As we settle into the new year, many horse owners will be required to worm their horses in line with their yard schedule – often, this involves horses being chemically wormed regularly, regardless of their individual worm burden. Wormers of various descriptions have been in use since the mid-to late-90s (Potter, 2012) to control worm burdens in the horse, though the more recent school of thought is in favour of taking a more horse-centred approach.
At this time of year, horses are often wormed for tapeworm and roundworm. Lightbody et al (2016) found that almost 60% of the horses sampled had a tapeworm burden, although horses do not need worming for tapeworm unless they have a moderate–high burden (Kjaer et al, 2007). Roundworm infestations are more common in foals and horses under 2 years of age (Reinemeyer, 2009), and have been found in 31–61% of foals younger than a year old (Wilson, 2011). Treatment of both of these worms can be targeted with products containing praziquantel or an elevated dose of pyrantel (Reinemeyer et al, 2006; Slocombe et al, 2007).
When using the traditional method of blanket worming, all horses on a property are wormed for the same parasites at the same time. Research has shown that anthelmintic resistance is common in equine parasites (Brady and Nichols, 2009; Nielsen et al, 2014; Cai et al, 2024), so horse owners should be encouraged to test their horses for any worm burden and then only worm if their horse has a problematic worm burden. Methods for testing whether a horse has a worm burden include saliva tests, blood tests and faecal egg counts. Blood tests for tapeworm must be performed by a veterinarian, but saliva tests and faecal samples can be collected by the horse owner before being sent off for testing. Using tests to determine whether each horse has a worm burden before treating can be logistically challenging, especially on larger yards, but will ensure that horses are not unnecessarily wormed. Limiting the use of chemical wormers will help slow down the progression of anthelmintic resistance, ensuring that current wormers remain effective in the future (Rendle et al, 2024).
It is well-known among the veterinary profession that traditional methods of worming no longer serve the equine community very well. Although it may require an initial adjustment period for livery yards to change from blanket worming to a more individual approach, the multiple benefits speak for themselves. Veterinarians should, where possible, encourage decision makers (be they yard managers or yard owners) to move to individual worming programmes. The growing body of evidence to support this should go a long way to help bring about change to more modern worming practices.