Deworming

All horses have parasites. In order to prevent your horse from having a parasite related problem it is important to have a deworming routine that your following in addition to pasture management.

The most common parasite related problems are colic, diarrhoea, or weight loss. Lung and skin problems can also occur with certain types of parasites. See below for the different types of parasites.

It is better to guard against than treat the resulting problems. Please be aware though that some parasites have developed resistance against some of the anti-parasitic medications available.

Management may include rotation of pastures to be used every other year by horses, and having separate pastures for winter and summer, and taking faecal samples to check for worm eggs.

In Sweden there are several different 'families' of dewormers:

Benzimidazole & probenzimidazoles: Fenbendazole, Febantel

Tetrahydropyramidines: Pyrantel pamoate

Macrolides: Ivermectin, Moxidectin

Praziquantel

Large Strongyles & Cyathostomes (small strongyles)

Horses are infected by larvae from the pasture. These burrow through the wall of the bowel and move up into the blood vessels of the small intestine. The most problems arise when this causes damage in the 'cranial mesenteric artery' which supplies a very large part of the intestines.

The worms have a stage which allows them to 'rest' in the intestinal wall, at which time it is very difficult to affect them.

Recommended deworming treatment -

Ivermectin containing preparations (e.g. Ivomec, Noromectin, Bimectin). These give an 8 weeks period before the horse will start to shed eggs again in the manure (ERP - egg reappearance perdio). Treat every 8 weeks.

Moxidectin containing preparation (e.g. Cydectin) Gives a 12 week ERP. Treat every 12 weeks. 

Pyrantel containing preparation (e.g. Banminth, Fyrantel) Gives a 4 week ERP. Treat every 4 - 5 weeks. 

Round worms - Ascarids

These are normally a problem in younger horses and foals, as older horses develop immunity although scarring in the bowel wall can sometimes be seen in older animals, likely a result of prior infection. 

The eggs are excreted in the manure, and persist in the environment for a long time as they are highly resistant to weather extremes.

It appears that a resistance against ivermectin based deworming medication is developing, and we have seen several cases of foals with large burdens of worms despite being very regularly wormed with these preparations. In such cases pasture management, regularly moving young mares and foals, so the number of worms they are exposed to is reduced in size, or a change of wormer. It may be wise to use a benzimidazol or pyrantel containing medication, however these only have a small effect against strongyles, so a combination may be needed.

If your foal does develop colic from these worms this can be very severe and the secondary complications with this problem lead to a very poor survival rate post surgery, only around 20%.

Recommended deworming treatment -

As above following deworming at  8 and 16 weeks of age. In addition at times a foal should be given  a benzimidazole containing preparation (e.g. Axilur, Flubenol) to protect against round worms. 

Contact your veterinarian if you horses have a history of this problem for further advice. 

Moxidectin should not be given to any foal younger than 16 weeks.

Tape worms:

The species that tends to affect horses (Anoplocephala perfoliata) mostly lives in the final part of the small intestine and the caecum (the appendix which is very large in the horse). Faecal analysis may produce false positives (not show the parasite in affected horses), and studies show that these are quite common in the Swedish Horse Population.

Worming against tapeworms should be performed once yearly, in the spring, or both the spring and autumn if your horses have had specific problems with tape worms.

Recommended deworming treatment::

Praziquantel (Droncit) - Normal dose, once a year, or twice if indicated

Pyrantel (Banminth or Fyrantel) - Double dose, once a year, or twice if indicated.

General advice:

Using faecal counts one can determine which particular paratises are a problem and how heavy the worm burden is in your horses. Older horses with small worm burdens may not need to be dewormed at all, but foals and young horses must be wormed regularly!

Stables:

All the horses in a stable should be wormed at the same time with the same preparation to reduce the potential for resistance development. 

New Horse:

Worm any new horse arriving on the property 3 days prior to being turned out, then worm along with all the other horses.