DEWORMING YOUR HORSE“what to use & when…is it necessary  at all?”

Horse Care:  Part 2

Equine worms (endoparasites) have been recognised as the cause of disease in horses since the rise of the Roman Empire.  Clinical manifestations of a worm infestation are variable and can range from relatively asymptomatic, to poor growth or performance through to weight loss, scouring, colic, coughing, and death.  Other less dramatic symptoms include tail rubbing and mild ill thrift.

The most important worms that infest horses to cause clinical disease are the large strongyles (large red worms), small strongyles or cyathostomins (small red worms), threadworms and large roundworms.  Other worms of lesser pathological significance are tapeworms and bots.  Indiscriminate rotational deworming protocols are responsible for the resistance reported in many worm species, and especially the small strongyles (cyathostomins) which are of a significant concern in adult horses, and the large roundworm, Parascaris equorum, which remains the most important parasite infecting foals and weanlings.

Horses are infested with worms by ingesting infective larvae from the pasture.  Adult worms survive within the horse’s intestines and produce eggs that are passed into the environment within the droppings.  Dependant upon temperature and moisture, the eggs will hatch and develop into infective larvae.  The rate at which the eggs hatch and larvae develop is influenced by environmental and climatic conditions with high numbers developing in warm moist conditions and smaller numbers developing when conditions are cool and dry.  Pasture contamination and egg / larva survival are influenced by climatic conditions with an increase survival time in cool weather with adequate moisture, whilst a reduction in egg and larvae numbers is seen in hot and dry conditions.

Effective worm control programs comprise reducing (or an attempt to eliminate) the worm population from the herd (of horses), limiting reinfestation by removing manure, harrowing the pasture, grazing management and monitoring worm burdens via worm egg counts.

Rotational Deworming your horse consist protocols consisting of regular (every 8 weeks) anthelmintic administration to all horses is the traditional treatment that is aimed at eliminating adult worms and this has successfully controlled the large strongyles, but it is also responsible for the emergence of equine worm resistance.  Anthelmintic resistance is recognised to be a growing threat to worm control and equine health.

Targeted and/or Selective Deworming your horse, aim to prevent parasitic disease by minimising pasture contamination and preservation of refugia.   Parasitic refugia is the worm population present in those horses that are not selected for anthelmintic treatment.  The goal of this method is to provide a pool of genes within the worm population that remains susceptible to dewormers, thus diluting the frequency of resistant genes.    This strategy has been devised for the control of small strongyles in adult horses.

What & When to deworm: Strategic Deworming Programs are sophisticated protocols that are formulated to protect your horse from parasite related disease, whilst reducing parasite numbers on the pasture, preserving the effectiveness of current anthelmintic drugs and most importantly reducing the emergence of resistant worms.  Your horse vet can be of great assistance in formulating an appropriate strategic deworming protocol for your horse’s individual circumstance by taking the following factors into consideration:

  1. Stocking density and frequency of change in the horse population;
  2. Environmental and climatic influences;
  3. Results of WORM EGG COUNTS;
  4. Life cycle and seasonal influences of specific parasites;
  5. Pasture management including paddock rotation, manure removal and cross grazing with other species.
  6. Collective deworming of all horses on the property with the same drug and at the same time;
  7. Use of an effective anthelmintic medication specifically used in accordance with the results of the Worm Egg Count.
  8. Alternating/Rotating anthelmintic drugs on a seasonal basis.

Effective Anthelmintic drugs:

  1. Benzimidazoles – Fenbendazole, Oxfendazole & Oxibendazoles
  • eg. Panacur, Systamex, Strategy-T
  • effective against larval and adult roundworms, they are not effective against tapeworms and bots and resistance have been reported.
  1. Macrocylic Lactones – Abamectin, Ivermectin & Moxidectin
  • eg. Promectin, Noromectin, Equest
  • effective against a wide variety of roundworms and bots, they are not effective against tapeworms.
  1. Praziquantel – Praziquantel
  • eg. Equimax, Equest Plus
  • only effective against tapeworms and the drug of choice for tapeworms in horses.
  1. Tetrahydraprimadines – Pyrantel and Morantel
  • eg. Strategy-T, Ammo
  • effective against larval and adult roundworms and tapeworms.

Is Regular Deworming your horse necessary? Without doubt deworming is a very important practice necessary to promote horse health.   However, the frequent and haphazard manner by which traditional deworming programs (rotational programs) have been applied is wholly out-dated and responsible for the disturbing emergence of worm resistance.    A Strategic Deworming protocol will determine the minimum number of deworming treatments required per year in conjunction with use of the most effective and season appropriate active.  Furthermore, this method will ensure that the correct dose is administered and best management practices are applied in order to protect the horse from parasite related diseases.

If you would like to conduct a Worm Egg Count (WEC) for your property, Dawbuts in Camden NSW conduct diagnostic testing.

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