Burmese Cat

　　Cats (and dogs) easily develop pyometra because their cycles are different from humans.

　　Humans menstruate regularly to expel the congested lining of the uterus prepared for pregnancy.

　　Cats, however, start bleeding on the first day of their cycle. Ovulation occurs later in the cycle, and regardless of pregnancy, the bleeding stops at the end of the cycle. The cervix closes tightly, the mucous membrane inside thickens and becomes congested, and is slowly absorbed on its own. Repeated heat cycles cause too much to accumulate, leading to pus formation that cannot be expelled, resulting in pyometra.