Pyometra is an infection of the uterus in intact (un-spayed) female dogs and cats. This condition primarily affects middle aged to older female dogs and cats. Development of pyometra is hormone dependent and typically develops during the period of diestrus. Diestrus follows a heat cycle (estrus) and usually lasts for 60-90 days. During estrus, the cervix dilates in the female allowing for bacteria to ascend into the uterus. Read more about Pyometra