Mar 26 2015

Deworming Horses

Parasites are menacing culprits.  Severe infestations are capable of stealing valuable nutrition, damaging intestines and other tissue, and even killing horses.  The most challenging aspect is that intestinal worms cannot be totally eliminated, only controlled.  Adding to the problem is the fact that there are many types of parasites, and each seems to have its own unique way of attacking its host, your horse.

The worms of most concern are Nematodes or Roundworms.  These worms can be found in the large and small intestines as well as in the lungs.  Examples include Strongylus vulgaris and Cyathostomes.  St. vulgaris are considered major culprits associated with colic in horses.  These parasites interfere with blood flow to intestines leading to tissue damage.  Their occurrence and significance has dramatically decreased over the past 15 years, due to the common use of Ivermectins.  They develop all year round, with the fastest development occurring in the summer and fall.  Horses usually have them but show no clinical signs.  Cyathostomes or small strongyles live in the large intestine of horses.  They are most common in young horses during the winter months.  Clinical signs include profuse and chronic diarrhea, weight loss, depression, and fluid under skin.  Treatment is very difficult, therefore, prevention is key.

The other important class of worms includes Cestodes or Tapeworms.  These are moderately common in western Canada in horses that are managed in pens, paddocks and small pastures with a common feeding area, such as bale feeders.  Horses with these worms are 8 times more likely to suffer from spasmodic colic and 26 times more likely to encounter ileal (part of the small intestine) impaction.  Another class of intestinal parasites is Pin worms.  Pin worms are much less of a concern, with the only common clinical sign being scratching the bum.

Intestinal parasites do have ideal growing conditions.  They typically grow faster in humid conditions.  We also see faster parasite growth in the months with more consistent weather, in the summer and winter.  Parasites grow much slower when there is a fast and dramatic change in weather.

At Twin Valley Veterinary Health Services, we are recommending horses be dewormed twice a year.  This should be done in the spring and the fall of every year.  Deworm after the strong growing seasons with one of the listed drugs below.  We recommend that every horse on the premisese dewormed at the same time.  The three drugs that we recommend using are Ivermectin, Moxidectin and Praziquantel.  Ivermectin is the only drug that successfully treats Strongylus vulgaris, the round worm.  Moxidectin is the only drug that gets the juvenile form of small roundworms Cyathostomes.  Praziquantel is the drug of choice for the prevention and treatment of tapeworms.  Products that include these drugs are Eqvalan Plus (Ivermectin and Praziquantel) and Quest Plus (Moxidectin and Praziquantel).

If you have any questions regarding the above information or any questions/concerns in general, please contact Twin Valley VHS at 745-6642.

Dr. Justin Noble DVM

Twin Valley Veterinary Health Services

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