Wormwise Programme Manager Ginny Dodunski outlines the benefits of taking a targeted approach to pre-winter worm treatments in R2 and adult cattle.
For simplicity’s sake, it's tempting to run all older cattle through the yards before winter and give everyone a drench "just in case." But for R2 and adult cattle, the evidence suggests a more targeted approach is probably smarter and better for long-term drench resistance management on your farm.
By late April/early May, most R2 cattle will have well-established immunity to worms. The majority of well-conditioned, well-fed animals will carry relatively few worms in comparison to calves and be largely unaffected by larvae picked up while grazing.
Adult beef cows that have had a good summer and weaned in good condition, will generally carry even fewer worms.
R2’s and adults, although low shedders of worm eggs, can still act as a source of drench-susceptible worms, (refugia) that can help ‘dilute out’ drench resistant worms being passed by calves.
R2’s in particular, can frequently be passing a few worm eggs, and when people have looked, these are often a mix of Cooperia and Ostertagia. This means having undrenched R2’s sharing a grazing area with calves, can be very helpful. The R2s consume more worms than they put out but can re-populate paddocks with a mix of ‘good’ worms as they go. But only if you don’t drench them all!
Farm system matters too. Those undrenched R2s are relatively more important in a system that only carries calves and R2s. Beef breeding systems are generally low worm risk, especially where adults outnumber young stock or where the operation is part of a mixed system with sheep and/or deer.
The key question for R2 and adult cattle heading into winter is not "should I drench the whole mob?", but rather “which individuals actually need treatment?”
So, what to do?
Faecal egg counts are generally a poor guide to the impact that worms may or may not be having on older cattle. Instead, focus on body condition and recent weight gain performance, as well as visual ‘bloom’ of animals, when deciding who to treat in late April/early May.
Lighter, poorer animals within the mob are the most likely candidates for treatment at this time of year. This is true for R2 finishing cattle/bulls, heifers who have weaned their first calf (although you may treat a higher proportion on this basis), and adult cows.
And what to treat with?
If treatment is warranted, an injectable drench containing a mectin drug is the recommended choice for these age groups. Mectin drenches given via the injectable route achieve higher blood levels of drug, as well as higher concentrations within Ostertagia worms — which can burrow into the abomasum lining and sit very close to blood vessels.
Cooperia may still form part of the worm population in R2 cattle, especially if for some reason the animals have had a hard time and are behind their weight targets (relatively less mature). For these cattle, a combination containing levamisole is more likely to remove Cooperia.
If you use oral drenches on bigger cattle and are happy doing this, don’t change, just make sure your drench contains a mectin component. Avoid pour-on formulations. These have the lowest and most variable absorption.
What about adult dairy cows? (You weren’t expecting that now were you!)
Production responses from treating adult dairy cows for worms are not guaranteed. Studies on milk production responses show a positive response overall, but with very wide variation between individual cows and herds.
Risk factors that may increase the likelihood of a worthwhile response include: cows sharing grazing with calves from December to May, especially in summer-wet areas or under irrigation, and underfeeding.
First lactation heifers are more susceptible to worms than mature cows and, like the R3 beef heifers, a relatively higher proportion of this age group may benefit from treatment.
No New Zealand trial work has shown a reproductive benefit to treating adult dairy cows.