Dealing with Worms in Horses: Manage, Test, Plan, Dose

If you’re a horse owner, there is no doubt that you have at some point had to deal with the menace that are worms. Dealing with worms in horses doesn’t have to be difficult and that is where Pfizer comes in. In time for the 2012 worming season, they released a new website detailing a four point plan that allows horse owners to effectively combat worms in horses.

The plan incorporates four key actions and they are; manage, test, plan, dose. Unfortunately, dealing with worms in horses isn’t as simple as giving your horse a dose of wormer and hoping for the best, which is why Pfizer put together the four point action plan. Below we’ve taken a look at each point and how they can help you to deal with the worm menace.

Managing Your Horse to Reduce the Worm Threat

An effective worming plan begins with how you manage your horse on the pasture. The small pastures we let our horses roam on allows a high density of worm eggs to build up, by correctly managing the pasture, we can reduce the impact this has on reinfecting our horses.

The cycle of infection begins when an infected horse excretes worm eggs in the faeces, on to the pasture. The eggs develop in to larvae outside of the horse and lie in wait within the grass. A horse that eats contaminated grass ingests the larvae allowing them to develop within. Eventually, the larvae develop in to adults, lay eggs which are excreted in the faeces and the cycle continues.

To reduce the level of reinfection, these steps can be taken at a management level:

  • Clean the pasture from faeces as often as possible (at least every two weeks)
  • Graze the pasture with cattle or sheep as worms are host-specific (i.e. worms in horses will not generally infect sheep or cattle)
  • Rotate pastures to allow them to ‘rest’, bad weather can cause some larvae to die reducing the worm burden
  • Don’t overstock pastures with too many horses as this will speed up the cycle of infection

Testing for Worms in Horses to Know When to Treat

You should test your horse for worms using a faecel worm egg count (FWEC) and a tapeworm antibody test (TAT). Tapeworms cannot be detected with a standard FWEC, nor can they be treated with the same dewormer.

A quick Google search will reveal sites near you that offer testing services, such as Myerscough College, UK. Sites like these offer a cheap, yet essential service. By sending a sample of faeces, they can determine the worm burden and give the result in eggs per gram. A result that is above 200 eggs per gram of faeces is consider high and should be treated.

You should conduct a FWEC and TAT at least once a year, an ideal time to test would be spring or summer.

You can use the results in a number of ways – you can see if your worming treatment is working (by testing before and after), you can see whether or not you need to worm (if the result is low <50 eggs per gram), or you can see if a worming treatment is urgently needed (>200 eggs per gram).

Note that Bots, Pinworm and the immature larvae of Redworm or Roundworm cannot be detected by either a FWEC or TAT.

Planning an Effective Worming Procedure

Worms in horses can be a problem all year round, whilst Tapeworms might only be a problem during Autumn or Spring. As such, you should take note of all your FWEC and TAT test results to see when worms are going to be the biggest problem for you and your horse.

There are a number of factors that can determine when in particular worms might be a problem, these include:

  • Age – Younger horses can be more susceptible to worms, although not all dewormers are suitable for young foals
  • Health – Ill or immune compromised horses can be more susceptible to infection and may also be more likely to shed worm eggs in their faeces. Stress can also play a large factor in how a horse deals with worms
  • New Horse – When bringing a new horse to your pasture, you can’t be sure of their previous worming status and whether they are a risk to any horses you may already own. As such, be sure to get them tested and treat accordingly when the results are returned
  • Pregnancy – Pregnant mares, like ill horses, are more susceptible to worms. You should plan accordingly by providing pregnant mares with dewormers considered safe for use during pregnancy. This is important as the larvae of some worms can be transferred to a new born foal via its mother’s milk

Delivering an Effective Dose to Treat Your Horse

There are four scenarios where Pfizer recommends treating your horse:

  • If your FWEC returns a result over 200 eggs per gram
  • Your TAT is positive and/or you have not treated for tapeworm in the past 6 months
  • It is late autumn or winter and you need to treat for encysted small redworm
  • You have a new horse which needs a quarantine dose

When giving treatment there are two crucial things to remember:

  1. Do not underdose – underdosing can lead to resistance (use a weigh-tape to measure your horse’s weight and follow the manufacturer’s guidelines on dosing for that weight)
  2. Do not deworm too frequently – this too can lead to resistance, combine you deworming treatment with good planning (i.e. using FWEC and TAT tests)

For more information on the four point management program – see here.

About James Watts

BSc Bioveterinary Science. Editor of PetSci. When I'm not writing, learning, discussing, or reading about animals, you know it's the weekend! Currently developing PetSci HealthTrak, the fast and easy way to monitor your pet's weight and calorie intake. HealthTrak offers a simple way to track your pet's progress, helping them achieve a healthy weight and a long, happy life.

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