Everyone will admit that horses MUST be wormed regularly over the warmer months, but there is an increasing problem of resistance to horse wormers - a study in the UK and Europe found worm resistance on 82% of yards to the wormer active ingredient ‘Fenbendazole’, which is in many brands of wormer.
Therefore to preserve the current wormers we advise a more targeted approach to worming horses. The aim of targeting is to only worm your horse when they require worming. We do this by taking worm egg counts from a sample of your horse’s dung. There is a cost for this but in the long term for horses that only require 1-2 worming treatments a year the overall cost is actually less. Be careful to check how the sample is being examined, some techniques are better suited to horse samples than others, we find the more suitable and complete examinations cost more but are well worth it for peace of mind and confidence in the result.
Taking dung samples is as simple as picking up 1-2 balls of fresh dung from your horse, place in a small plastic bag e.g. a freezer bag; labelling them with your name, address, your horses name; the date you last wormed your horse and the wormer product you used at that worming. Then drop the sample them off at the sugery for analysis. If the sample is sent off to an external laboratory results are normally back within 3 working days. Unfortunately worm egg counts are not reliable for assessing if your horse has tapeworms. To check for tapeworms your vet needs to take a blood sample and send it off, the laboratory looks for antibodies to the tapeworm and indicate the level of infection intensity in your horse. This can be done at any time of year and so we often do it when we are giving your horse its annual health check and vaccination.
As well as a targeted worming program other methods are equally as important in reducing the worm population:-
Poo picking paddocks at least twice weekly in summer and once weekly in winter
Grazing sheep with horses or following the removal of horses
Avoiding grazing foals and young stock on previously grazed pasture every year
Our current best practice advice is to start taking dung samples from your horse in the Spring (normally April but if the spring is cold and wet you can wait until May when it warms up.) If the egg count is less then 100 eggs per gram, you should take another dung sample 12 weeks later. If the egg count is between 100 and 200 eggs per gram you should take another dung sample in 6 weeks time. If the egg count is greater than 200 you should worm your horse (your vet will advise which worming product based on what you have been using previously and the time of year), and then take another sample 2 weeks later. The reason for this is so we can check your horses’ worms are not resistant to the wormer you have used. If there is no resistance then the count will be zero or very low.
In a lot of cases we do not need to use any routine wormers in our patients based on the results of samples, but you must always discuss the results and the appropriate management with one of our vets, even if the result is low or zero. They will want to ensure that tapeworms and cyathastomes in particular, are controlled as these two parasites can cause severe colic.
Whatever method of worm control you are using it is always advisable to check how effective your control is by taking a dung sample during the summer.
It is worth bearing in mind that some products are not suitable for use in young foals and so your Parkside vet’s advice should be heeded as to the best product to use in young foals. Horses do develop natural immunity to worms as they get older.Tthis immunity protects adult horses from developing a large worm burden if there are able to graze clean pasture. Young stock up to 3 years old will not have developed their immunity fully, so need more frequent attention (dung samples) and possibly worming treatments and as horses get older their natural immunity can start to reduce so they also need to be monitored more carefully and frequently.
Any new arrivals to your yard should be wormed with a broad spectrum wormer and then a dung sample taken 2 weeks later (while they are still in isolation) to check they have not brought a resistant worm onto your yard. We advise a minimum 3 week isolation period; this allows for you to get a dung sample tested and have the results back before the end of the isolation period. This length of isolation period also protects against the new horses bringing other infectious diseases such as strangles and ringworm onto your yard.
In summary with no new worming products likely to become available for the foreseeable future we need to use wormers only as required to try to slow the build-up of resistance, targeting the use of a wormer with the horses that need them by using dung and blood samples. This will save you money, reduce your reliance on wormers and slow wormer resistance development.
Article by Dr Alistair Crozier for the Scottish Equestrian magazine