Worm Control

Anthelmintic or wormer resistance is an increasing problem which we ignore at our peril. The days of blanket internal worming are over. Below is a worm control guide to help horse owners plan their worming regime, please discuss the programme and its relevance to your situation with your veterinary surgeon.

Control involves three approaches:

  1. Effective pasture management
  2. Identifying and monitoring horses with significant worm burden
  3. Using effective anthelmintic (wormer) treatment.

Pasture management

Remove droppings from pasture at least once every two weeks. Use adequate grazing densities – overcrowding promotes grazing roughs where horses do droppings.

Identifying and monitoring horses with significant worm burden.

Worm egg count (WEC) is the basis for identifying these horses. Fresh droppings should be collected in airtight bags, kept cool and delivered the same day to the surgery.

Horses with low or zero WEC should be tested every 4 months. Horses with significant WEC should be treated and re tested in 2-3months. Horses with high burdens (more than 1000 eggs per gram) should be tested again following treatment to check for resistance.


Worm egg counts are not reliable for Tapeworm. ELISA blood test in spring and treat as required. Treat once or twice yearly (spring and autumn) depending on blood results.

Chemical Treatments (Anthelmintics)

Horses with high worm egg counts – use Ivermectin or Praziquantel. Moxidectin is highly effective and should be reserved for annual encysted small Redworm (cyathostomes), new horses and those with resistance to other wormers.

Beware of:

  • Under dosing due to poor weight estimation
  • Under dosing due to horse spitting out wormer
  • Resistance in worm population.


Worm Control Programme

Pasture management – collect droppings at least once per fortnight.

March/April - ELISA blood test for Tapeworm

  • Negative / low result – treat in Sept/Oct (see below)
  • Positive / high result – treat immediately with Praziquental or Pyrantel

March/April – Worm Egg Count

  • Low result - test again in 3 months
  • High result - treat with Ivermectin or Moxidectin, retest after 8 weeks

July - Worm Egg Count

  • Low result - test again in 3 months
  • High result - treat with Ivermectin or Moxidectin, retest after 8 weeks.

September / October - treat for Tapeworm and Redworm larvae (Moxidectin and Praziquantel).

New horses - treat with Moxidectin and Praziquantel on arrival.

After treatment - horses should be kept stabled for 48 hours to allow eggs to be evacuated.

Pasture rotation should not take place within 2 weeks after treatment.


Chemical Family Active Ingredients Wormer Name
Benzimidazole Fenbendazole Panacur, Panacur Equine Guard.
Macrocyclic lactones Ivermectin Eqvalan, Vectin, Eraquell, Animec, Noromectin,Bimectin, Maximectin
Macrocyclic lactones Moxidectin Equest
Pyrimidine Pyrantel Strongid P, Pyratape P, Exodus, Embotape
Quinolone derivative Praziquantel Equitape
Combination Ivermectivn and Praziquantel Eqvalan Duo, Equimax
Combination Moxidectin and Praziquantel Equest Pramox


Anthelmintic Foals Pregnant Mares Lactating Mares
Fenbendazole Yes - any age Yes Yes
Pyrantel > 4 weeks Yes Yes
Ivermectin > 0-8 weeks
(* products vary)
Yes * Yes *
Moxidectin > 4 months Yes Yes
Praziquantel > 2 months Yes Yes
Ivermectin/Praziquantel > 2 weeks to 2 months * Yes * Yes *
Moxidectin/Praziquantel > 6.5 months Yes Yes



Scott Dunn’s Equine Clinic is part of CVS (UK) Limited, a company which owns over 300 veterinary practices in the UK. Company Registration Number 03777473. Registered Office CVS House, Owen Road, Diss, Norfolk, IP22 4ER