Sciences, Aarhus University, DK-8830 Tjele, Denmark.
Kristensen
N B
NB
D000018:Abomasum / Q000378:metabolism*; D000596:Amino Acids / Q000097:blood / Q000378:metabolism*; D000818:Animals; D002417:Cattle / Q000378:metabolism*; D003612:Dairying; D004435:Eating / Q000502:physiology; D005260:Female; D005947:Glucose / Q000008:administration & dosage / Q000378:metabolism*; D008099:Liver / Q000098:blood supply / Q000378:metabolism*; D049590:Postpartum Period; D011247:Pregnancy
D000596:Amino Acids; D005947:Glucose