COOPERATIVE EXTENSION SERVICE . DEPARTMENT OF ANIMAL SCIENCES . PURDUE UNIVERSITY
poultry for profit
P-94
January, 1971
Egg yolk mottling
By Joe Berry Extension Poultryman
"Mottled yolks", that is, egg yolks which exhibit abnormal coloration, are often objectionable to the consumer and prove a loss to the producer. Even though mottling damages only the esthetic value and not the nutritional value, there is a real need to prevent this source of loss to producers.
There is no clear-cut answer for the problem of yolk mottling. Several factors are known causatives. Among the worst are:
(1)	Cottonseed meal (containing the pigment gossypol)
(2)	Nicarbazin (a drug used to control coccidiosis)
(3)	Dibutyltin Dilaurate (a worming compound).
Probably the most severe mottling results from the inclusion of cottonseed meal in the layer ration. The pigment, gossypol, contained in the cottonseed, is the causative agent. Meal from glandless cottonseed, which contains no gossypol, has been successfully included in the layer ration with no mottling.
It has also been reported that certain iron-containing compounds tie up the gossypol and prevent mottled yolks.1 The
mottled yolks caused by gossypol often have dark green areas, and in some extreme cases are almost completely black.
Research has shown that there are large differences between hens which produce eggs with mottled yolks when cottonseed meal is fed in the layer ration. One report indicates that more than 88 per cent of the eggs from one hen showed severe mottling, while less than 2 per cent of the eggs from another hen on the same ration exhibited similar discolorations.
Eggs suspected of coming from hens being fed cottonseed meal can be checked by placing them in an ammonia atmosphere. The yolks will turn dark rapidly if the eggs have come from the hens on a ration containing cottonseed meal.
Nicarbazin, a coccidiostat, is also known to produce mottling. The recommended level of .0125 per cent has been reported to have produced mottled yolks. It has also been reported that the temperature of storage will greatly influence the incidence of mottled yolks from hens being fed Nicarbazin. Those eggs held at 50°F have been found to contain less mottled yolks than those held at room temperature.
Length of storage has also been shown to influence the incidence of mottling.
Cooperative Extension Work in Agriculture and Home Economics, State of Indiana, Purdue University and U. S. Department of Agriculture Cooperating. H. G. Diesslin, Director, Lafayette, Ind. Issued in furtherance of the Acts of May 8 and June 30, 1914.