Mastitis is inflammation of the mammary gland (breast) and is almost always due to a bacterial infection. It occurs occasionally in mares nursing foals, most commonly in the drying-off period (the end of milk production, when the glands are reducing and stopping the production of milk). Mastitis can occur in one or both mammary glands in the udder. Milk from inflamed mammary glands may appear normal or may be abnormal in color or consistency. In the early stage of mastitis, the affected glands are hot and painful. Other signs of illness such as fever and depression may occur. The mare may walk stiffly or stand with hindlegs apart due to the discomfort. The disease is diagnosed by physical examination and blood tests. Mastitis is treated by the administration of appropriate antibiotics.