There is this book its called "Horses a guide to selection, care and enjoyment" by J. Warren Evens. Its a VERY comprehensive book and I reference it for everything. It has feed requirement charts and the nutritional composition for pretty much everything we feed to our horses. It also has a detailed description of how to do your own fecal floats.. It seems fairly simple and would do it if I still had my microscope. Basically its taking a ball of poop soaking in a certain amount of water and then counting a number of worms you see on a slide and if you get a certain amount over #### you need to worm your horse.
Sorry for the nondescript but I"m too lazy to go grab my book, search for the info and jot it down. The book is wonderful though... it was a college text book for my stable management class.