PetTrust or TriHeart Plus (generic analogs for Heartgard) costs $30 for 6 months at WalMart pharmacy with a vet's RX -- literally $5 a month. If you get the RX with one refill, they'll dispense two boxes -- a year's worth -- for $60.
I'm the one who posted about lifecycles. Your last pill in Oct. may not kill 100% of the HW babies from Sept. mosquitoes that bit the dog--resistance is growing, and even in non-resistant areas, a tiny percentage can slip through. That's okay, though, as they are designed to mop up any that slip through the next month. Year round prevention guarantees none slip through long enough to grow too big to kill with prevention.
However, if you stop in Nov. after your last dose in Oct., any that were deposited in Sept., but not fully killed off with your last dose, will grow all winter long and be too big to kill with preventative in March. You won't know your dog is positive yet though -- it might not throw a positive test until May (as worms have to be 7 months old to throw enough antigen to turn the test positive -- but even 3-4 month old worms are too big to kill with prevention). If you do your annual test every March, you won't know until March the following year, even though the dog has been positive all along. By then, you've got big, adult worms, possibly clogging up pulmonary arteries. You will spend around $1,000 to get rid of them.
If you want to stop at some point, I think it would be more conservative to keep giving it at least a couple of months beyond the point of hard freezes and bug die-off. Be sure you've mopped up all those autumn larvae and no stragglers survive the winter inside your dog.
Stopping in early Fall, you are rolling the dice and may get lucky...esp. if you have very low natural HW reservoirs in your population, and no one is transporting dogs up from the South into your communities. For $5 a month, though, it's such an easy chance to avoid taking. The dose of those generic ivermectin products is incredibly low (that's why some HWs slip through -- the ultra low dose that's even safe enough for MDR1 dogs).
I'm all for finding a vet you like and trust (and I wouldn't use VCA either, given their business model). Vets aren't wrong to take HW seriously though. I deal with treating way too much of it in rescue, and it's a mess.
Last edited by Magwart; 03-02-2018 at 07:42 PM.