Abnormal Yolk Color and Mottling Caused by Dietary Tannic Acid and “Tannins”

Abstract Field observation of hens’ eggs with olive green yolks produced by ingestion of Red Gum (Eucalyptus camaldulensis) sawdust litter is reported. Subsequent work on the effects of dietary tannic acid and “tannins” (total phenolic compounds) in Red Gum sawdust on yolk discoloration and mottling is reported also. A dietary level of 0.05% tannins from sawdust resulted in mottled yellow yolks while 0.5% tannins gave olive green yolks. The lowest level of tannic acid (1.5%) produced firstly mottled yolks then green yolks. Evidence that dietary tannic acid and tannins interfere with pigment metabolism is presented. Possibly this could lead to commercial problems when feedstuffs containing high levels of tannins are used in laying rations.