Deworming Considerations When Moving Horses

The easiest way to acquire a resistance problem on your property is to import it with new horses.  Horses that arrive on a new property can carry resistant worms that can then be deposited onto the new property and contaminate the pasture with resistant worm eggs. 

A good quarantine procedure can minimise the risk, but a poor one can potentially make things worse.  By putting some simple steps in place, you can reduce the likelihood of unknowingly introducing a resistance problem on your property.

Firstly, you need to make sure that any new horses coming onto your property can be isolated from all resident horses. This is best managed by using a holding yard, stable or small paddock where you can keep the new arrival by themselves. The less grass in the yard, the better!

Next, administer effective deworming products to ensure that all adult and larval stages within the horse’s intestine are killed. This is likely to involve using a combination of two different deworming products (see table below). The use of a single active anthelmintic treatment as a sole quarantine measure is not recommended as it ensures that the only worms brought onto a property are those that are resistant to that treatment. Collect and dispose of manure daily.

After five days, move your new arrival to a paddock that has previously been grazed by other horses on the property. The new horse should still be isolated from resident horses, though can share the paddock with cattle or sheep.

Fourteen days after arrival, collect a manure sample from each new horse and send away for a Faecal Egg Count. This will check the effectiveness of the deworming products that you administered at the start of the quarantine program. The results should show an egg count of zero.

Your new horse can now be safely introduced to the rest of the horse population on the property and added to your regular deworming testing and treatment program.

Young horses under the age of two are frequently moved between properties (for education and training, for example) or to new owners. This age group is at risk of ascarid (roundworm) infection, as they primarily only affect horses under two years of age. Once horses mature, they develop a natural immunity to ascarids and so these worms are rarely seen in older horses. As ascarids are such a large worm that can quickly develop into life threatening numbers and are the most significant parasite in horses under two years of age.

Also be cautious when acquiring any horse with an unknown worming history, or one that has gone an extended period without being wormed. Horses in this situation need to be given special consideration prior to deworming in case they are carrying a large burden of worms.

For either of these situations, it is a good idea to perform a Faecal Egg Count when the horse first arrives on the property. Keep the horse isolated in a small yard until you have received the results and then drench accordingly. The drench day then becomes day 0 and you can continue to follow the instructions in the table below.