The effects of a dietary antimicrobial on the biological half-life of chenodeoxycholic acid and plasma bile acid concentration patterns in the young pig.

Carbodox (CX), an antimicrobial agent, was fed at 0 or 58 ppm in a 19.5% crude protein corn-soybean metal diet to young pigs (12 to 15 kg). Radiolabeled chenodeoxycholic acid (CDC) was infused into the hepatic portal vein; after each of the subsequent six meals, blood samples were collected from the anterior vena cava (VC) and the hepatic portal (HP) veins. For the first 5 min after CDC infusion, the level of radioactivity in the CX pigs was significantly lower in the HP plasma and the slopes of the two curves of the plasma activity for the first hours were significantly different. The plasma bile acid concentrations (as measured by radioactivity) were significantly higher in the CX-treated animals following all meals. The biological half-life of CDC was 6.4 d in the controls and 5.7 d in the CX pigs. The increased rate of excretion was significant. These data indicate that bile acid metabolism in the young pig was significantly affected by feeding a subtherapeutic level of the antimicrobial CX.