How do they get it?
A number of factorscontribute to the development of perineal hernias.  Genetic selection for low muscle mass in the rump area and male hormone influences are involved.
Environmental factors can play a role such as exercise and sudden impacting pressure to the abdomen.
Animals who have suffered trauma such that the intra-abdominal pressure suddenly rises can force abdominal contents through a body wall and into areas outside the abdomen.