Quite honestly, ALL of the above information is outdate, archaic, and/or ineffective. The newest recommendations, put forth by the American Association of Equine Practitioners, call for an individually tailored deworming program for each horse, as not all will shed or carry parasites in the same manner. To ensure an effective regimine, and to prevent dewormer resistance, you are not supposed to medicate until first doing a fecal egg count. Then, the vet will determine exactly what is residing in your horse's gut, and prescribe the appropriate chemical. Depending on your horse, yes, it is very likely that, using this protocol, you will only be deworming 2-3 times per year, and not necessarily on a rotation.