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Base Chemicals in Wormers
………………so you want to know about the chemicals in horse wormers.
Some of the wormers that have different brand names contain the same chemical and therefore are chemically identical. This information sheet groups the wormers by their main chemical ingredient to help you choose the wormer that you need.
All of the wormers available in the UK are from four chemical groups. It is important to rotate the chemical group on an annual basis. If you do not do this and worm with for example Equest every year then eventually worms will become resistant to the chemical moxidectin. This has already happened with the chemical benzimidazole and in certain horses the Panacur and Telmin wormers are ineffective against adult worms.
It is important to change the chemical group on an annual basis but you MUST NOT switch between chemicals each time you worm. This will increase the speed at which worms become resistant to the chemicals. There are only three chemical groups to rotate between as Group 4 praziquantel only treats tapeworm.
Fenbendazole & Menbendazole
EFFECTIVE PERIOD OF COVERAGE
8 - 10 weeks
6 - 8 weeks
4 - 6 weeks
tapeworm 6 mths
tapeworm 6 mths
Each chemical is effective against different types of worms and some treat both adult and larvicidal stages. The table below provides a quick and easy to read comparison