Mastitis is defined as inflammation of the mammary gland, usually due to microbial infection. Many organisms have been known to cause mastitis including bacteria, fungi, and yeast. Mastitis is the most economically important disease of the dairy industry, the condition has been estimated to cause as much as two billion dollars in lost income for United States dairy producers at a cost of $181 per cow per year. The biggest losses are due to lowered production, but discarded milk, drugs, veterinary costs, and premature culling also contribute to the losses. More than 130 different microorganisms have been isolated from the mammary gland of the bovine with the majority of infections due to staphylococci, streptococci, and coliforms. However, mycoplasmas have begun to cause significant problems in some dairies. The first reported cases of mycoplasma mastitis were in Europe in 1960. Since that time it has been found all around the world, including the United States. Traditionally, California was most affected, but the disease has now become a problem across the entire country.