Influence of betaine and conjugated linoleic acid on portal-drained viscera flux of metabolites in growing Iberian pigs

Betaine and CLA alter growth and nutrient partitioning in pigs. Betaine can decrease fat deposition and increase carcass lean, whereas CLA can increase ADG, feed efficiency, and protein accretion and decrease body fat. However, the mechanism of action remains unclear. As portal-drained viscera (PDV) are very metabolically active tissues that may compromise nutrient delivery to the periphery, we hypothesize that differences in net PDV flux of metabolites may help to explain some of the effects elicited by betaine and CLA. Sixteen 30 kg BW Iberian barrows were randomly assigned to 4 diets (control supplemented or not with 0.5% betaine, 1% CLA, or 0.5% betaine + 1% CLA) and surgically fitted with 3 chronic indwelling catheters: in the portal vein, the ileal vein, and the carotid artery. When pigs were recovered from surgery, a 15-mL pulse dose of para-aminohippuric acid (PAH; 2% wt/vol) was infused into the ileal vein followed by a continuous infusion of 0.8 mL/min. Blood samples simultaneously were taken from the carotid artery and portal vein every 30 min for 4 h and hourly until 6 h after feeding 1,200 g of the diet and centrifuged, and the plasma was stored at -20 degrees C. Portal blood flow was determined by the PAH dilution method and net flux of metabolites was determined according to the Fick principle. Net PDV flux (mmol/h) of lactate, albumin, creatinine, urea, triglycerides, and cholesterol were no different (P > 0.05) among diets. Compared with the control, net PDV flux of glucose decreased (P < 0.001) when pigs were fed betaine, CLA, and betaine + CLA diets (37, 31, and 51%, respectively) and net PDV flux of NH3 decreased (P < 0.01) when pigs were fed betaine and betaine + CLA diets (29 and 40%, respectively). In conclusion, differences in net PDV flux of metabolites could explain metabolism divergences in pigs fed betaine or CLA diets.