Dr. Tania Sundra

06 August 2019

11 Simple Rules for Deworming Your Horse

We understand that change can be hard, especially for horse owners. We are used to following management practices that have been done for generations. However, there has been a paradigm shift when it comes to deworming and if you choose to remain set in “the old ways”, it could lead to irreversible health effects for your horse. Here are our 11 simple rules to follow. We’ve compiled these based on current scientific research in the field of equine parasitology. This research has highlighted the fact that equine parasites have evolved over the last few decades and it’s time that worming practices evolve too.

1. Perform 2-4 fecal egg counts in the first year to determine how many parasite eggs your horse is shedding. A horse’s shedding status dictates how frequently they should be dewormed. Once you have tested a mature horse several times to determine if they are a low, moderate or high shedder, their classification is unlikely to change unless their management significantly changes. ALL horses should be dewormed at least 1-2 times per year with a compound to target encysted cyathostomes (moxidectin) and tapeworms (praziquantel).

2. Understand what resistance is. Resistance is the ability of worms to survive following the administration of a dewormer which was previously able to kill them. Studies in Australia have shown that ascarids (roundworms) have developed a resistance to macrocyclic lactones (ivermectin). Pinworms are also showing some resistance to ivermectin. Small strongyles (the parasite of greatest concern in horses) is resistant to 2 out of 3 classes of drugs and is also showing emerging resistance to ivermectin and moxidectin.

3. Horses that are low shedders and are in good health typically only need 1-2 deworming treatments in the autumn and/or spring. Rotational deworming is AN OLD AND OUTDATED PRACTICE. Targeted deworming based on fecal egg counts and tailored to your horse IS RECOMMENDED.

4. There is NO broad-spectrum, “umbrella-type” dewormer we can give anymore and be sure it covers everything. It is quite concerning the amount of misinformation that is being to peddled to horse owners regarding what to deworm their horse with. Most of this information is not only incorrect and out-dated but could potentially threaten the health of your horse. Please contact us if you have any questions about deworming your horse.

5. Pregnant mares should receive a dewormer 2-4 weeks from their foaling down date. Foals should receive their first deworming at 12 weeks. We recommend using Strategy-T for their first worming.

6. Ascarids are commonly seen in young horses. The issue of widespread resistance of ascarids to ivermectin was previously discussed. This means that it is no longer recommended to deworm your foal with an ivermectin based wormer. We recommend foals are dewormed with either Strategy-T (oxfenbendazole/ pyrantle) or Equimax Elevation (which includes pyrantel and praziquantel in addition to ivermectin).

7. Tapeworms are best targeted at the end of the grazing season in late autumn/early winter. Fecal egg counts do not test for tapeworm and we recommend deworming for them regardless of your horse’s classification. Choose a dewormer which includes praziquantel – the compound effective against tapeworms. If you notice bot eggs on your horse’s legs – usually in autumn, it’s a good time to administer a dewormer which targets these parasites. We recommend using an Equest + Tape (moxidectin + praziquantel) at end of autumn/beginning of winter.

8. Competition horses or those that are being transported usually require more frequent deworming. This is not because their parasite burden has increased but may be due to the stress of training. This means the parasites they already have may begin producing more eggs. Perform a fecal egg count and adjust their management practices appropriately.

9. Pinworms are literally a pain in the butt for both horses and owners. Horses with a pinworm infestation typically rub their bottoms on trees, fences etc. resulting in hair loss and irritation at the base of their tail. The life cycle of pinworms is very long compared to other worms making them difficult to treat. We recommend deworming with a pyrantel based dewormer and disinfecting anywhere your horse may have rubbed its tail (fences, walls, feed bins) wash rugs with disinfectant clean their bottoms several times a day with disposable wipes. If that still does not work, you vet may be able to recommend an “off-label” deworming protocol. Check out our Factsheet : Pinworms.

10. Environmental management and manure collection is very important to help decrease the parasite burden on pasture and prevent re-infection in grazing animals. Pick manure up at least 2-3 times a week, if not daily. This is especially important on irrigated pasture. Practice rotational grazing and cross graze with different species (sheep or cows) if possible.

11. If your horse is at an agistment center who insists on deworming all horses with the same wormer at the same time, please have them contact us so we can best advise them on a parasite surveillance program. We have worked with numerous agistment centres who are proactive and who understand the catastrophic health issues that resistant parasites are going to cause to the horses in their care. Remember, a parasite population is shared between all horses on the agistment center but it does NOT mean that all horses have identical deworming needs.

Remember, Targeted Equine Deworming (TED) starts with a simple test – a Fecal Egg Count.

At our practice, we process fecal egg count samples from all over Australia for just $15 per sample. Access our
FREE Fecal Egg Count Starter Guide today!

Dr Tania Sundra BSc.(Hons) BVMS MANZCVS (Equine Medicine) is the practice owner of Avon Ridge Equine Veterinary Services. She is also a member of the Australian Equine Parasitology Advisory Panel which is in the process of developing specific worm management guidelines for horse owners in Australia.