What are the common symptoms of selenium deficiency in laying hens?

In selenium deficiency: exudative diathesis in young chicks and myopathy of the gizzard and heart muscle in young turkeys; in ducklings, selenium deficiency lowers plasma glutathione peroxidase and body weight gain, and increases mortality. Ducklings that die from selenium deficiency show necrosis of tissues such as the gizzard, small intestine smooth muscle, cardiac muscle and skeletal muscle, as well as symptoms such as hydropericardium and ascites. Vitamin E and selenium have a mutually coordinated role in the prevention of these diseases. Chicks with severe selenium deficiency show poor growth and poor feather development, fat indigestion, pancreatic atrophy and fibrosis, and reduced activity of the selenium-dependent glutathione peroxidase in the pancreas. According to relevant reports: continuous sampling studies were carried out on pancreatic lesions; the lesions began at 6 weeks of age, showing vacuole and hyaline body formation in the exocrine pancreas. As the deficiency develops, the cytoplasm degenerates until the acini are replaced by a ring of cells with fibrous tissue embedded in the center of the lumen, and the gland degenerates. Feeding 100 IU/kg of vitamin E and promoting its absorption with bile salts can maintain a high level of plasma tocopherol, which can greatly reduce the incidence of exudative diathesis. The pancreas of chicks does not show exudative diathesis before severe degeneration.