Horse Worms, A Guide to Spring Worming
Written by Caroline George BVMS MRCVS, Lambourn Equine Vets
Topic – Horse worms and Spring Worming
Here Caroline George BVMS MRCVS from Lambourn Equine Vets takes a look at the different types of spring worms, the importance of spring worm control and the Intelligent Worming Programme.
With Spring approaching our thoughts turn to worming our horses. There are a variety of endoparasites “worms” which infect horses in the UK, the majority of which are carried with minimal harm to the adult horse. There are however, certain horse worms which in low numbers are unlikely to cause harm, but can lead to problems when a larger burden is established. When the population of worms carried by a horse becomes greater than a certain threshold this leads to clinical signs which can have devastating consequences such as colic or lead to a more chronic ill thrift. The two most significant worms we manage are cyathostomes “red worms” and anoplocephala “tapeworms”.
Spring and Worm Control
Spring is an important time for horse worm control as whilst the breeding cycle is dormant during the cold winter month’s the increase in temperature in the spring leads to recrudescence of larvae and recommencement of the worms breeding cycle. Larval emergence in the spring and the increase in a horse’s burden can be detected by testing the faeces to confirm the presence of eggs. The threshold for a significant red worm burden in horses is 200 eggs per gram and a burden above this level will need targeted treatment. Tapeworms also begin to cycle at this time of year, a blood test is available to monitor antibodies to tapeworms which identifies exposure. Recently a commercially available test for tapeworm burden using a sample of your horses’ saliva has become available however, at present these still have limited published scientific data to substantiate it at present.
Intelligent Worming Programme
With a limited number of wormers available for treatment of worms in horses wherever possible an “intelligent” targeted worming (IWP) approach should be taken to avoid increased resistance to the wormers available. It is critical to remove your horses’ droppings from their paddocks frequently to reduce the risk of ongoing exposure and reduce the risk of resistance developing. Worming horses unnecessarily kills only the worms sensitive to the product used, any resistant worms will survive, if this continues the number of horse worms sensitive to the product decreases leaving a burden in the horse.
It is critical to remove your horses’ droppings from their paddocks frequently to reduce the risk of ongoing exposure and reduce the risk of resistance developing
Evidence has shown that only 20% of horses carry a significant burden requiring treatment. An IWP involves testing the droppings of your horses and only treating the horses with significant burdens followed by retesting to confirm effective treatment using an Egg Worm Count Kit. Tests should be carried out in the spring, summer and autumn each year. With the absence of a definite test for active burden of tapeworms treatment for this should be undertaken in the spring using praziquantel or a double dose of pyrantel. Likewise the presence of encysted red worm larvae can’t be tested therefore an autumn treatment for encysted cyathostomes using a product containing moxidectin is most likely to be effective.
Youngstock and Broodmares
IWP is recommended for the majority of horses but does require set stocked fields and regular poo picking. Whilst monitoring cyathostome burden in young stock and broodmares is valuable their immune system is less able to cope with horse worms and therefore will require more regular analysis. Analysis is ideally required on a fortnightly basis and with a specific worming programme drawn up as in addition they are also more susceptible to other worms. Treatment for Parascaris equorum (roundworm) using ivermectin or pyrantel and Strongyloides Westeri (Threadworm) using ivermectin should be considered.
Careful choice of a worming programme to suit your situation and stock in conjunction with your veterinary surgeon should be evaluated each year to ensure your horses are managed effectively with resistance avoided and monitored.
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