TL;DR: Beef + Lamb NZ emphasises quarantine drenching for new stock to combat drench-resistant worms, advocating for strategic treatment and management practices to maintain effective farm drench status and prevent resistance spread.
Ginny Dodunski of Beef + Lamb New Zealand’s Wormwise program underscores the critical need for a quarantine drench protocol for new farm arrivals like lambs and calves. This step is crucial to prevent the spread of drench-resistant worms, especially when the drench-resistance status of replacement ewes is unknown.
For sheep, the optimal quarantine drench involves a mix of Zolvix or Startect and a Benzimidazole (BZ)/Levamisole drench, administered simultaneously yet separately. For calves or R1 cattle, Zolvix, paired with a BZ/levamisole combination, is recommended. The Wormwise site offers alternative suggestions and specifies drenches unsuitable for quarantine purposes.
Dodunski emphasises the protocol’s significance, highlighting that drenches eliminate adult worms and larvae but not eggs. Thus, eggs may continue to be expelled for up to three days post-drenching.
Post-drenching, it’s advised to keep the stock on a hard surface without grass, like a yard or grating, with adequate food and water for 24-48 hours. This prevents the eggs from hatching into larvae, as they lack the necessary moisture and grass to survive.
Alternatively, newly arrived stock could be kept in a designated quarantine paddock for the same duration. This paddock should not be grazed by the same stock class for several months to prevent creating a resistant worm hotspot.
Marking quarantine paddocks for immediate cropping is another solution. After the quarantine period, it’s vital to expose new arrivals to contaminated farm areas to dilute any resistant eggs with existing worm populations. Quarantine drenched stock should avoid grazing on fresh grass or low contamination zones to prevent the spread of resistance.
This approach ensures that farms maintain effective drench status and protect against the spread of resistant worms, combining careful quarantine measures with strategic grazing management.