By Vet Emma Trott
Did you know that 20 per cent of horses carry 80 per cent of the worm burden?
Instead of routinely worming our horses, we should be monitoring to determine if a wormer is necessary. Overuse of wormers leads to resistance which then means that our wormers will not work in future. For adult horses we are particularly concerned about small redworms, encysted redworms and tapeworms. A high worm burden can cause weight loss, poor condition, diarrhoea and colic.
Worm Egg Counts
Worm egg counts, which look for small roundworms, have become an important part of any horse’s worming programme.
We advise that horses have a worm egg count every three months throughout the grazing season. Worm egg counts are less useful in the winter as the small roundworms can go into a dormant state and not produce eggs. Worm egg counts do not detect tapeworm therefore they should be used as one part of the worming programme.
How do you get a worm egg count? We require a small amount of fresh poo to be collected into a bag and delivered in to your vet practice or posted to a suitable lab. It is best if you take a small sample from three different areas of poo to get the most accurate result.
This poo sample will be looked at under a microscope to determine how many eggs per gram (epg) were present. A horse with over 250 epg is likely to be advised worming.
Tapeworm
Anoplocephala perfoliata, also known as tapeworm, is a common parasite in horses. Previously, we have always wormed horses twice a year for tapeworm. However recent studies have shown that only 23% of horses need worming. Therefore, we recommend that horses have a simple saliva test to determine whether they require treatment. This test looks at whether the horse has antibodies to tapeworm; these antibodies remain after the horse has been wormed, therefore it should not be used if the horse has had a wormer for tapeworm in the last six months.
Encysted Redworm
During the winter months small redworm encysts in your horse's intestines. These lie dormant, and then can mass emerge as the weather warms up which can cause serious illness. Traditionally, we would worm horses in the winter to cover for this.
As discussed above, worm egg counts are less reliable in the winter therefore we need other methods to determine if the horse requires treatment. Typically, a winter wormer is given to cover encysted redworm and tapeworm. However, instead of this we can now use a combination of a blood sample for encysted redworm and a tapeworm saliva test to determine if this is necessary. Please speak to your vet to determine if these are suitable for your horse.
Here are our top tips for managing your fields to help reduce your horse's worm burden. In turn this can help to reduce our reliance on wormers, reduce resistance and therefore keep our horses healthy for longer!
Our tips are: Use appropriate worming techniques, do not routinely worm horses, use worm egg counts regularly and ensure all horses are tested.
Field companions will often have a different worm egg count from each other; therefore we can’t assume that one horse having a low or high burden will reflect the herd.
Also important are: Regular poo picking, keep horses within the same grazing groups, do not spread muck on fields, clear all muck from fields before harrowing and reduce stocking density (have less horses per acre). Also co-graze with other species such as sheep and rest fields appropriately.