Aortic atherosclerosis in nonlaying hens with fatty liver syndrome

Ten laying hens with low plasma cholesterol levels and no signs of fatty liver syndrome were examined at necropsy. Liver coloration and deposition of body fat were not abnormal in such hens. Eleven nonlaying hens had signs of fatty liver syndrome. They were out of production for 1 to 3 months and had elevate plasma cholesterol levels. At necropsy, such hens had yellow livers, heavy deposits of body fat, and several involuted egg yolks, which were dark yellow. Intimal plaques were observed by light microscopy in the abdominal aortas of hens with low plasma cholesterol levels; the plaques contained little or no lipid and were composed of three or four rows of modified smooth-muscle cells. Aortic intimal plaques of hens with high plasma cholesterol levels were composed of 16 to 18 rows of modified smooth-muscle cells when examined by light microscopy. The plaques contained intracellular and extracellular lipid, indicating aortic atherosclerosis. Electron-microscopic observations of the abdominal aortas of both groups of hens were similar to light-microscopic observations, except that lipid, including cholesterol clefts, was seen both intracellularly and extracellularly in the thickened tunica intima of hens with high plasma cholesterol values. Thus, the presence of aortic atherosclerosis was confirmed by electron microscopy. It is suggested that the endogenous hypercholesterolemia and cessation of egg production, characteristic of severe fatty liver syndrome, originated from the reabsorption of involuted egg yolks and that such reabsorption caused the development of aortic atherosclerosis and deposition of excess body fat.