The effects of condensed tannins in sula (Hedysarum coronarium) on valine kinetics in the ovine mammary gland

Abstract

We tested the hypothesis that condensed tannins (CT) in Sulla (Hedysarum coronarium) increase the partitioning of essential amino acid (EAA) to the mammary gland in late lactating ewes. Lactating ewes (12) were surgically prepared with permanent indwelling arterio-venous catheters across the mammary gland, a cannula in the abomasum and a transonic flow probe fitted around the pudic artery at 1 week postpartum. All ewes were fed on fresh Sulla until the completion of the experiment. Two weeks after surgery (week 3 of lactation), half the ewes were orally drenched (4 times per day) with polyethylene glycol to remove the effects of the CT (PEG), whilst the remaining ewes (Control) received a drench of water according to a block design. At week 6 of lactation, a primed continuous infusion of [1-¹³C]-valine into the abomasum was used to quantify the kinetics of valine across the mammary gland, using a 2- or 3-compartment model. Blood was obtained by consecutive 2-h continuous blood sampling (6-12 h from the start of infusion) from the mesenteric artery and caudal superficial epigastric vein, to measure the isotopic enrichment and concentration of valine in plasma. Mammary blood flow tended to decrease (P<0.10) with PEG, and this resulted in a reduction in the flow of valine to the mammary gland. The net flux of valine across the mammary gland was not affected (P<0.10). Transmembrane valine transport into and out of the mammary intracellular pool was higher (P<0.05) in the control group compared with the PEG group. Irreversible loss rate (ILR) of valine, calculated using a 2-compartment kinetic model, tended to be lower (P=0.10) in the PEG group while the ILR estimated from a 3-compartment model was not affected (P>0.10). The rate of valine released from protein degradation was not affected (P>0.10) by treatments. These results suggest that the CT in Sulla increased mammary blood flow, supplying more valine (and other EAA), for mammary protein synthesis and/or oxidation.