Horses with worms will shed eggs onto the pasture, as a part of the parasite's natural life cycle. However, some horses will naturally cope better and shed less worm eggs.
On the other hand, some horses, especially debilitated or young animals, will pass more worm eggs in their faeces. These 'high shedders' can infect the pasture in a short space of time and consequently increase the pasture challenge to other horses that share their grazing. For this reason it's important to identify these risk animals and treat them appropriately.
Young animals are more prone to infestation and are usually the main source of egg shedding. It is best to keep a close eye on your young stock and manage the group accordingly.
The environment of mares and foals should be as well managed as possible.
Where necessary, mares should be wormed just prior to foaling, while foals can be wormed from four to six weeks of age with an appropriate wormer.
nUse faecal worm egg counts. Use faecal worm egg counts (FWEC) properly (see worm testing panel, far right).
Remember a single FWEC is only a rough indication of your horse's worm burden at a specific point in time and results may vary between consecutive tests.
FWECs are very useful for identifying which horses are shedding high numbers of eggs.
Regular FWECs throughout the grazing season will in time build a clearer picture of your horse's worm burdens and shedding patterns. It's the best way to identify which horses need routine treatments and those which do not need worming every time. Costs vary for FWEC tests, but are generally €10-12 per sample.
nDose accurately. When you have identified that a wormer is needed, you should always select the one most appropriate for the parasite you are targeting. You must also make sure you treat your horse accurately according to weight. This will help to maintain the effectiveness of the wormers available.
nClean pastures. Clean grazing reduces overall worm burdens and reduces the need for excessive use of wormers. Pick up droppings regularly during the grazing season – ideally every day. If this isn't viable, consider smaller paddock sizes so that each field can be alternately grazed, harrowed and rested.
Cross-grazing with sheep and cattle is also effective at reducing horse parasite burdens on the pasture as they will 'hoover up' the worms without being affected.
nChoose your wormer carefully. Take advantage of the persistent effect of some wormers.
Some wormers, such as those containing moxidectin, have persistency against cyathostomin larvae.
For high risk horses, using these products at the beginning of the grazing season may well mean that your horse could provide a 'clean up' mechanism for the pasture for the first couple of weeks.
This may reduce the overall worm burden on the pasture and in your horses, reducing the build up of worms over the grazing season and hence reducing the number of worming doses needed over the later summer months.
Consult with your vet as to whether a wormer is required at this time for your individual horse.
nDose strategically. Remember to strategically dose for tapeworm in the spring and autumn and for encysted small redworm and bots during the winter. FWEC tests won't detect these latter parasites, but your worming regime, if carried out correctly, should control them.