Tailored horse worming programmes ensure specific worms are targeted with an effective product at the right time.
There are four main classes of anthelmintics (horse wormers):
1.Benzimidazoles: e.g. fenbendazole/mebendazole
2.Tetrahydropyrimidines: e.g. pyrantel embonate
3.Macrocyclic lactones: e.g. Ivermectins/avermectins
4.Praziquantel based wormers (tapeworm treatment ONLY)
Using the same class of horse wormer every season will increase the chance of resistance developing. It is therefore important to rotate the class of wormer used after each grazing season.
Worming throughout the year
In February and November it is important that horses are treated for encysted small redworm. This is to prevent mass emergence in the Spring. There are two types of wormer that can be used for this, fenbendazole or moxidectin based wormers.
Horses only need treating for tapeworm twice a year as the lifecycle takes six months to complete. This should be done in March and September. This can be done using a praziquantel or a pyrantel based wormer.
Horses should be treated for bots after the first frost of the winter with an ivermectin or moxidectin based product.
During the grazing season (April to October) faecal worm egg counts should be performed regularly to determine whether horses need worming and if so with which wormer. Your vet will be able to advise you on this.
It is, however, important to remember that faecal egg counts cannot detect encysted small redworms or tapeworm eggs, so it is important to treat for these parasites at certain time points during the year as previously described.
An alternative product should be used for each subsequent year’s grazing season so that the three main types/classes of anthelmintic (praziquantel is excluded from this rotation as it only treats tapeworms) are used on a rolling three-year basis, as shown in the picture below.
Worming a New Horse
If you have a new horse, it is sensible to worm them with a product or combination of products that will kill all types and stages of roundworm (including encysted and inhibited small redworm) and tapeworm. Stable your horse for 48 hours after worming to allow the wormer to take effect and prevent viable eggs from being deposited on the pasture.