Farmers buying in stock this autumn are being reminded of the importance of quarantine drenching to prevent importing drench-resistant worms onto their property.
Beef + Lamb New Zealand’s Wormwise programme manager, Ginny Dodunski, said bought-in lambs and calves pose the biggest risk when it comes to importing drench-resistant worms, but replacement ewes, if they have an unknown drench-resistance status, should also undergo a quarantine protocol.
For sheep, the gold standard quarantine drench is a combination of Zolvix or Startect and a Benzimidazole (BZ) /Levamisole drench (given separately but at the same time).
For calves or R1 cattle, Zolvix is the only novel drench registered for cattle and should be given at the same time as BZ/levamisole combination. The Wormwise website details “compromise” options to these “gold standards” and also outlines what drenches are not suitable for quarantine.
Dodunski said the quarantine drench protocol is just as important as the product used.
It is important to remember that drenches kill only adult worms and larvae; they do not kill eggs.
This means eggs will continue to pass out of new stock until all the worms laying them are dead. This can take up to three days.
After drenching, stock ideally should be held in a bare yard or on grating, with feed and water, for 24-48 hours. Eggs that pass out of the animal and hatch into larvae have no moisture or blades of grass to live on, so they die.
Dodunski said the alternative is for newly arrived stock to be run into a specific quarantine paddock for 24-48 hours. This paddock cannot then be grazed by the same stock class for several months.
For example, adult cattle should be the only stock to graze a lamb quarantine paddock for six months.
This is easier to manage if new arrivals are coming in over a short period of time. If new arrivals are coming in over a long time (high volume traders), there is a risk of creating a resistant worm hotspot, which could lead to super-resistant worms.
Earmarking quarantine paddocks for immediate spray-out and cropping is another possible solution.
After the quarantine drench and stand-off period, new arrivals should graze contaminated areas of the farm for at least a few days. This way, any resistant eggs that pass out will be diluted by the mixed worm populations already present.
Quarantine-drenched stock should never be run straight onto new grass or other low contamination areas.
