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Wormer Resistance On The Rise
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Wormer Resistance On The Rise

Regular and parasite-specific worming of your horse should be part and parcel of good stable management practice. But just how effective is your worming programme? Recent veterinary research shows that wormer resistance is a growing serious health threat to our horses and vets are concerned that owners are relatively unaware of the implications of the problem.

Increasing parasitic resistance to wormers

Back in 2010 a concerned BVA (British Veterinary Association) launched a campaign to advise owners that in order to slow parasite resistance worming treatments should be based on veterinary diagnosis rather than just routine. Earlier this year however the results of a study by the EVJ (Equine Veterinary Journal) were released which showed that many owners are still blissfully unaware of the issue and in fact of those surveyed, 86% did not realise that resistance was present on their yard.

When surveyed about their parasite control methods, most horse owners admitted being concerned about moving away from the traditional four times yearly worming programme they’ve used for years and adopted the, ‘if it ain’t broken, don’t fix it’ mind set. Vets advise that owners take a worm egg count at intervals during the year and base their worming treatment on veterinary advice following the results of the worm count. Many owners remain unconvinced, fearing that this approach may not be totally effective.

However, the choice of when to worm and what product to use may soon be removed from owners under radical new plans proposed earlier this year by the BVA which would see worming treatments becoming prescription only. A study by the Moredun Research Institute showed that only one of three categories of worming drugs still has a success rate of more than 95% - those containing ivermectin and moxidectin.

Professor Jacqueline Matthews, who helped run the study voiced concerns that new worming products are not coming through and that research has shown a reduction in the length of time existing treatments are effective in controlling worm egg counts; a clear indication that resistance is growing.

Owners in the UK are now being strongly advised to abandon their traditional worming programmes and instead to consult a vet or suitably qualified person for advice in creating an effective worming strategy with the help of faecal worm egg counts. Yards with multiple owners must all worm from the same professionally devised plan and subscribe to having regular egg counts. New arrivals should be worm-counted and treated appropriately before being introduced to groups of existing horses.

Grazing management

Of course, the correct management of turn-out is of paramount importance and it’s vital to remove droppings at least once a week. Not only does ‘poo-picking’ maintain a healthier environment for grazing horses, it also completely disrupts the worms’ life cycle which dramatically reduces the problem of worm infestation. It should also be remembered that stable kept horses are also at risk from worms as eggs can be present in hay and haylage, so they should also be included in the egg count and treatment programme.

If you are in any doubt as to the best worming treatment programme for your horse, always consult your vet for expert advice.

Disclaimer: Of Horse! and sponsors do not endorse nor validate the accuracy of a blog post. Each article is the opinion of the blogger.

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  1. Eve Sherrill York
    Eve Sherrill York
    This is important information. Voted.
    1. autumnap
      Many thanks. x
  2. Skyelav
    In the day we used carbon di sulfide in gel capsules for bots once a year. While other Vets were busy tubing horses, and driving some to madness, or asphixiating a few, my husband was "flipping gas balls" with a balling gun, a trick long forgotten and rarely used. The other de-wormer we used was phenothiazine in a dose syringe. We never had problems. When we switched to self-de-wormers, the trouble began. I personally, never had resistance because I switched around but it was musical drugs in a way, you had to keep records. What a lot of people don't know is you have to also keep the "sand" out of your horses. I had nine boarders and three of my own in FLorida and year around grazing could lead to sand colic and death. Once a week we would fix a hot bran mash in a big tub and for that number of horses we would mix in one gallon of mineral oil. DO that and mix it by hand to see how it cleans. Our horses were all fat, with no back bones showing, and the de-wormers worked better.
    1. southview
      Wow that's all really interesting! I think sometimes we put too many drugs and chemicals into our animals and forget about the natural rhythm of parasite lifecycles and how to exploit it.
  3. AverageJo Equine
    AverageJo Equine
    There is no resistance to a healthy diet and an natural deworming program. Any time you put chemicals in the body (whether human or horse) there will be nasty side effects...even if you don't see them, they are still there.
  4. Mark Calvo
    Mark Calvo
    Thank you for this article My horses are on a six time a year schedule. We change the wormer each time. As for controlling manure, has anyone ever tried putting black oil sunflower seeds in their feeding program? I started using black oil seeds to help with itching. They can also be used to help with weight gain. The maximum amount I have seen being advised is once coffee can full per day. I believe this comes out to four pounds. Don't quote me on that weight but I have a scale in the feed room and found the recommended daily maximum came out to one coffee can. If you decide to use black oil sunflower seeds do some research. I am not a horse care professional and advise you to do some homework before you take my advice. In any case after I started feeding the seeds the neighborhood crows discovered that a lot of the seeds were passing through the horses and not being digested. A pile of horse manure has about a 12 hour life span in my pasture because the crows tear it apart and spread it looking for seeds to eat. I would be interested to hear from others on this.
    1. autumnap
      That's a really good idea. I suppose the crows and other birds would also hoover up any parasites that might be in the droppings too which might naturally help to control the worm burden on the grazing.
    2. AverageJo Equine
      AverageJo Equine
      Flax seed does the same thing. The upside of flax is it is higher in omega 3's so is anti inflammatory where sunflower is higher in 6's so is inflammatory. Though with the flax you see more of the smaller birds rather than crows.

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