Successfully Worming Horses

Successful worming of horses can be tricky. Unfortunately worming will never clear all of the worms from a horse.

A novel approach to worming horses has been developed by CSIRO so we thought we’d share it with you.

Why is successfully worming horses so tricky?

Worming involves placing a chemical into the gut that kills adult worms.  But here’s the catch - worm larvae (the immature stages of worms) leave the gut and move all around the body.

Worm larvae can go into an inactive stage where they live outside the gut where they hibernate before moving back into the gut. It has been estimated that at any one time, 90% of worms in a horse are not actually even in the gut!

When adult worms in the gut lay eggs, eggs pass out with the faeces and contaminate the pasture. These eggs hatch into larvae on the ground and when the horse is grazing, these eggs and larvae then get eaten  e-enter the horse’s body and the worm life cycle continues as shown below:

Eggs » Larvae » Adult Worms » Eggs » Larvae » Adult Worms » Eggs » Larvae » Adult Worms

There are lots of effective worming products available on the market that can kill adult worms and keep horses fit and healthy. In combination with regularly picking up and removal of horse manure from the paddock (every single day is best), strategic worming can be a very effective way of making sure a horse is in the best possible health.

A general recommendation is to make sure that all horses receive a worming treatment for gut worms, tapeworms and bot fly larvae in late autumn/early spring.

Key Fact 1: No one chemical kills all of the different types of worms or stages of worms that horses are infected with.

Key Fact 2: Horse worms become resistant to chemicals and as this resistance develops, gut worming chemicals become less effective.

In a world first, CSIRO has been researching and developing a fungus that works in a slightly different way to traditional horse worming chemicals. It is given to horses as a food additive and the fungus passes through the horse without being digested. The fungus then starts to work on the faeces when it’s on the ground. It does this by building a web in the faeces that traps worm eggs and worm larvae. This puts a handbrake on the worm lifecycle because the horse is no longer eating the eggs and larvae off the pasture, the worm lifecycle is interrupted and the number of worms inside the horse will be reduced.

Key Fact 3: This fungus targets eggs and larvae in a mechanical way so unlike worming chemicals, worms cannot become resistant to the fungus.

Can we monitor how our worming and pasture management programs are working?

Yes we can! A very effective way to do this is to have faecal samples examined under a microscope for worm eggs to detect numbers and type of worms present in the animal. This test is cheap to do it’s called a faecal egg count. Have a chat to your vet about getting faecal egg counts done. It can be a very cost effective way of monitoring the success of your existing program and whether any changes can be made. Possible changes after doing a faecal egg count might be – reducing the number of worming treatments, changing the type of wormer being used or increasing the frequency of worming treatments.

We hope you find this information useful to guide your worming and pasture management programs.