Drugs alone are nowhere near as efficient as good pasture management so it is essential to:
- Poo-pick regularly (twice a week).
- Ensure you are dosing wormers at the correct weight for your pony (otherwise all you will be doing is giving the worms a taster and creating drug resistance).
- Quarantine newcomers and treat with an appropriate drug (eg moxidectin).
- NEVER over-stock.
- Make use of ways to reduce worm burden on pasture – co-grazing with sheep or cattle (who eat the eggs off the pasture), or harrowing in the summer (not winter).
Type of drug use
There are three main ways you can use drugs, and each has its perks.
This is the classic style of regular use of anthelmintics (wormer) based on action time of drugs – ie dosing with moxidectin every 13 weeks (13 weeks is how long it takes for eggs to reappear in faeces after dosing – it varies for each drug). It is favoured by drug companies because you use a lot of product, and by yard owners because it is easy to follow and you feel reassured that you are actively treating for worms. However, doing it this way you are using a lot of wormer on horses that don’t need it (fact: 20% of horses carry 80% of the worms) which costs a lot of money, and this “over-worming” is the biggest factor in creating drugs resistance. If you aren’t careful you wind up spending lots of money dosing your horses with a drug that isn’t working, because you have always used that drug and the worms are resistant to it.
This allows us to treat our horses only at the most appropriate times by using the knowledge we have about the worms’ life-cycle to predict when worm burdens will be highest (and treating throughout that time). For example treating encysted cyathastomes over winter. This is more rational than blindly treating based on drug action and there is less risk of drug resistance. However you can run into problems if there are unpredicted weather patterns (which seem to be a regular occurrence now) or if animals with a heavy worm burden are added to the pasture.
Targeted strategic dosing
This is an adjustment to this plan – with a key added feature: FWECs* (faecal worm egg counts). Using FWECs allows us to take into account individual infection in each horse. This means we are covering all bases: time of year, life cycle of the worms, weather, environment (pasture management), individual burden and avoiding drug resistance. This plan will be individual to each property, and it is why there is no simple answer to the question “when do I worm my horse?” Regular FWECs identify horses most susceptible to worms (and who are the biggest contaminators of pasture) so that these can be de-wormed and others (with a FWEC of under, say, 250epg) are left alone – this can reduce anthelmintic use by over 50% and helps us avoid drug resistance. However there is a catch – the FWECs only detect adult worms, therefore a larvicidal product should be used on all grazing horses once yearly (usually in winter). Equally tape worm is not detected in the FWECs routinely so they should be treated with a tape-worm wormer once a year too (when doesn’t matter – they aren’t very seasonal).
*FWECs – these are measured in epg (eggs per gram). We know that some worms will be around on the pasture, and your horse or pony may have one or two floating about inside without any trouble. Each worm has its own egg that we can recognise and we know what burden causes a problem for horses. We will decide what level is acceptable for your horses, but something like 250epg is no problem at all. Aiming for a FWEC of 0 is pretty impractical, and sometimes impossible!