A subject that frequently comes up in our daily lives as veterinarians is deworming. What should I deworm my horse with at this time of year? How often should I deworm my horses? Should I use the same dewormer all the time, or should I alternate? These are sometimes difficult questions to answer – but talking to your veterinarian before choosing a dewormer off the shelf may be the best way to protect your horse against parasite infestation in the future.

In the past, there have been many different theories about the best way to control parasite populations in horses. Historically, deworming products (anthelmintics) have been available for over-the-counter purchase at tack and feed stores – leaving horse owners to decide which dewormers to use, and how often to use them. Over the past 20-30 years, this means deworming has happened in a bit of a disorganized fashion – and unfortunately for us and our equine companions, has led to the development of resistance in our parasite populations to many different dewormers.

Parasitologists will point out that the main issue with parasite resistance is that there are NO NEW DEWORMING PRODUCTS currently in development. This means that what we have available on the market today is likely all we are going to have for the next 5-10 years – and we need to use these products wisely to ensure they keep working for us. The introduction of fecal sampling and improved environmental management will become important tools to fighting this war on parasites.

As veterinarians, we see the detrimental effects that a heavy parasite load can have on our patients – and a good deworming plan should play a role in the overall herd health at your farm. Even though you are free to pick up deworming products at the tack store, we are keen to help you design a deworming plan for your individual farm. This will include important things, such as when to deworm vs fecal sampling, which dewormers to use – and it may also include some easy-to-implement changes to your manure management system.

As a group at the KVC, we have been making a conscientious effort to incorporate fecal sampling (specifically fecal egg counts) into our deworming plans. This isn’t always the easiest thing to “sell” people on, as it means paying a fee for manure testing, sometimes in addition to the cost of a dewormer. On farms where deworming programs have been in place for a long time, and stocking densities are not high – fecal egg counts are often low, which means that for a certain time period the horse(s) will not need to be dewormed. However, in situations where the parasite burden is high – fecal egg counts allow us to target certain horses and certain parasites to quickly solve the problem. Our hope is that over time, this will save you money (or at least not cost you anything extra!) and lead to an improvement in health and performance of your horse(s)!

Please call us if you are interested in working on the parasite situation at your farm; however these are some basic guidelines to follow if you get stuck:

· In Ontario, we try to deworm or check a fecal sample 3-4 times per year (consider April/May, August/September and December/January)

· If a fecal egg count is done at the first two checkpoints, horses will only be dewormed if their results are greater than 200 eggs/gram of feces, and with a dewormer that targets the specific parasite. This is a more effective way of controlling the parasite population than randomly selecting a dewormer

· The “winter” deworming is often when we use a product that contains praziquantel (the names of the product usually have a “plus”, “max” or “gold” at the end of their names) – this will kill tapeworms, and also take care of any bots that may have been missed at other points in the year

· Young horses (less than 3 years of age) may need more frequent deworming/fecal sampling than adult horses as their susceptibility to parasites seems to be higher

· Picking manure out of your pastures can also minimize the spread of parasite eggs, and if done regularly becomes less of a chore

· “Dragging” or harrowing manure in the pasture is only advisable if the weather is dry, as parasite eggs are susceptible to drying out in the sun and will die. If the pasture is wet, the conditions are ideal for the parasite eggs to thrive – and the harrowing will simply spread them out across your pasture