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Less frequent but targeted worming could help prevent welfare ‘catastrophe’

More evidence has emerged to indicate that reducing worming frequency does not typically have a negative effect on horses’ health, and may help prevent an “equine welfare crisis”.

Leading equine parasitologist Martin Nielsen’s research supports the move away from the traditional approach, of frequent worming without diagnostic testing.

Dr Nielsen’s study involved 99 mares and 93 foals at stud farms in New Zealand. Researchers evaluated the worm egg counts, weight and health of groups of horses under different parasite control programmes.

They found no significant difference in egg counts between the mares wormed routinely at different set intervals, and those only wormed when counts exceeded a certain level. The foals who were wormed at two and five months old had significantly more ascarid (roundworm) and strongyle (redworm) eggs than those wormed monthly with alternate products, but all the horses were healthy.

“De-worming every six to eight weeks and rotating between products is still very common around the world but this sort of carpet-bombing is completely unnecessary and drug rotation does not prevent drug resistance,” Dr Nielsen said, adding that the persistent and growing resistance to the anti-parasitic drugs available to horse owners is “challenging us to find more sustainable and yet effective parasite control programmes”.

“Many people are not comfortable with de-worming less frequently, thinking it will compromise horse health, but our study shows that this is not the case; no adverse health effects were seen that could be ascribed to scaling down de-worming intensity.”

Dr Nielsen told H&H the aim of any worming programme should not be to eradicate worms, but to reduce the risk of parasitic disease, and that it is natural for horses to have worms.

“The worms are supposed to be there, just like horses also harbour lots of bacteria in their intestinal tracts – yet we don’t go around treating them with antibiotics all the time,” he said. “This study demonstrated that all horses (foals as well as mares) were healthy, and no differences were observed between the groups during the study. And that is what matters.

“Just treating at fixed and frequent intervals with no testing is the equivalent of fumbling in the dark. You will have no idea of what you are doing.”

Dr Nielsen has created videos on the subject, one for vets and one for owners, above, which the British Equine Veterinary Association (BEVA) is sharing to help spread the word.

BEVA health and medicines committee chairman David Rendle said: “This study provides further evidence to show that there is no justification for the traditional approach of calendar-based routine treatment and gives further reassurance that the frequency of treatment can be reduced without detriment to equine health or development of youngstock.

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“Spreading this information will hopefully encourage any horse owners who have not done so already to change from their old-fashioned habits of frequent de-worming to a diagnostic test-led, or at least a more strategic approach with routine drug-resistance testing.

“In so doing we can help avert the potential equine welfare crisis that all are agreed will inevitably ensue if the equine industry continues with the indiscriminate use of anthelmintics [de-wormers]. I would urge anyone who has not discussed worming with their vets recently to do so before the spring.”

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