Exploring diet effects on the profile, excretion and enterohepatic circulation of bile acids in the chicken

Beyond their role in lipid digestion, the physiological function, distribution and composition of bile acids (BAs) in poultry remain insufficiently understood. We investigated bile acid metabolism in broiler chickens as well as laying hens in response to different diets. Two experiments were conducted: the first was a digestibility study of both genotypes fed either a highly digestible or challenge diet to assess the effect on fat digestibility and fecal bile acid excretion. In broilers, the highly digestible corn-soy diet improved fat digestibility and increased plasma triglycerides and non-esterified fatty acids (NEFA), whereas laying hens showed limited dietary effects. The bile acid excretion correlated only weakly with fat digestibility in both species. In the second experiment with broilers, BAs were measured in different matrices: gall bladder, intestinal content and mesenteric and peripheral blood pools. All pools were dominated by (tauro)chenodeoxycholic and taurocholic acid. Intestinal reabsorption of the conjugated BAs was far more efficient than the deconjugated BAs. Diet did not affect intestinal or circulating bile acid concentrations. Bile acid concentrations in peripheral circulation resembled the concentrations in mesenteric veins. In birds, fat digestion is less likely driven by the enterohepatic cycle. Instead, BAs appear to circulate more openly in peripheral circulation indicating that avian bile acid metabolism could be more complex than in mammals and cannot alone explain diet-induced differences in fat digestibility.