The basic cause is thought to be excessive dietary energy intake. Hereditary tendencies vary among various strains of egg production stock, but heredity is not the entire cause for this malady. Laying hens housed in cages are most often affected since they are less able to get sufficient exercise and dispose of the extra dietary energy. Birds within a flock that are most often affected are the high producers. This indicates that physiological energy metabolism and production are closely associated with this condition.
Mortality varies considerably among flocks but can become excessive in some cases.
Death usually is caused by a fatal internal hemorrhage originating in a portion of the liver. This hemorrhage is often caused as the hen is straining to lay her egg and the enlarged, friable liver is more vulnerable to injury. When a large blood vessel ruptures, sufficient blood is lost to cause death of the hen. The primary treatment for this condition requires an alteration of the diet or amount of dietary energy consumed. Replacement of some of the corn in the diet with lower energy feedstuffs like wheat bran can provide a lower energy diet.