The chance of your dog developing mammary cancer if you get her spayed before her first heat is 0.05%. This is a very low number. If you wait till after her first heat this number jumps to 8%. If you wait till her second heat it jumps to 26%. This is very significant. Unless you are planning on having a litter then my strong suggestion is to get your female dog spayed at 4-6 months. Hopefully you find this information helpful.