White-tailed deer have two different coats of hair during the year. The gray winter coat is comprised of longer guard hairs and a soft wooly underfur that provide insulation from the cold. This thicker winter coat is shed prior to the hot summer months. This shorter summer coat is reddish-brown and lacks the thick insulating underfur. The summer coat hairs are short and wiry. A genetic defect produces a few white-tailed deer that are brown and white spotted, similar to a pinto horse. These white-tailed deer are called piebald. In addition to the coloration deficiency, many piebald deer have skeletal deformities such as short legs, bowing of the nasal bone, arching of the back bone and heart defects. Piebald deer make up less than one percent of white-tailed deer herds.