|  To worming products What exactly is resistance? Resistance is when a greater frequency of individuals in a parasite population, usually affected by a dose or concentration of compound, are no longer affected. Once resistance is present in a worm population, the health, welfare and performance of horses infested with resistant worms will be compromised. For this reason it is essential that your horse is dosed accurately according to bodyweight. Using too low a dose of wormer may speed up the development of resistance. On the other hand, frequent, unnecessary worming may also increase the potential for development of resistance. The key to reducing the likelihood of resistance is choosing the right wormer, then giving it at the correct dose and time. Worm egg counts have an important role in this, as they help you to identify when your horse actually needs to be wormed. Use worm egg counts as part of a SMART worming programme. Resistance - • Benzimadazole (BZ) resistance recognised in Kentucky in 1965 and first reported in UK in 1974
- • Surveys have shown that where BZ resistance has been confirmed, continued use of this chemical group of wormers resulted in an increased level of resistance
- • Even after a prolonged break from this group of wormers, worms remain resistant and this cannot be reversed
- • Resistant strains are easily spread by horses grazing together and this is more likely in groups of more than 6 horses
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