Oestrus control and the incidence of mammary nodules in bitches, a clinical study with two progestogens

The incidence, size and location of mammary nodules were established in 10 practices in The Netherlands by the clinical examination of bitches in which oestrus was controlled with proligestone (P), 331 animals, or medroxyprogesterone acetate (MAP), 341 animals and in 339 animals never medicated with such compounds. In comparison with the unmedicated control and the P-medicated animals of comparable age the incidence of mammary nodules of all sizes was significantly increased in the MAP-medicated animals. There was no significant difference in nodule incidence between the P-medicated animals and the control animals. Based on the assumption that nodules above a certain size are most likely tumours, these results indicate that oestrus control with MAP stimulates tumour development even in animals medicated for less than four years. The practical value of the reported differences, especially in relation to the subsequent requirement for surgical removal of tumours in bitches, medicated for oestrus control, is discussed.