Cattle Drench Concerns: Expert Urges Farmers to Check Efficacy Amid Rising Resistance

In New Zealand, dairy farmers face growing challenges with calf drenches as resistance to these treatments increases among worm species. Recent surveys of cattle drench resistance show concerning results, with worms displaying resistance even to double and triple drench combinations.

Wormwise Programme Insights The Wormwise programme manager, Ginny Dodunski, stresses the importance of checking the performance of calf drenches. Her recommendations come after data revealed that the common intestinal worm, cooperia, showed resistance in 56% of tests, and the more severe ostertagia demonstrated resistance in 34% of cases. This data, albeit limited, aligns with reports from veterinarians who deal with intensive cattle systems across the country.

Expert Advice Dodunski emphasizes that farmers should not assume that combination drenches eliminate all worms. Instead, she advises checking drench performance and finding ways to reduce worm challenges in young cattle. "Good nutrition and low worm intake are more effective than regular drenching," she advises.

Survey Findings Tests conducted between 2021 to 2024 across New Zealand reveal significant resistance among common worm types to well-used drench products. Resistance to the mectin family, a long-time staple for ostertagia control, is also evident, with 45% and 50% of tests showing resistance to oral triple combinations and abamectin/levamisole injections, respectively.

With a possible risk of R2 dairy heifers carrying untreated ostertagia, and the threat of clinical ostertagiasis in adult cattle, Dodunski warns of the potential return of this once-feared ailment. "Farmers should remain vigilant and keep assessing their calf drenching strategies," Dodunski concluded.