Replacing the much-used 28-day drench routine with smarter choices on when and how often lambs get drenched could help reduce resistance development and improve livestock productivity.

Dr Abigail Chase, veterinary parasitologist for Boehringer Ingelheim Animal Health New Zealand, believes on the whole Kiwi farmers have picked up well on messages on drenching practice that came from research done in the 1980s.

“The research is that preventing larval build-up on pasture will always result in more effective worm control – rather than waiting for levels to actually rise and then trying to deal with them.”
As a result most NZ farmers have adopted regular four-weekly drench programmes, but her concern is this is almost too much so.

“What we tend to see now is we’re going in early to control worm levels, especially when we use capsules in ewes, but not reaping the rewards of a pasture with low larval challenge by drenching less often.

“There may be a need there to just think a bit harder and smarter about whether drenching this time around is really such a good idea.”

The result of more drenching is greater exposure to drench actives by parasites than may be necessary and almost complete elimination of any refugia parasite populations within the livestock being treated.

“Maintaining these refugia (undrenched) parasites becomes vital as drench resistance grows as an issue in some areas. Good management can help push out that risk.”

Seeking vet advice, and using Faecal Egg Counts results can often cost significantly less than a round of drenching, and pay off for many seasons afterwards, says Abigail.

“It may be a case of doing a FEC check before launching into a weaning drench, and getting more strategic about it.”

Farmers not comfortable with not drenching at all could get selective on which animals they drench.

“It could be you elect to draft off the lighter half of a lamb mob and only treat them, and possibly decide to up their feed levels.

“You just have to be quite clear about how you want to go about pushing that resistance risk out, and what the simplest management options are in front of you.”
Another option to help reduce parasite loadings is working on how parasites are controlled in older stock, such as ewes.

“Older stock may be left out of the drench equation, when in reality their worm loadings can have a compounding effect upon young stocks’ loadings.”

Using a long-acting capsule treatment in ewes can contribute directly to improving lactation levels, in turn boosting lamb growth rates and improving their immunity levels to parasites.

“If you reduce exposure to lambs you shouldn’t have to drench as often. Less larvae on pasture means less disease for the lamb, but also less refugia – another reason not to reduce refugia more with possibly an unnecessary drench.”