A comprehensive control program for gastrointestinal parasites in horses requires a three-pronged approach:

  1. Environmental management
  2. Strategic deworming
  3. Monitoring of parasite load

Environmental management

Removal of feces from horse’s pasture has been shown to be as effective as the use of dewormers alone in minimizing pasture larval counts.

Managing pastures:

  • If possible, rotate pastures
  • Remove intact fecal balls (where the parasites develop) at least twice per week
  • Avoid high stocking rates (one horse per two acres is an ideal maximum)
  • Young horses are more susceptible to GI parasites (give them the cleanest pasture)

Managing stalls:

  • Infection with some parasites (ascarids, pinworms) can occur in the stall i.e., without pasture access; this is of special concern for the neonatal and suckling foal
  • Foals will rapidly pick up infection as they investigate (lick) their surroundings
  • Thoroughly clean walls and utensils
  • Use clean bedding
  • Keep the mare clean

Strategic deworming

Deworming as the sole means of controlling GI parasites is inadequate on a long-term basis. This is mainly due to the development of resistance. Dewormers should be regarded as only one component of a GI parasite control program.

  • Start in April (prior to first turnout).
  • Don’t rotate dewomers frequently. Use compounds in the same anthelmintic class (i.e., macrocyclic lactones, benzimadazoles or pyrantel) for 1 to 2 years before changing. Rotating dewormers frequently probably encourages resistance against multiple classes.
  • During the summer months, watch for development of drug resistance in foals and adult horses by monitoring annual fecal egg counts both before and after deworming.
  • The strategy recommended by the Ontario Veterinary College for use in Ontario is a program in which you deworm adult horses for the first 4 months of the grazing season, plus administer an early winter treatment to minimize overwintering cyathostome burdens and remove bots.

3 Strategic Deworming Options

Option #1

Benzimidazoles and pyrantel salts (Panacure, Safe-Guard, Strongid, Exodus).

What to do?
Deworm at monthly intervals through to July.


Ivermectin (Eqvalan, Equell, Equimax, etc.)

What to do?
Deworm every two months through to July.


Ivermectin (Eqvalan, Equell, Equimax, etc.)

What to do?
• Do not give to horses less than 2 months of age.
• Moxidectin can depress egg counts for up to three months.
• Treat once at first turnout (April), then treat just once more in November.v


If treatment for tapeworms is required, deworm in the fall using either:

  1. Pyrantel (Strongid): double the standard dose, or
  2. Praziquantel (Quest Plus, Equalan Gold)


Allossery Equine Veterinary Services
11499 York Durham Line
Mount Albert, Ontario
L0G 1M0

(289) 338-2068