The uterus is generally filled with pus. Although the disease has been recognized for decades, the true pathogenesis has still not been completely understood. It is generally recognized that progesterone and estrogen and their receptors have a role in the development of pyometra; however, the infection is triggered by bacterial involvement. The cyclical hormonal influences of the female dog allow the uterus to go through changes that will be acceptable for fertilization of an embryo. The changes that the uterus undergoes are typical for each dog. If bacteria are introduced into the uterus at a certain time during the cycle, hormonal regulation of the uterus allows the infection to start and become fulminate.
NB: Ovariohysterectomy (spaying) surgery is the treatment of choice for these patients and can be life-saving. Surgery however, may not be desirable, e.g. in a valuable breeding bitch. There are other conventional options, and I have succesfully treated some pyometra patients strictly with homeopathy (and close monitoring).--Dr. Jeff