I'm not trying to slam the people that deworm every month....just giving my and my vet's opinion on the subject but....its amazing now a days how many people still deworm their horses monthly or every other month. I am for one, against deworming on a monthly or every other month basis. It is sooooo unhealthy for horses to be dewormed every month!!!!! Exspeccially when most of the time the horse does not even need to be dewormed. People are shoving poisen and chemicals down their horse's throat on a monthly basis that the horse typically does not even need. People don't know for sure if the horse has the type of worm that they are deworming for. So if that type of worm is not even in the horse's body, the dewormer that you are giving them is doing no good. I might not be a professional...or a vet, but to me, giving horse's a poisenous substance when it might not be nessacary....has to be unhealthy. My vet agrees.
So...what is a healthy way to deworm horses? Fecal exams. Most vets recommend doing a fecal exam twice a year....once in the spring and once in the fall. They are $20 around here. Basically the vet looks at the fecal sample and determines which worms the horse has. Then you worm accordingly. This way you know exactly what to deworm for...and your giving your horse the correct dewormer. No guessing....no unneeded chemicals, poisens or dewormers....and it can cut down on costs. You will also be surprised occasionally when getting fecal exam results back. Most of the time(at least for me) my horse's fecal exams will come back with no high levels of worms that I would need to deworm for. So they might not even need to be dewormed!
But again, every owner has their own opinions on this subject. And every owner should make there own decisions on what works for them and their horses...and what they believe is right or wrong. In my opinion, I believe that doing fecal exams and then deworming accordingly is the healthiest way to deworm my horses.