Variations in the Composition of Egg-yolk Pigment

Gillam & Heilbron (1935) in a study of the effects of feeding maize and grass on the composition of yolk pigment have shown that xanthophyll is the principal pigment of egg yolk, although cryptoxanthin and B-carotene are also present, the former sometimes in amounts that contribute appreciably to the total vitamin A activity of the yolk.In view of this, the extent of the variations in the cryptoxanthin and B-carotene of the yolk is of considerable importance, particularly the variations that may be experienced under the conditions normally adopted for poultry breeding.In the management of breeding stock the hens are almost invariably allowed free range over good pasture, the grass supplying a considerable, and often the greater, part of the hens' requirements for vitamin A.In a previous paper (Grimbleby & Black, 1950) an experiment was described in which the variation in pigment and vitamin A contents of individual eggs was examined, the eggs being obtained from four birds taken from a breeding flock of Rhode Island Red hens fed on a pigment-free diet but allowed free range over good pasture.No vitamin A supplement was given.The yolk pigments from individual eggs were fractionated, xanthophyll, cryptoxanthin and 8-carotene being separately determined.According to Kuhn, Winterstein & Lederer (1931) the so-called yolk 'xanthophyll' is a mixture of lutein and zeaxanthin, but the separation of the xanthophyll fraction into these components was not attempted.The vitamin A content of the yolk was also determined and the significance of the variations in total pigment and vitamin A contents of egg yolk was discussed.The present paper deals with the variations in composition of the yolk pigment found in the same experiment.