To effectively de-worm a horse you need to know the weight of the horse. Many problems can arise due to de-worming with an inappropriate dose. Use a weight tape, available through many feed companies, to determine the correct weight of your horse. Most weight tapes can be off by as much as 10% so it is a good practice to add 200 lbs to the tape weight for an adult horse and de-worm your horse for that amount. The present de-wormers have a very large safety margin so giving your horse more than it needs is typically not an issue. De-wormers with Moxidectin have a lower safety margin so de-worming small horses and ponies requires a more accurate dosing. Make sure that the horse's mouth is free of grain or hay through rinsing or making sure it has not just eaten. Dial the syringe to the appropriate weight, from the weight tape + 200 lbs. Standing off to the side of the horse's neck, stick your thumb in the horse's lips towards the back of the mouth. Push the de-wormer syringe past the thumb into the horse's mouth and deposit the substance. If the horse should spit the substance or part of the substance out, make sure to deposit more paste in the mouth to cover what was lost. Record weight, substance, and date in the horse's records. Additional information is available at the links listed below.
There is extensive information on this topic on the eXtension (pronounced e-extension) web site. The specific pages are:
Management and control of internal parasites in horses
How to administer deworming medicine in horses
Once you have read that information it is always a good idea to consult your local veterinarian because they are the experts on equine internal parasites in the environment in which you live. As animal health experts, they can design an effective parasite control that fits in a total preventive health plan to maximize horse’s health.
