Male domestic cats

Question
I have two male tabby cats aged 4 and 1. We have had the 4 year old for 3 years and the 1 year old for just 4 months. Why does the 1 year old constantly smell the butt of the 4 year old? They seem to like each other since they play together most of the day and they also choose to sleep close to each other as well, as if to stay warm. Could this butt smelling be associated with acts of dominance? Thanks Rose

Answer
Hi Rose.  This isn't a dominance behavior but is a nonconfrontational method of collecting information.  Cats become familiar with each other through sniffing one another's anuses to pick up each other's scents.  But they can gather information even beyond this.  They learn where the cat has been, as scents are picked up from wherever the cat sits, and especially in the case of outdoor cats, wherever the cat rubs up against or sprays.  Cats could also get an idea as to the health of other cats by butt sniffing, as diarrhea or foul-smelling or dilute urine can indicate illness.  Some people even believe that cats can detect richer food sources with this behavior.

It's possible that your 4-year-old is leaking some anal fluid, a liquid produced by anal glands and stored in sacs just inside the anus.  Anal fluid is normally expressed from these sacs during regular bowel movements.  But some cats produce too much fluid, or their stool is too soft to empty the sacs regularly, and the fluid leaks out throughout the day.  Although it smells horrible, any type of discharge like this is attractive to other curious cats.  If you notice any kind of strong odor coming from your 4-year-old's back end, you may want to have him checked out by a vet.  Anal sacs can be manually expressed by the vet.