Dr. David Laird of Texas is nationally recognized for his expertise on internal parasite control and most recently for his work on encysted larvicidal treatments for cyathostomiasis, a condition that leads to poor performance and colic in horses:

According to Dr. Laird, Quest (moxidectin) in reality will only kill about 15% of the encysted strongyles, whereas Panacur (fenbendazole) will kill a much higher amount than that and is also a lot safer then Quest/moxidectin (note: Panacur and Safeguard are identical products with different trade names the chemical name for both Panacur and Safeguard is "fenbendazole").

Dr. Laird devoted most of his discussion to the life cycle of the small strongyle worm. When your horse goes out to graze in the pasture or picks around in his stall or paddock, he is ingesting thousands and thousands of larvae that can stay alive on the ground for up to a year.

The little larvae move along your horses digestive tract until it comes to his cecum and colon. Then it penetrates the fenbendazole 222 mg of the cecum or colon and stays there for a minimum of 45-60 days and as long as 2 to 3 years. Impossible, you think. You worm religiously every 8 weeks, right? There is no way those larvae can live in there if you worm every 8 weeks. Besides, there are plenty of wormers that kill small strongyles. Heck, they ALL kill small strongyles. Right?

Right... however, they only kill the ADULT worms, or larvae that have not yet burrowed into the lining of the cecum and colon of your horse.

These larvae are known as encysted larvae, and Dr. Laird likened them to a hibernating bear. He explained that they have a very, very slow metabolism. When you worm your horse, that wormer is in your horse's gut for about 18 hours. Because the encysted larvae have a very slow metabolism, the wormer simply doesn't do the job over an 18 hour period. It doesn't effect the little guys. So, the encysted larvae sit there making waste in the lining of your horse's gut, and when they finally decide to emerge into your horses stomach, they leave behind all this cellular debris, and this is whenyour horse can get sick. This condition is known as Cyathostomiasis (small stronyle infection).