New Zealand farm systems shift towards condition-based pre-lamb drenching to combat worm resistance

Veterinary experts and industry guidelines are encouraging farmers to reduce its reliance on routine drenching by focusing on sheep condition and integrated parasite management, aiming to slow resistance and improve ewe health post-lambing.

Veterinary advice on pre-lamb drenching is changing as farm systems adjust to put sheep condition ahead of parasite routine. VetSouth says more farmers are reducing drench use in adult stock, particularly around lambing, after improving feeding and body condition so ewes can better withstand worm pressure.

Where ewes are light or feed is short, a drench may still be justified. Short-acting oral products will clear parasites carried through autumn, while long-acting bolus or injectable options also suppress incoming larvae for longer, depending on the product. But VetSouth stresses that treatment only works if the drench is effective against the worms present on each farm, and it recommends veterinary advice before selecting a product.

The wider industry message is the same. New South Wales government guidance and other veterinary resources say worm control should combine drenching with grazing management, nutrition and breeding for resistance, while preserving refugia to slow drench resistance. Over-use can undermine both immunity and efficacy.

VetSouth also advises caution with long-acting products: ewes should ideally lamb on paddocks that will later be cropped, or be mixed with undrenched stock. A faecal egg count 60 to 80 days after dosing is needed to judge whether the treatment has worked and whether it remains a viable option.