Effects of ruminally protected betaine and choline on net flux of nutrients across the portal-drained viscera and liver of meat goat wethers consuming diets differing in protein concentration

Six Boer × Spanish goat wethers (43 ± 5.1 kg BW) were used in an experiment with a 2 × 3 factorial arrangement of treatments to investigate effects of dietary CP level (9% and 15% DM) and supplementation with ruminally protected betaine or choline (0.9% DM) on plasma concentrations and net fluxes of oxygen, ammonia N, non-esterified fatty acids (NEFA), triacylglycerols (TG) and cholesterol across the portal-drained viscera (PDV) and liver. Neither betaine nor choline affected blood flow, packed cell volume, hemoglobin concentration or oxygen consumption. Blood flow and oxygen consumption were greater (P < 0.05) for 15% versus 9% dietary CP. Arterial plasma ammonia N concentration was greater (P < 0.05) for 9% versus 15% CP. Compared with Control, choline supplementation decreased (P < 0.05) PDV release and hepatic uptake of ammonia N with the 15% CP diet, whereas betaine decreased (P < 0.05) PDV release and hepatic uptake of ammonia N with 9% dietary CP. With 9% dietary CP, the concentration of NEFA in arterial, hepatic venous and portal venous plasma ranked (P < 0.05) choline < Control < betaine; with 15% CP, NEFA concentration also was greater (P < 0.05) for betaine versus Control, although the magnitude of difference was smaller than with 9% CP. The only treatment effect on NEFA net fluxes was greater (P < 0.05) hepatic uptake with 9% CP than with 15%. Plasma TG concentrations also were increased (P < 0.05) by betaine with 9% dietary CP, whereas choline did not have any influence with either dietary CP level. Concentrations and net fluxes of cholesterol were similar among treatments. In conclusion, these data indicate that potential effects of ruminally protected betaine on performance of ruminants might involve changes in lipid metabolism, with the magnitude of alteration varying with dietary CP level.