Ok now there seem to be a couple different schools of thought here, so I thought I would get some opinions.
School#1 (old school): Deworm about every 2 months (6-8 weeks), rotate through the different types
School#2 (new school): Deworm only about 2-3 times per year, no dewormer needed from Oct-Feb (in the northern states anyway where we get the deep freezes)
The thought behind this new school of thought is that worms are becoming VERY resistant to what we currnently have and deworming as often as we are doing is making it worse.
How often do YOU deworm your horse?