Horse Worming

It is normal for your horse to carry a small parasite burden. This is necessary for normal regulation of the immune system. No program will or should totally eliminate your horse's worm burden.

Currently the most important equine parasites are cyathostomes (small red worms) and tape worms. Cyathostomes spend part of their life cycle dormant in the hind gut, and can remain there for several years. At this stage drugs are relatively ineffective at killing the parasite.

PinwormVery few new worming drugs have become available in the last ten years, and it is inevitable that eventually resistance will develop to the drugs that are currently on sale. Indeed, there are already reports in the literature of resistance to benzimidazoles and invermectin. To prolong the useful life of these drugs, it is important that they are used correctly. Each yard is different and you should discuss your individual requirements with your veterinary surgeon.

There are a couple of rules to follow that will help reduce the likelihood of resistance developing on your premises, and help maintain your horse's parasite burden at a healthy level.

  • All horse's on the premises should follow the same program.
  • All horse's should be measured with a weight tape to obtain an accurate weight for dosing.
  • Regular removal of droppings from the pasture will significantly reduce the parasite challenge to your horse.
  • Co grazing with sheep and cattle will reduce the number of worm eggs on your pasture. Pasture should not be overgrazed.
  • New horses coming onto a yard should be wormed before turnout.

TapewormFaecal worm egg counts and tape worm ELISAs are tests that give an indication of a horse's level of infection, and should be performed on all horse's within a group. horses require to be dosed at certain times of the year with specific drugs. However 20% of horses within a group will shed 80% of worms, and so quarterly faecal worm egg counts (FWEC) can be used to determine which horses should be targeted for treatment during the remainder of the year. There is also an ELISA blood test that can be used yearly to detect evidence of tape worm infection. Faecal worm egg counts do not indicate the level of tape worm burden a horse may be carrying so this should be taken into account when planning a program for your horse.

It must be understood that FWEC do not detect encysted cyathostomes, and as no reliable test exists for this parasite.

FWEC can be used to isolate horses within a group that are producing high numbers of eggs, and these animals can be targeted with a suitable product whilst the other animals are left untreated, thus reducing the amount of wormer used and reducing the speed at which resistance is likely to occur.

Please contact an equine vet at the clinic to discuss your horses individual needs.