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Ceres
Birds produce a white powder, which covers the eye and nose ceres. They fail to produce this when sick and so the ceres become dull. In addition, with respiratory infection, they become stained with discharge. Inflammatory material that forms in the sinuses drains underneath the nose cere and then through the slot in the roof of the mouth into the back of the throat. As this material flows under the nose cere, the cere acts like a sponge, absorbing this material, which stains it various shades of brown depending on the volume of material present. Not all ‘less than white’ ceres, however, indicate a problem. Rain can wash off the white powder covering the cere, exposing the red blood below to give the cere a pink hue. Also, young hens can lose this white powder through excessive billing."
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