Signs of selenium deficiency may be non-specific and look like any other cause of general ill-thrift. Animals may show reduced wool and/or meat production, poor immunity (shown by increased levels of mastitis or faecal worm egg counts for example), reduced reproductive efficiency, weak or stillborn calves or retained foetal membranes in cattle.
One presentation of selenium deficiency which is strongly indicative of a deficiency is White Muscle Disease (WMD). WMD results in the destruction of normal skeletal and cardiac muscle. Animals can show muscle pain, lameness, reluctance to move, stiffness, proppy gait and even death especially if heart muscle is involved. On necropsy, the affected red muscle tissue appears pale and is sometimes described as like fish flesh in appearance.