Postruminal infusions of amino acids or glucose affect metabolisms of splanchnic, mammary, and other peripheral tissues and drive amino acid use in dairy cows

摘要

Effects of AA and glucose infusions on efficiency ofuse of essential AA (EAA) were studied according toa 2 × 2 factorial using 5 multicatheterized cows in a 4× 4 Latin square plus one cow, with 2-wk periods. Thediet provided 87% of energy and 70% of metabolizableprotein requirements, and the 4 treatments were abomasalinfusions of (1) water, (2) an AA mixture with acasein profile (695 g/d), (3) glucose (1,454 g/d), or (4) acombination of AA and glucose infusions. Milk sampleswere collected on the last 6 milkings. On d 14, 6 bloodsamples were collected from arterial, and portal, hepatic,and mammary venous vessels. Splanchnic plasmaflow was calculated by dilution of p-aminohippurateand mammary flow by the Fick principle using Phe +Tyr. The net flux of AA across tissues [splanchnic, i.e.,portal-drained viscera (PDV) + liver, and mammarygland] was calculated as the efflux minus the influxacross that tissue. The efficiency of EAA was calculatedas the sum of exported true proteins [milk protein yield(MPY), scurf, and metabolic fecal protein] multipliedby their respective AA profile and divided by the predictedAA supply minus AA endogenous urinary loss.In addition, catabolism was estimated for each tissue:AA supply − (portal net flux + metabolic fecal protein)for the PDV; −hepatic net flux for the liver; splanchnicnet flux − (−mammary net flux + scurf) for the otherperipheral tissues; and −mammary net flux − milk forthe mammary gland. The MIXED procedure (SAS InstituteInc., Cary, NC) was used with cow as a randomeffect. No AA × glucose interaction existed for most ofthe measured parameters. With infusions of AA andglucose, MPY increased by 17 and 14%, respectively.The decreased efficiency of EAA-N with AA infusionresulted from increased EAA-N in MPY smaller thanthe increased EAA-N supply and was accompanied byincreased liver catabolism of His + Met + Phe (representinggroup 1 AA) and increased mammary and PDVcatabolisms of group 2 AA-N (Ile, Leu, Lys, and Val).In contrast, the increased efficiency of EAA-N with glucoseinfusion, resulting from increased EAA-N in MPYwith no change in EAA-N supply, was accompanied bydecreased mammary catabolism of group 2 AA-N andhepatic catabolism of His + Met + Phe. No mammarycatabolism of His, Met, and Phe existed in all treatments,as indicated by the mammary uptake to milkoutput ratio close to one for these EAA. Therefore, themammary gland contributes significantly to variationsof efficiency of group 2 AA-N through variations of AAcatabolism, in response to both AA and glucose supplies,whereas additional PDV catabolism was observedwith increased AA supply. Partition of AA use betweentissues allows to delineate their anabolic or catabolicfate across tissues and better understand changes ofefficiency of EAA in response to protein and energysupplies.