Due to the fact that most Horses in Alaska are penned in a small area, parasite infestations are quite common.  In short, the pen becomes contaminated with parasite eggs and larvae - the horse will eventually nibble a tidbit that is contaminated.  The following is my recommendation as a deworming schedule.

A periodic Fecal Analysis for Parasite Eggs should be completed.  The American Association of Equine Practitioners (AAEP) outlines a strategic deworming protocol in the following link - Strategic Deworming

The following online services provide equine fecal testing for parasites:

Horseman's Lavoratory

Parascreen

SmartPak


Deworm as directed using an oral equine paste.  Rotate the type of deworming drug.  The following is a list of deworming drugs followed by  trade names:
                Ivermectin - numerous  trade names such as: Ivercide, Ivermax, Equimax
                Pyrantel Pamoate -  Strongid Paste (Pfizer Animal Health)
                Fenbendazole - Panacur Paste (Intervet/Schering-Plough Animal Health)

Always follow label direction for the dewormer

 Once a year use a combination product for tapeworms - drug name for tapeworms is Praziquantel

For additional information follow this link to:  Internal Parasites: Strategies for Effective Parasite Control, AAEP Information Article