Unfortunately, there is no clear-cut answer to that question. Traditionally, it has been recommended that horses be dewormed every two months to control the wide range of internal parasites that can afflict horses. Recent discussions have led to another train of thought when deworming. As parasite resistance to dewormers builds up some horse owners now rely on fecal egg counts to determine when/what to deworm their horses with as opposed to the traditional two-month dewormer rotation. Whichever method you choose for keeping your horse parasite free, it is best to discuss it with your veterinarian first. Your vet will know what parasites are a problem in your specific area and help you determine which method is best for caring for your horse.
Traditional rotational deworming involves deworming your horse every two months. Rotational deworming attempts to control a broad spectrum of internal parasites that affect horses by rotating dewormers with different active ingredients that target specific parasites. Below is a chart that you can reference if you are following a traditional deworming schedule. However, keep in mind that this chart is for your reference only and it is recommended that you discuss your horse's deworming schedule with your vet before treating.
| Time of Year | Compound | Recommended Product |
| January/February | Pyrantel | Exodus, Quest Plus |
| March/April | Benzimidazole | Safe-Guard |
| May/June | Ivermectin | Agrimectin |
| July/August | Pyrantel | Exodus, Quest Plus |
| September/October | Benzimidazole | Safe-Guard |
| November/December | Ivermectin | Agrimectin |
The next method for deworming horses involves having a vet analyze your horse's fecal egg count. Having this done will help diagnose which parasites need to be treated as well as determine how effective your deworming program is. If you decide to control your horse's parasites by using the fecal count method then be sure to order the appropriate dewormer after consulting with your vet. Refer to the chart below to see which dewormers target which parasites to determine which dewormer will work best for your situation.
| Dewormer | Active Ingredient | Parasites Targeted |
| Agrimectin | Ivermectin | Large and small strongyles, Bots, Pinworms, Ascarids, Threadworms, Pinworms, Small bloodworms, Hairworms, Lungworms, Large-Mouth Stomach Worms. |
| Exodus | Pyrantel Pamoate | Large and small strongyles, Pinworms, Large roundworms |
| Quest Plus | Praziquantel/Moxidectin | Large and small strongyles, Encysted cyathostomes, Ascarids, Pinworms, Hairworms, Large mouth stomach worms, Stomach bots, Tapeworms |
| Safe-Guard | Fenbendazole | Large and small stongyles, Pinworms, Encysted Cyathostomes, Ascarids |
Having your horse on an appropriate deworming schedule will go a long way in keeping your horse happy and healthy. Keep in mind there are ways other than deworming to keep the parasites in check. Good pasture management will also help reduce larvae and eggs that can infect your horse. Rotate pastures that horses are turned out in if possible. Keep pastures mowed or harrowed. Remove droppings from the fields. All of these things will make pastures less "parasite friendly". Keeping stalls cleaned and enforcing an insecticide program (whether that be fly baits, traps, or spray) will also help reduce the parasite numbers around the barn. Above all, don't be afraid to consult with your vet with any questions you have about parasite control.
