Chemical and physiological behavior of feed carotenoids and their effects on pigmentation.

Feed carotenoids are not inert substances. In the metabolism of animals, they may undergo a large number of transformations. A number of these compounds have vitamin A activity. Those that have high vitamin A activity usually have fairly low pigmenting properties. Generally only monohydroxy- and monoketocarotenoids are converted into vitamin A. Generally plants synthesize optically active carotenoids. The laying hen is not able to transform all carotenoid configurations so that they can be used to increase egg pigmentation. Feed carotenoids occur in natural compounds in about 60 to 90% trans and 10 to 30% cis form. The trans form is a more effective pigment because of the redder hue and greater stability. Either the hen has the ability to convert some of the trans form into the cis form, or this transformation occurs in the egg yolk. The saponification process improves the digestibility of certain xanthophyll preparations. The efficiency of fat absorption in the hen also influences the deposition rate.