Timing your first calf drench could make or break your herd's health this season—get it wrong, and you might be fighting an uphill battle against parasites that stunt growth and drain profits!
With a bumper crop of calves hitting the pastures this year, Wormwise vet Mary Bowron is here to guide us through the tricky question of when those young ones should get their inaugural drench. And this is the part most people miss: it's not about sticking to a rigid calendar; it's about smart, evidence-based decisions that protect your animals without unnecessary treatments.
The golden rule? Hold off on drenching until there's actual evidence of worms that need tackling. For parasites to take hold, calves must have a functioning rumen—think of it as their digestive engine that's just starting to rev up—and be munching on grass regularly. Beginners, imagine the rumen as a fermentation vat in the calf's stomach that breaks down tough plant fibers; without it fully operational, worms can't thrive in the same way.
Typically, you won't need to intervene until they've been grazing substantial amounts of grass for about three to four weeks. To pinpoint the perfect moment, grab some fresh fecal samples and send them for fecal egg counts. If the results show zero eggs, no drench is required yet—simply recheck in a couple of weeks. But if eggs are detected, consult your vet to gauge whether the count justifies immediate action or another test in a week's time. For a deeper dive, check out the Wormwise website's section on interpreting fecal egg counts (https://beeflambnz.com/knowledge-hub/blnz-wormwise-programme/worm-diagnostics/interpreting-faecal-egg-counts)—it's a fantastic resource that explains how to read these results like a pro.
Once you've decided it's time, choose your drench wisely. Opt for something effective, preferably an oral combo product that targets multiple parasites. Don't skip calibrating your drench gun and weighing a sample of calves to ensure accurate dosing—over- or under-dosing can lead to resistance or wasted effort.
Here's where it gets controversial: many farmers swear by routine drenching every 28 days, but is that really the best approach, or does it breed resistant worms? We say test first to avoid overuse.
It's crucial to verify that your chosen drench is doing its job. Ten days post-treatment, collect another set of ten fresh samples for a fecal egg count. Ideally, it should read zero. If not, seek expert advice pronto. And here's a sneaky detail: if past drenches haven't worked well, new calves might already be picking up resistant L3 larvae (the infective stage of parasites) that survived the winter from previous seasons' herds.
Minimizing larval intake is key to keeping growth on track. Picture this: calves gobbling up high numbers of larvae daily lose their appetite, eating less grass and falling behind. If you're reusing the same paddocks year after year, the risk skyrockets—calves act like parasite factories, pumping larvae back into the soil.
For pastures potentially loaded with parasites, consider these proactive steps:
- Keep supplements flowing post-weaning to ease the transition; bonus, 'worm-free' feeds add an extra layer of protection.
- Rotate grazing with minimum covers of 1800kg DM/ha. Parasite larvae lurk at the base of the grass, so taller swards reduce exposure to those pesky L3 larvae.
- Offer alternative grazing spots, like areas recently used by cows. Adult cows shed fewer eggs and act as natural cleaners, sweeping up larvae and leaving pastures safer.
But here's where it gets controversial again: some argue that moving calves to cow pastures disrupts farm efficiency, while others see it as a game-changer for parasite control. What's your take?
If you've drenched effectively yet calves still seem off, rule out coccidiosis. Even without obvious symptoms like straining, bloody diarrhea, or poor thrift, subclinical issues can lurk. Like parasite eggs, coccidia build up in repeatedly used calf paddocks. Since calves often get coccidiostats in the shed, extending that protection during the paddock shift can smooth the transition.
After that first drench, what's the plan? Old habits might have you dosing every 28 days blindly, but let's rethink that. Instead, check fecal egg counts 28 days later. If levels are low, wait and retest in one to two weeks rather than rushing to drench.
That 28-day count also reveals pasture contamination levels. A sky-high result? Drenching is probably worthwhile. The strategies above can dial down that risk quickly.
Stay tuned for our next e-diary piece on long-term parasite management in calf rearing—it's packed with sustainable tips to keep your system thriving.
For more insights:
- Wormwise dairy factsheet (https://beeflambnz.com/knowledge-hub/PDF/wormwise-dairy.pdf) (PDF, 1.2 MB)
- When should I start drenching my calves? (https://beeflambnz.com/knowledge-hub/video/when-should-i-start-drenching-my-calves)
- Parasites in calves (https://beeflambnz.com/knowledge-hub/video/parasites-calves)
Do you stick to targeted drenching based on tests, or do you prefer a more traditional schedule? Is pasture rotation a must-do in your operation, or does it complicate things too much? Share your experiences and opinions in the comments—we'd love to hear if you agree, disagree, or have a counterpoint to these strategies!
