If the hormones aren't present the chances of pyometra are very rare.
Here is a quote>"Pyometra. Meaning "pus in the uterus," pyometra is a common disease of intact bitches, usually affecting individuals over six years of age. This condition develops as a result of the influence of progesterone on the uterus during diestrus. Progesterone promotes growth of the endometrium (the lining of the uterus), and secretion of uterine glands. These secretions provide a me-dium for bacterial growth. In addition, progesterone inhibits the infection-fighting activities of uterine white blood cells. |