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  What active ingredient controls what
  When to worm
with what
  Pregnant mares, foals and new horses
  Rotation
  Resistance

Treatments for different parasites/parasitic stages are required at different times of the year. Programmes are based on the routine control of roundworms, with additional strategic treatments at specific times of the year for the control of

 
tapeworm, bots and most importantly
encysted small redworm.

Illustrated below is a guide to when to
worm and with what.
       
MAR APR MAY JUN JUL AUG SEP OCT NOV DEC JAN FEB
ROUTINE CONTROL
ROUNDWORMS - Routine roundworm control throughout the grazing season. However with milder and wetter winters, horses are at risk of picking up infective larvae late in the year (Love S, 2003), as such routine roundworm control should be undertaken throughout the year. Small redworm are now the most common and harmful parasite to affect horses (Love S et al, 1999). Ingested while the horse grazes, the larvae can cause life-threatening illness due to the invasion and build up of larvae in the horse’s gut wall. In addition, although the widespread use of modern wormers has reduced the number of large redworms, the migratory larval stage of the large redworm remains potentially fatal.
Routine Treatment (all year round):
moxidectin every 13 weeks,
or ivermectin every 8-10 weeks,
or pyrantel(A) every 4-8 weeks,
or fenbendazole(B) every 6-8 weeks,
or mebendazole(B)(C) every 6 weeks.
STRATEGIC TREATMENTS
ENCYSTED SMALL REDWORMS - Hidden in the gut wall the encysted small redworm if left untreated typically emerge en-masse in late winter/early spring.
                Strategic
Treatment
(Nov):
Single
dose of
moxidectin
based
wormer
or 5-day
course of
fenben
-dazole (D)		     Strategic Treatment (Feb):
Single dose of moxidectin based wormer or 5-day course of fenben-dazole (D)
TAPEWORMS - Exposure to tapeworm is greater during periods of prolonged grazing, as such treatment should be undertaken in the autumn following summer turnout to pasture. Treatment for tapeworm is recommended every 6 months (Proudman C, 1994).
Strategic Treatment
(Mar, Apr or May):
Single dose of praziquantel-based wormer or double dose of a pyrantel-based wormer.		       Strategic Treatment
(Sept, Oct or Nov):
Single dose of praziquantel-based wormer or double dose of a pyrantel-based wormer.		      
BOTS - Treatment recommended in the late autumn/early winter prior to larvae maturing in the spring.
                Strategic Treatment
(Nov or Dec or Jan):
Single dose of moxidectin- or ivermectin-based wormer after the first frost.		  
     
    (A) Pyrantel-based wormers only control adult worms and have no activity against larvae. Plus with large and small
      redworm resistance to pyrantel-based wormers, their use as routine wormers may be inappropriate and should
      only be used after consultation with your vet.

(B) With widespread small redworm resistance to fenbendazole and mebendazole-based wormers, use of these as
      routine wormers may be inappropriate and should only be used after consultation with your vet.

(C) Mebendazole-based wormers have no activity against the migratory larvae of large redworm.

(D) 5-day treatment not recommended if benzimidazole-resistant strains present (Coles G et al, 2003).

     
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