When we get a new horse into the farm the first thing we do is worm him and get his teeth looked at by the dentist. We always assume the horse has worms. Work with your vet to determine the best way to clean the worms out of your horse. Below is how we approach the problem of worms. We are not veterinarians and we are not offering medical advice. Contact your vet before trying this or if it the horse is not healthy which is often the case when a horse has been rescued.
Thoroughbreds that have not had the proper nutrition can have many problems that need to be addressed by your veterinarian. Trainers racing Thoroughbreds at the bottom tier tracks often do not have the money for extra supplements or quality feed. That is why we do not get our horses at these tracks.
We start the worming process with a pellet wormer such as Strongid C2X. Since pellet-based wormers are mixed with a horse's feed daily, the potency is far lower than actual pastes. This lower potency allows for a slower and healthier parasite kill and removal rate. I advise putting a parasite-infested horse on a pellet-based wormer for at least one week before advancing to the standard paste regimen. Strongid is a pyrantel tartrate based product.
You must be careful to apply the recommended dose of horse wormer with each session, because parasites possess the ability to build a resistance towards agents designed to kill them when the agents are not applied in doses strong enough to kill the parasites outright. This is why it is also important to rotate the various types of horse wormers – not only does it increase the spectrum of targeted parasites, it makes it difficult for parasites to build up any sort of resistance or immunity.
In about two weeks, give an ivermectin based product with praziquanel which is proven to have a wide margin of safety and is highly effective in controlling tapeworms in horses.
Finally, do a Panacur PowerPac which is Fenbendazole double the normal dose and given for five days in a row. (Safe-Guard is also Fendbendazole.) Use it for the control of large strongyles, encysted early third stage, late third stage and fourth stage cyathostome larvae, small strongyles, pinworms, ascarids and arteritis caused by 4th stage larvae of Strongylus vulgaris in horses. When the worms are encysted in the walls of the intestine it can interfer with the absorption of food.
DO NOT DO A PANACUR POWERPAC until you have cut the worm load down with two other classes of wormer. You can colic your horse and kill him if too many worms are killed off at once.
A high fat, high fiber diet will help to assure good weight gain after checking the teeth and doing the worming rotation. If the horse is still not doing well, contact your vet and get a blood test done to rule out any other illness or underlying problem.