By Dr. Carolyn Walsh
Williams Lake Veterinary Hospital

Fall is an essential time to deworm horses as they may have ingested parasites during the grazing season. Among these parasites are tapeworms, strongyles and bots. 

All of these parasites can cause colic, and should be given special attention in the fall. The best way to protect against all of these parasites is to use a broad-spectrum dewormer such as ivermectin or moxidectin with praziquantel.   Through the summer months, different deworming products can be used strategically, depending on the fecal egg counts, pasture stocking density and pasture management.

Fecal Egg Counts: Fecal egg counts can help you plan your overall parasite-control program and monitor how well it is working.  As the name implies, these tests determine the concentration of parasite eggs in manure. Collect a fresh sample and submit it to the veterinary hospital.  A veterinarian will evaluate the fecal egg count and consult with you regarding your deworming program.

Some horses are 'heavy shedders', while others are 'light shedders'.  Horses who are heavy egg shedders should be dewormed more frequently through the summer months, where light shedders can be dewormed less frequently.  Strategic deworming will help to both reduce the pasture contamination, and decrease parasite resistance to deworming products by minimizing their use.

Bots: Bots are fly larvae.  The botfly lays eggs around the face and legs of the horse.  The horse licks his legs, eggs are ingested, and the larvae migrate and attach to stomach wall, where they develop and cause irritation.  The first hard fall frost kills bot flies, and moxidectin and ivermectin are the only products effective against bots.

Tapeworms: It is advised to deworm for tapeworms at least once a year, as they can be a significant cause of colic.  Deworming with a product containing praziquantel will eliminate tapeworms.  Be aware that horses infested with tapeworms will only show positive fecal egg counts in one out of 6 fecal floats.

Strongyles: Strongyles are the most common equine parasite, and they can also be a significant cause of colic in horses.  Most products are effective against strongyles to varying degrees.  Fecal egg counts are an excellent way to evaluate the dewormers’ effectiveness/ resistance, as well giving an indication for the frequency of strategic deworming needed for each individual horse.

Tip:  To be sure that the dewormer gets to the worms and does its job, you’ll need to make sure your horse’s mouth is clean (free of hay/feed) before administering the paste.

If the horse is very young or very old, or has not been dewormed in over a year, you should consult with your veterinarian before deworming.

As your horse goes into the winter season you will want to ensure he is in good condition.  If the ribs are easily felt or are visible, have his teeth checked (have the teeth been floated within the last 1 – 2years?), review your deworming practices, and have him examined for underlying disease. 

Older horses may need to be fed supplements and wear blankets through the winter to maintain their condition.

For further information please see the following link:  http://www.aaep.org/health_articles_view.php?id=125

For more information, please contact your veterinarian.