Wormer Under Dosing – The Often Ignored Risk to Your Horse’s Health
Callum Blair BVMS MRCVS
Some form of worm control programme is essential to ensure the health of your horse. The objectives of a good worming programme are two-fold. Firstly to prevent worm related problems and secondly to minimise pasture contamination with worm eggs from the horse’s droppings.
A good starting point for developing an effective worm control programme is to get professional advice. The law concerning the supply of equine wormers has changed and they are all now Prescription Only Medicines (POM-VPS). In order to have the right to prescribe and supply horse wormers, your local CWG Suitably Qualified Person (SQP) has to undergo an extensive examination process and are required by law to maintain a programme of further training to ensure that they are up to date with current knowledge on the subject.
Even the best designed programme, however, can fail if the recommended dose of any drug is not respected. Very few horses are accurately weighed on a weighbridge and more often than not, the dose of wormer a horse receives is based on a visual estimation of its weight. Unfortunately, this is notoriously inaccurate, with guesses being on average 20% below the actual weigh-bridge weights*. Even less reliable is the guesstimate that a horse weighs the same as “one syringe of wormer will treat”. Weigh tapes provide an easy way to get a more accurate indication of your horse’s weight, ensuring you know how much wormer you should administer.
A less obvious source of under dosing is “spit-out” but most horse owners have experienced this problem at some time. In a recent survey only 25% of horse owners described worming their horse with a syringe as very easy and only 30 % claimed to be successful in administering the full dose every time.
The true significance of spit-out becomes apparent when you realise how much (or little) paste/gel is in a syringe. For most products this is between 7 and 10 ml or put another way, about a rounded teaspoonful. Consequently, that dribble on the floor after worming could account for as much as 50 to 80% of the dose administered.
Under dosing reduces drug efficacy resulting in poor worm control and potentially serious health problems for your horse. It also significantly increases the risk of drug resistance which is something we should all be concerned about.
Don’t be tempted to under dose your horse and if you do experience any problems or have any concerns, speak to your CWG SQP for advice on all aspects of effective worm control as well as alternatives to syringes.
*Asquith et al. 1990, Ellis and Hollands 1998.