Vets say “paradigm shift” in horse deworming attitudes needed

The commonest types of worms that infect equids are the small strongyles (also known as cyathostomins).
The commonest types of worms that infect equids are the small strongyles (also known as cyathostomins).

A group of British equine veterinarians says an anthelmintic resistance disaster is looming unless horse owners radically change their ways.

In a letter to the journal Veterinary Record, David Rendle and colleagues from the British Equine Veterinary Association (BEVA) anthelmintic working group reported the findings of a small-scale survey into the use of fecal worm egg counts (FWECs) and anthelmintic sales.

The seriousness of the problem is highlighted by the fact that resistance to all currently available classes of anthelmintics has been reported in both the cyathostomins (small redworm) and ascarids (large roundworm). Furthermore, there is currently no prospect of new drugs in the pipeline.

The BEVA working group collected data on fecal worm egg counts performed and the sales of anthelmintic doses in the United Kingdom from 2015 to 2018.

They found that the number of FWECs performed increased by 29% (from 91,769 in 2015, to 119,030 in 2018).

The number of horse doses of anthelmintic fell by 2.9% over the same period, from 1,166,053 in 2015 to 1,131,759 in 2018 (in fact falling by 8% between 2015 and 2016, before gradually increasing each year after that).

Although it is encouraging that the number of FWEC tests performed has increased, the authors express concern at the low number of tests relative to the number of doses sold, and the increase in anthelmintic sales between 2016 and 2018.

They point out that if current guidelines were followed, and anthelmintic treatment carried out only when shown to be necessary by a FWEC, then there should be at least twice as many FWECs than anthelmintic doses. But the data showed that only one FWEC was carried out for every 11 doses sold.

They were also concerned that sales of the macrocyclic lactone moxidectin remained high throughout the four years. This was “despite universal consensus by experts that it should not be used as a routine treatment”.

They conclude: “If a crisis in equine welfare is to be averted, then a paradigm shift in attitudes to anthelmintic use and a radical change in the availability of anthelmintics will be required.”

Anthelmintic resistance in equids. David Rendle, David Mountford, Colin Roberts, Roly Owers, Tim Mair, Mark Bowen, Jacqui Matthews, Iain Richards, Jane Hodgkinson, Tamzin Furtado, Laura Sharpe, and Richard Frost. Vet Record (2021) 188, 230

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