Parasite infection on free-range and floor-reared chickens showing discoloration of egg yolk

A significant discoloration of egg yolk was found in a group of free range or floor-reared chickens. There was no egg yolk discoloration in conventional caged chickens in the same farm. The deficiency of some pigments in the ingredients of diet may not be the cause of this problem, because the same diet was fed to both free-range and caged chickens. Malabosorption caused by reovirus was suspected, and ELISA test was performed, but the result was negative. Although coccidial infection was found in some cases, the group without the evidence of coccidiosis also had discolored egg yolk. The parasitism of Raillietina tetoragona, Ascaridia galli, Capillaria obsignata, and Postharmostomum gallinum was detected in layer flocks showing discolored egg yolk. Parasitism was detected in most of layers showing egg yolk discoloration.