Management of Long-Acting Drenches

Long-acting drenches should be used as part of a planned strategy to get the best potential control benefits, while avoiding an increase in resistance by parasites.

Discussing this with an adviser (see link below) is strongly recommended.

• Ensure that the parasite problem justifies the use of a relatively expensive product, rather than a short-acting one. In general, long-acting drenches will have a role only in younger age groups (weaners/yearlings) in years or conditions where pasture contamination is a problem.
• Limit the use of long-acting drenches to the mobs that are likely to benefit most. Some mobs may be at significant risk while others, of the same age and class, may be at lesser risk due to nutritional or environmental factors.
• Check worm egg counts towards the end of the pay-out period for key worms (it varies between species), as positive counts indicate that resistant worms have survived. This triggers the need for a drench to remove these worms (an ‘exit’ drench). Similarly, depending on local drench resistance patterns, a ‘primer’ drench to remove potentially resistant worms prior to treating with the long-acting drench should be considered. These primer and exit treatments should use a short-acting combination product so that worms that survive one active ingredient are likely to be killed by the second or third active ingredient.