Ditto what everyone else has said. I had a map, have to see if I can find it and it shows all the states and when it's recomended to start and stop Heartguard treatments. Here in Bama, stop in Dec & start again in May, but I usually start in April...If your vet gave you samples, he should have suggested when you should start using it. Not sure where you are in KY & what the temps are like, so you may want to ask your vet about that...If I remember correctly, for mosquitos to breed, they must have continous weather over 65 degrees for a couple weeks, but don't quote me on that one. Age wise, you can start using the heartguard now, but if your temps are already dropping, it may not be necessary...