Mastitis is an infection of the mammary glands. It is particularly common in nursing and milking cows. When a cow develops mastitis, her teat and udder often become red, inflamed, and painful. She may not allow you to milk her, and she may not allow a calf to nurse. There is an antibiotic medication called quartermaster that can be delivered straight into the udder, through the teat. This medication can be quite effective at alleviating mastitis and its symptoms.