Determining if your horse has worms is an easy and important step to maintaining their overall health.
Parasites and horses--a relationship that goes all the way back to the dawn of time. The fact is, you can never kill all the parasites in your horse. And really, you shouldn't. Killing them all is like going around with a can of disinfectant spraying every conceivable surface for contaminants. But yes, you must keep the parasite population down if you want your horse to be healthy. Verifying your horse has worms is easy enough; destroying them can be trickier. First, look at your horse's faeces. This is often the easiest way. If you see anything that even remotely resembles a worm, no matter how small it is (and no, I am not talking about bits of hay--you can TELL if it is a worm), your horse is a nice reproduction factory for ascarids and strongyles.
Another easy way to tell if a horse has worms is to look at its overall condition. Does its tummy appear bloated, yet there are ribs visible? Does it have a dull hair coat, sometimes with long hairs mixed in with the short--even though it's mid summer? These are prime examples of what a horse looks like with a heavy worm-load. The worms are getting all the horse's nutrition. The horse might be eating all the time, but half, if not more, of what it eats is feeding the worms.
A guaranteed way to check on the worms in your horse is taking a fecal sample to the vet and asking them to do a fecal egg count. This will tell you how heavy a load of parasites your horse is carrying. Don't worry too much if your horse has some worms--that is normal--but too many is bad news.
Where there is horse faeces, there are worms. The faeces carries the eggs, which hatch and then the larvae climb to the top of the grass stems and wait to be ingested--then the process begins all over again. Clean up your horses faeces and compost it. The heat will kill the larvae. Some larvae can burrow into your horse's tissues and lie dormant for years; escaping your deworming program. It is important to kill these by using special de-wormers that you can buy from your vet and off the market--just be very careful to follow label instructions.
Worms are serious business, especially for young, old or sick horses. In the old days, when horses ranged all over for their food, they did not face such a health issue with worms, as the worm load was spread far and wide in the horse's manure, and a great many of the parasites died before being ingested on the grass by the horses. Now, we keep our animals penned up, and the worms get to reproduce like mad. In order to stay ahead of the game, it is important to keep your horses on a rotating deworming schedule. Check with your local vet on the best program for your area.
Be sure and contact your vet before you begin a deworming program on a new horse. You will want to establish how much of a worm load it is carrying before you kill them off. Too many worms dying at the same time can cause a horse to colic.