Written by: Dr. Jacquie Jacob, University of Kentucky
Gossypol is a toxic compound found in the cotton plant. Although it can exist throughout the plant (in the hulls, leaves, and stems), it is concentrated in the cottonseed. Two forms of gossypol exist: free and bound. The free form is the toxic form. Bound gossypol binds to proteins, making it nontoxic.
When cottonseed oil is extracted from whole seeds, cottonseed meal is the by-product. The cottonseed meal can contain higher levels of the bound form or the free form of gossypol, depending on which extraction method is used. When the older screen-press method is used, heat generated during the process increases protein binding and results in a higher level of the bound form of gossypol. However, the more common method is solvent extraction, which is a more efficient technique for removing the oil. Because no heat is generated during solvent extraction, it has a significantly higher level of free gossypol.
Cottonseed meal should not be fed to laying hens. Gossypol can cause extensive egg yolk discoloration and yolk mottling. Mottling refers to pale spots or blotches on the surface of the yolk. The spots can be transparent or brownish orange to almost black. A high incidence of yolk mottling does not affect the nutritional value or flavor of the egg but does decrease consumer acceptance.
The gossypol in cottonseeds is located in glands. New varieties of cotton have seeds with no glands. When cottonseed oil is extracted from these varieties, the level of gossypol in the cottonseed meal is reduced. However, even when these new varieties of cotton are used, the resulting cottonseed meal contains cyclopropenoid fatty acids, which can cause a pink discoloration in stored eggs.