Get to grips with some of the common terms used to explain worms and worm control with our HorseDialog jargon buster
25 September 2020Read More
Do you weigh a horse before worming? The answer is yes. A report from the British Riding Club has found that 44% of horse owners don’t weigh their horses before worming. Why does this matter? – because there are serious consequences to both overdosing and underdosing.
Most wormers come in syringes for oral administration or packs of powder/granules for adding to food. They are clearly marked with dosing instructions based on the weight of the horse and should be followed carefully to avoid overdosing.
If you are concerned that you have given more than the prescribed dose, or you horse seems off-colour after worming you should speak to your vet immediately. Ensure you have the details of the wormer to hand and how much you think your horse has had.
In particular, some individuals such as foals, animals with underlying health conditions or the elderly may be more susceptible to the effects of overdosing. Also bear in mind that the relative effect of a small overdose in low body weight animals such as miniature breeds is higher, which means they too may be more susceptible. Rarely, just as is the case with any medication, an individual animal may show an allergic reaction to a particular wormer.
Giving too little wormer can actually be a far more serious problem than giving too much. Wormers contain an active ingredient designed to kill the parasites and this ingredient needs to be at the right concentration in the body. When the dosage is too low, some of the worms can survive, especially if they have a degree of resistance to that wormer already – they may well have been killed if the wormer was at the right concentration but the lower dose allows them to survive. The survivors can then reproduce and pass on their resistance to further generations of worms. Over time, a resistance to that wormer builds up in the worm population so that even when used at the right concentration many worms survive the wormer, making it ineffective. It’s important to understand that when you underdose, the consequences don’t just affect your horse – you’re helping to breed a new population of wormer-resistant parasites and making existing treatments less effective for all horses.
Getting the correct dose
How to weigh a horse
The most accurate way to assess your horse’s weight is by using an equine-specific weighbridge, but most horse owners don’t have one – no surprise when you consider they cost thousands of pounds. Some people have access to a public weighbridge: you drive your lorry with the horse inside onto the weighbridge, record the weight, then remove the horse (in a safe place) and record the weight of the empty lorry. You can then calculate the weight of the horse by subtracting the weight of the empty lorry from the weight of the full lorry. Alternatively, some feed manufacturers provide weigh sessions at yards or your veterinary clinic may have a weighbridge that you can access.
If using a weighbridge is not an option, the next most accurate method is to use a weight formula based on heart girth and body length measurements. Instructions on how to perform this correctly can be found at: AHT
An alternative and more convenient option, but slightly less accurate is to use a weigh tape. You can get one for less than £10.
Whichever method you use be consistent and always weigh a horse before each worming. You’ll get a more accurate idea of your horse’s weight fluctuations if you use it at roughly the same time of day and in roughly the same circumstances. If you do get a chance to use a weighbridge, take the opportunity, so that you can reassure yourself about the accuracy of your weigh tape and measuring technique.
Other related content:
Be prepared to clear the challenge of encysted small redworms and “Time it Right” this autumn/winter.