This is just so funny. I started the same sort of thread today, because I'm thinking the same way. I did call a vet and they are researching if lyme and heartworm are both controlled by heartguard, they suspect it is, but who knows anymore. The reason its year round basically boils down to making up for the owner not giving it the right way. If there are no mosquitos, how necessary is it, I want to know this too. The vet I spoke to said they look for 2 weeks of 60 plus degree days to start medication and they do every 45 days instead of every 30 days. Another article said they based it on 64 degree plus night time temperatures.
Thoughts on Heartworm Doses? MOVED FROM GEN INFO