The Main Diseases That Affect the Mammary Gland Directly Are Mastitis (Prevalent in Dairy Cattle and Dogs) and Neoplasia (Prevalent in Intact Dogs and Cats)

The most important problems involved in the production of milk are those caused by inflammation of the gland (mastitis). One fundamental cause of mastitis is injury to the teat canal from the repeated stretching that occurs with the milking process.

One of the adverse consequences of mastitis is the formation of connective tissue within the udder as a result of the attempt of the gland to wall off the infection. The presence of connective tissue limits the area into which ducts and alveoli can proliferate, thus reducing the milk-producing potential of the gland. The mammary gland is an example of an organ (the eye is another example) where the elicitation of an inflam­matory response is often detrimental to the function of the organ. Thus, therapies directed toward the treatment of mastitis often combine antiinflammatory and antibacterial agents.

Another process that disturbs the structure of the mammary gland is neoplasia. In domestic animals, the dog is most susceptible to the occurrence of mammary tumors. 'Γhe exposure of the mammae to the ovarian hormones estrogen and progesterone greatly increases the chance of neoplasia. The incidence of mammary tumors is relatively low if the dog is Ovariectomized before the first estrous cycle, but it increases progressively through exposure to two ovarian cycles; ovariectomy has little effect on neoplasia if done after the third or fourth cycle. Some owners want their dogs to have one or two cycles before they are Ovariectomized. It is important for veterinarians to point out the beneficial aspects of ovariectomy before the onset of puberty because of the incidence of mammary neoplasia, as well as the usual benefits of fertility and behavioral control.