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ES Insulin dysregulation in horses: a new epidemic or a new perspective?
March 7, 2025
It is a routine deeply ingrained in many horse owners: deworming as soon as spring arrives. “Better safe than sorry,” goes the saying. But is that still correct?
The modern parasite approach says otherwise.
In the past, deworming was done according to fixed schedules. Nowadays, it is known that blind deworming can lead to the development of resistance in worms. It is therefore essential to first perform fecal examination before proceeding with deworming
Development of resistance: dewormers are losing their effectiveness.
Disrupted gut flora: with consequences for digestion and immune balance.
Unnecessary tax: the liver, intestinal wall and entire metabolism are burdened.
An often forgotten aspect of deworming is that not every dewormer works against every worm.
Yet in practice, “something is often just pulled off the shelf” — without taking into account:
the type worm (e.g., large strongyles, small strongyles, roundworms, tapeworms, pinworms)
from life cycle phase (eggs, larvae, adult worms)
from time of the year
from product effectiveness at that specific horse or company
❗ Many dewormers work not effective against larval stages of small strongyles — precisely the group responsible for severe intestinal problems and resistance.
On top of that, research (Matthews, 2008; Nielsen et al., 2020) shows that:
Resistance to benzimidazoles (such as fenbendazole) is widespread
Roundworms in young horses develop resistance to ivermectin
Many horse owners not knowing which remedy they used when — or why
Young horses (<3 years) have not yet built up a stable immunity against gastrointestinal parasites. For this group, more frequent deworming is sometimes necessary – but here, too, fecal egg counts help to better tailor risks and schedules.
Blind deworming is outdated. Guidelines based on EPG, as described by Nielsen et al. (2020) and Matthews (2008), clearly demonstrate that resistance can be prevented with risk-based treatment. In Belgium, too, this is the starting point of practice-oriented systems such as Wormiscope.
Young horses (<3 years) have not yet built up a stable immunity against gastrointestinal parasites. For this group, more frequent deworming is sometimes necessary – but here, too, fecal egg counts help to better tailor risks and schedules.
For adult horses, the following applies: 3 to 4 times a year, spread over the grazing season.
Younger animals (<3 years) need checks more often.
After deworming, it is also useful to later reduction test to be done to check whether the remedy was effective. The period within which this must be done depends on the deworming product used.
Deworming before the grazing season is not a given — unless fecal egg counts show that it is necessary.
Not the calendar, but the lab results determine what is wise.