Wormer – are you weight aware?

26 April 2017

Rosie Naylor BVetMed MVetMed DipACVIM MRCVS, RCVS Specialist in Equine Internal Medicine

Wormer should be administered in relation to the weight of your horse. Before worming make sure you know your horse’s weight as accurately as possible and use the correct dose of wormer for the horse’s bodyweight.




Why is accurate dosing so important?

Currently in the UK, there is growing evidence of equine wormer resistance becoming a significant problem. This increase of wormer resistance has been brought about by the widespread and often unnecessary use of wormers, and, probably more importantly, the systematic under-dosing of wormers through poor weight estimation.

Prior to worming, very few horses are accurately weighed on a weighbridge. More often than not, the dose of wormer a horse receives is based on a visual estimation of its weight. Unfortunately, visual interpretation of a horse’s weight is very unreliable. Studies have shown that horse owners and handlers tend to under rather than overestimate their horse’s bodyweight (Asquith et al 1990, Ellis and Hollands 1998). Most people underestimate weight by approximately 20%. This means that many horses may be unintentionally under-dosed with wormer.

Under-dosing exposes worms to a sub-lethal dose of wormer. Worms that survive this low dose can become resistant to the wormer drug. These resistant worms breed and multiply forming large colonies that are resistant to that wormer drug.

Take Direction

All members of the equine community have a responsibility to do everything they can to sustain the efficacy of the currently available drugs by using them responsibly. Take direction on the correct worming approach from your SQP. Remember that your horse’s weight may fluctuate throughout the season, his worming requirements may change from his winter to summer weight!  If you don’t have access to a weighbridge then asks your SQP about the use of a weigh tape. A weigh tape will give you a much more accurate weight assessment than a visual estimation. 

Ask for direction on how to use the weight tape correctly or take a look at the ‘how to’ video on the Virbac 3D Worming website

The correct dose

Once you have established the correct weight of your horsemake sure your horse receives the full dose for his weight. There is more than one way to deliver the full wormer dose. Traditionally owners use a syringe, a sturdy ergonomic syringe is more likely to deliver the correct dose easily. If your horse is difficult to worm then consider wormer in a tablet form. Worming Tabs are easy to use, each tablet worms 100kg bodyweight, and they can be simply added to the feed for stress free worming.