mammary cancer as after 2 or more heats the chances remain 1 in 4 or 25% as compared to a spayed female that never had a heat cycle. But Pit Chick just gave 3 other good reasons for spaying.

The healing might taken closer to 2 weeks instead of 1 week in a dog that age. The good news is that an older dog won't be bouncing off the walls with energy like a puppy. So you won't have to worry about over exertion during recovery.