Vet Essentials: When it comes to worming, are you underdosing?

In this new companion article to our Vet Essentials series, we take a look at this issue of weight in relation to worming and ask if you are actually underdosing.

Are you weighing before worming?

Are you guilty of guessing your horse’s weight rather than weighing before worming? If so you could be in danger of underdosing.

Underdosing can cause worms to develop resistance to the wormers used and this can have a serious impact on how we may manage worm burdens in the future.

The British Riding Clubs Horse Health survey commissioned by Zoetis last year revealed that 44% of the horse owners asked do not weigh their horse before worming.

Case studies

The issue of weight was recently highlighted in some case studies from a private yard in Suffolk. Cindy is a 13.1hh Connemara mare in ‘summer’ condition. Her owner was very surprised when the weighbridge clocked her up to 380kg – a full 60kg more than was expected.

Usually Cindy’s owner splits one wormer designed for dosing a horse up to 600kg in weight between two similarly sized ponies which means she has been significantly underdosing.

Pop is a 16.1hh Irish Sport Horse gelding. His owner admitted that he is carrying a few surplus pounds but was shocked when he tipped the scales at 638kg. She had recently wormed him for a weight of 600kg – the maximum weight of the worming syringe she had bought.

Dec is a 16.3hh Warmblood. He is lean lithe and competition fit but still weighs in at 674kg.

“Our case studies give a very real perspective on how easy it is to underestimate the weight of our horses” says Wendy Talbot Zoetis vet.

“Ideally you should weigh your horse at least once a year using the accuracy of a weighbridge – several feed manufacturers offer a portable weighbridge service. Weigh tapes although less accurate are a great way to keep tabs on weight once you have the accuracy of the weighbridge weight to refer to and have factored in any discrepancies. Remember that many horses will change in weight throughout the year.”

Resistance

Resistance to wormers is a growing problem. When a parasite population previously controlled by a drug is no longer susceptible to that drug it is known as resistance. The active ingredient of the horse wormer kills the sensitive parasites in the population but those parasites not affected go on to create new generations of resistant parasites. Eventually if the process continues only resistant worms remain in the population. Frequent dosing or underdosing can cause resistance to occur reducing the effectiveness of the wormer.

Knowing the current weight of the horses that you wish to treat before purchasing your wormers can help your vet or SQP to ensure that you buy the correct dose in each case.

Visit www.esrw.co.uk to test your knowledge of encysted small redworm and speak to your vet or SQP about responsible worm control. To find out more about year-round worm control visit www.wormingyourhorse.info. You can also download Stable Mate the horse health management App from Zoetis. It is available from the iPhone App Store and Google Play Store: text Stable Mate to 80800 to download.