My PERSONAL opinion is that we *may* be 'overdoing the deworming in SOME circumstances, and that perhaps it may not be necessary to deworm every 6-8 weeks, as is the common recommendation. Now, I am talking about otherwise apparently healthy adult equines. I am a STRONG believer that good husbandry plays a BIG part in keeping the exposure to reinfestation down, and I work VERY hard at that, cleaning up twice daily EVERY day.
I know it may be much harder for those who pasture their horses; I almost never do, as I live in drought-stricken central NM, and although I have 10 acres, about 8 of which 'can be' available to graze when Mother Nature has cooperated by sending rain for the native grasses. Where there is plenty of rain, and grass nearly or always grows, sometime lushly, there is a MUCH higher exposure to worm eggs-I understand that! But, I also know that there is LOTS of advice 'out there' about managing pasture to minimize exposure to worm eggs--such as proper rotation, and dragging of the pastures to break up manure--and believe that doing ALL of those things can be one of the biggest aids in keeping worm numbers lower in your horses.
All of my horses are in dry lot-and I do mean DRY! I clean up before the manure gets 'broken up' and reduced to 'powder', which can later be ingested as they 'piece around' on the dirt. I ALWAYS feed in feeders, and most places, have also put down mats where they eat(which I sweep daily, also--don't need colics from 'sand'/dirt accumulation--I do use psyllium monthly for a week, even so--some horses are notorious for 'vaccumning' the ground!).Though I have in past used a manure speader and spread the manure both in my arena, and on my 'other' 5 acres(which I seldom graze; see above!), now that I only have minis, I am able to have all of the manure hauled off by my trash service every week(costs extra, but still, worth it!)--so no more manure is 'accumulating' here. Other benefits include a VERY low fly population, in spite of the fact that my neighbor piles his manure in a bin for a year or more at a time, which the breeding flies just LOVE...(GRRRR!)
Honestly, I am just as glad I live in a summer/hot, winter/COLD, and dry, climate, for it is more difficult for parasites of many types to 'prosper' and reproduce in such a climate!
I deworm only about three/four times yearly, depending on how much moisture and/or heat we've had. I have been told more than once by various vets that fecal egg counts may not be of all that much help. The intensive husbandry just takes MY time and effort, which I have and am willing to utilize; I do NOT have much money, especially as everything is skyrocketing in cost, including vet charges---so it is really my only choice to utilize that time and effort of my own.
Just my opinion and experience....I should add that I'd urge EVERYONE with horses to consider their OWN 'unique' situation---heat/cold, humidity, annual moisture received from all sources, how you 'keep' your horses, and all the many possible variables, and set up an overall 'horse husbandry' program based on that!
Margo