cats and catheters

Question
why do vets put a cath in the cats rectum

Answer
To be completely honest, I haven't the slightest idea why a vet would put a catheter in a cat's rectum.  Are you sure they weren't administering an enema?

They may catheterize the urethra in order to obtain urine samples or drain the bladder when there has been a blockage.  But I'm not sure what good a catheter would do in the rectum.