The information I use came from an article I printed off in 2001, which cited several reliable and verifiable sources-including information from Hoechst(mfg. of fenbendazole), and an article by Karen Hayes, Idaho-based equine DVM,MS. I have never seen anything to contradict this information-and it was obviously written in and for the US/North America. It quite specifically calls for a 5 day DOUBLE dose, by weight, of fenbendazole, to achieve optimum kill-off of "encysted cyathostomes(small strongyle larvae)"...I have never read or seen anything that says that you will 'see' such larvae visible in the manure, though, even after 'kill-off'. Personally, I have not 'seen' ANY kind of parasite in any of my horses' manure for YEARS--but this doesn't mean they are always, or completely, parasite-free (though I can say, I have had NO bots here for a number of years now--how do I know? NEVER a bot fly, NEVER a bot egg on ANYBODY, for years! I am lucky to be in an area where only a couple of other horses are close by, and their owner has a good deworming program, as do I--so,VOILA! No bots, at least, not for now!) I believe that even a fecal is only a 'snapshot' of that particular 'batch' of manure, on that particular day, so is NOT absolute proof of the absence of worms -though it may 'prove' their PRESENCE! IMO, you really need to do all of the procedures to minimize infestation/re-infestation--such as: prompt manure removal and disposal from dry lots, proper manure spreading and pasture rotation/rest if you have pastures, not feeding off the ground, 'quarantine' of new stock and thorough deworming of such stock BEFORE they join the 'herd' in pasture or paddock--and so on---know your own circumstances, and tailor your deworming program accordingly.
The 5 day, double dose program of fenbendazole to 'get' encysted small strongyles, AND the two day, double dose program of pyrantel pamoate to 'get' tapeworms, are both recommended in the treatise I have, and are recommended for twice yearly. Because I live where it is very DRY, and gets both HOT in summer and COLD in winter, and I do ALL of the above, religiously, I do these particular programs only ONCE a year, because I feel that is sufficient for MY particular circumstances. If you live where it is more humid,have irrigated pasture, and/or it is temperate year-round, you might well need to do it twice a year. Most parasites LOVE moistness and warmth(not necessarily HEAT!), and temperate climates, but DON'T do nearly as well in very DRY climates or conditions, nor do they 'like' temp extremes of hot OR cold....though some eggs can persist for long periods of time, waiting for 'better' conditions. Against harmful parasites, it is a 'war', and we need to fight it vigilantly but with thoughtful care!
Margo
