It is widely accepted that in order to reduce the risk of build up in resistance to a particular drug group, a rotation should be adopted between the three major drug groups. Many horse owners don’t find this as easy to follow as you would think as the drug groups aren’t always evident in the name of the wormer you may be using.
The three major groups are:
| Macrocylic Lactones | These include Ivermectin and Moxidectin |
| Tetrahydropirimidines | Such as Pyrantel Embonate |
| Benzimidazoles | Including Fenbendazole, Mebendazole & Oxibenazole. |
To complicate matters further, different wormers (even in the same group) can treat different types of worms. They can also have differing periods of effectiveness for your horse.
How - I often hear, are you supposed to know what to use and when?
Firstly, you should take the advice of a Suitably Qualified Person (SQP), such as us at Wormerclub, regarding when to worm & what to use. We will always explain the reason for selecting the wormer we prescribe and in doing so try and give you as full an understanding as we can about the drug group, length of effect and so on.
A common mis-understanding about wormers is that they stay in a horses system for a period of say 6 – 12 weeks and therefore provide protection against a worm infection for this period. However in most cases (not all), the wormer has an ‘instant and one off’ effect. This kills the worms, larvae and eggs in a horses system on the day it is used and for a very short period afterwards. Therefore within days after worming a horse can easily pick up worms, eggs and larvae when grazing. There is however a period of time before these larvae or eggs develop to a stage where they can be a 'worm burden' on your horse. Around this point your horse will need worming again. This period is therefore considered the effective period of the wormer.
Most of the manufacturers of horse wormers recommend an annual programme to follow. We have provided copies of these programmes on our ‘worming calendar’ page. We have also attempted to offer some optional annual programmes that utilise a combination of manufacturers products and may often work out cheaper over the course of a year. If you are in any doubt, please contact us on enquiries@wormerclub.co.uk and we will be delighted to help.
