Canthaxanthin as a model for the study of utilization of oxycarotenoids by chickens

A white corn-soy diet amended with varying levels (0, 5, 10, 20, 40, and 80 ppm) of canthaxanthin, a red diketocarotenoid available by chemical synthesis, and fed to young broiler chickens for 3 weeks has the attributes of a useful experimental model for the study of absorption, transport, and deposition of oxycarotenoids. On high pressure liquid chromatography of extracts of the diet and tissues of the birds, canthaxanthin predominated over the background level of nonspecific carotenoids. The concentrations of canthaxanthin found in the contents of the jejunum and large intestine and in the serum, liver, and toe web were directly proportional to the dietary concentration. Departure from such linear relationships would signal loci of action for factors affecting pigmentation. Analysis of toe webs, an integumentary depot site for carotenoids, revealed that the concentrations of canthaxanthin and two other compounds, one more polar and the other less polar than canthaxanthin, were proportional to the dietary concentration of canthaxanthin. Saponification converted the less polar compound to the more polar compound. The behavior of these compounds in response to dietary canthaxanthin, to chromatography, and to saponification can be explained by assuming that canthaxanthin, a diketocarotenoid, was partly reduced to a ketohydroxy carotenoid (hydroxyechinenone) whose hydroxyl group is acylated to form an ester. These products represent new metabolic reactions in poultry.