Protecting your horse from parasites in the right way is vital, both for his health and to help prevent the problem of wormer resistance. 

There are three different worming programmes you can follow:-

1. Targeted dosing

This method reduces the worming drugs needed and helps prevent resistance to wormers, making it a cheaper option. You will need to have a worm egg count (WEG) performed on your horse's droppings at regular intervals and if there are more than 200 worm eggs per gram (EPG) of faeces your horse will need worming. WECs can be carried out by your vet or you can buy a kit on the internet. A negative WEC does not guarantee a horse is worm free, because he may be harbouring immature worms that haven't produced eggs. Over winter, small redworm larvae hibernate in the horse's gut wall and there is no test at the moment to identify their presence. Tapeworm eggs cannot be reliably identified on WECs either, although a blood test every six months can detect an infestation. Good pasture management is essential to make this method effective.

2. Interval dosing

This method involves worming your horse at regular intervals, based on a product's duration of action. Worming this way removes egg-laying adults and so reduces the number of worm eggs on a pasture. A twice-yearly tapeworm treatment must be included to make the programme effective. The main disadvantage of this method is that the horse may be given a wormer when he doesn't need it, which encourages resistance and wastes money.

3. Strategic dosing

Here, you worm at specific times of the year to disrupt the worm's lifecycle. For example, dose your horse with a de-wormer in spring, the middle of the grazing season and in autumn. The success of the worming programme can be adversely affected by abnormal weather patterns which can lead to early or late peaks in worm larvae or if you miss a treatment for tapeworm or encysted small redworm.

Effective pasture management is the most important weapon again worms. It prevents horses from becoming re-infected by worm eggs in the pasture.

To properly manage a paddock you should:

  • Remove droppings from the pasture at least twice a week.
  • Graze sheep or cattle in your paddocks periodically. They will hoover up any horse worm eggs, which can't survive in other species.
  • Rest the pasture. At least three months rest is needed for significant reduction in the worm burden. Strong sunlight and hard frosts help to kill worm eggs. 
  • Combine harrowing with resting. Harrowing dirty pasture will contaminate the whole paddock but if the paddock is then properly rested the exposed worms will be killed off quicker by sunlight or frost.
  • Make sure there is enough grazing. You should have one and a half acres per horse.
  • Rotate pasture. Divide paddocks up so they can be alternately grazed and rested.
  • Quarantine new arrivals and have their worm burden tested or treated.

Your 12-month plan

When you do need to treat with a wormer it is vital you give the correct dose. Under-dosing means the wormer won't be effective and resistance is more likely to develop. Use a weigh-tape or hire a weigh-bridge for a more accurate reading. 

The active ingredient will be printed on the packaging of the wormer but your vet or an SQP (suitably qualified person) at a tack shop can advise on the correct product for your horse.

January - In the winter, treat for encysted small redworms. WECs do not detect these larvae so all horses will need treating. Moxidectin is proven to be effective against small redworm larvae as is fenbendazole (a five-day course), although it is worth noting that some small redworm are resistant to this drug. Both products will treat other worms and bots but not tapeworm.

Spring and Autumn - In April/May and September/October treat for tapeworm. The active ingredients which treat tapeworm are: praziquantel, which only treats tapeworm or a double-dose of pyrantel embonate which treats tapeworm and other worms.

Grazing season - From April to October carry out a WEC every three months. If your horse needs treatment, use either fenbendazole, a single dose of pyrantel embonate or ivermectin. It is best to rotate wormers when you need to use them, in case you have a parasite which are resistant to one drug.