Diagnostic-led worm control is where testing is used to tell you when your horse needs deworming. Blood or saliva testing should be conducted every six months to detect tapeworm burdens, preferably during spring and autumn. Faecal egg count (FEC) analysis should be carried out for assessing redworm and roundworm egg shedding throughout March to October for detection of adults. The small redworm blood test (which detects encysted larval phases) should be used from September to December, but if this is missed, testing should still be considered until April.


Additional factors to consider


Please note, these illustrations are simplified examples to demonstrate the effect of worm control strategies. Reducing worm life cycles occurring in horses and the paddocks they graze can take time before improvements in worm infection levels are seen.


Correct pasture management


As well as correctly managing worm burden levels within horses as described in the illustrations above, it is important to manage worm life cycles occurring on the grazing too. Good pasture management can reduce the need for dewormer use which will in turn slow the emergence of resistance.


A simplified version of a generic worm life cycle can be seen above, where the effect of dung removal on worm life cycles is illustrated. By removing dung, there is a significant reduction in eggs contaminating the grazing therefore limiting the number of infective larvae accessible for the horse to ingest.


To ensure your grazing has a low level of infective worm larvae, dung should be removed every 1-2 days, but twice a week may be suitable providing beetles and birds are not spreading the dung. It may be beneficial to keep horses on manageable sized paddocks to make dung removal more feasible and rotation of paddocks prevents grass from becoming overgrazed. If possible, it is important to completely remove the dung from paddocks and avoid harrowing to break up the dung. Harrowing practices simply spread the worm eggs/larvae throughout the grazing as most UK weather conditions are not hot or dry enough to eliminate worm eggs/larvae.


Conducting regular testing (as described below) will indicate how successful your paddock management is. If horses continually have test results indicating high infection levels, then there could be scope to make further improvements to your paddock management.


A suitable testing programme for most adult horses in the UK is illustrated on the right.


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New horses arriving at a yard should be kept separate from the rest of the herd for at least 3 days aſter treatment with a moxidectin/praziquantel combination dewormer. This practice will reduce contamination of your grazing with additional worm eggs. Testing prior to this treatment would inform you of the horse’s infection levels and whether additional testing or treatment may be required before the rest of the herd’s routine testing is due.


Underdosing should be avoided at all costs as the risk of developing worm resistance is increased due to worms being exposed to the drug without being killed. Ensure that you are using the correct dewormer dosage by using a weighbridge to determine the horse’s weight. And always administer deworming paste on clean flooring where possible so that any paste spat out can be re-administered.


Don’t leave worm control to chance, speak to your veterinarian or SQP to find out more on how to conduct appropriate testing for diagnostic-led worm control for your horse.


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