Article Summary: Rotational grazing turns parasite control from a chemical firefight into pasture-based prevention. By moving stock after just a few days and resting paddocks for 30–60 days, infective larvae die off before animals return, sharply cutting reinfection. Layering mixed-species or mixed-age grazing, regular faecal egg counts, and targeted drenching keeps worm populations low, preserves drench efficacy, and lifts animal performance year-round.
Internal parasites may be too small to spot with the naked eye, yet they quietly erode animal health and farm profitability. Worms sap energy, reduce weight gain, and lower milk yields—costs that are often hidden until they become serious. By adjusting the way you manage pastures and stock movement, you can interrupt the parasite life cycle and keep burdens low without over‑reliance on drenches.
Why Continuous Grazing Fuels Worm Problems
When stock graze the same paddock day‑in, day‑out, they return to the dung patches they created only days earlier. Worm eggs in that manure hatch and develop into infective larvae that crawl up the pasture sward. Given enough moisture, those larvae are ready for ingestion within a fortnight. Continuous grazing, therefore, becomes a closed loop: animals shed eggs, the eggs become larvae, and the larvae are eaten again.
Over time, the larval population builds up faster than your animals’ immunity can cope. Young stock suffer first—showing weight loss, scours, or bottle jaw—but adult animals may also lag in production during high‑challenge periods such as warm, wet seasons. Because the paddock never rests, larvae rarely die off before the next mouthful of grass is taken. The result is a heavy, rolling infection that steps up each grazing season.
High stocking density compounds the issue. More animals mean more dung, more eggs, and more larvae per square metre. If minerals or feed supplements are fed on the ground, the contamination concentrates where animals congregate, accelerating re‑infection. Continuous grazing, therefore, sets the perfect scene for parasites to flourish.
Rotational Grazing: Rest Times That Work
Shifting to a planned rotation changes the equation. By moving stock off a paddock after a short graze—often three to five days—you limit the time they can pick up fresh larvae. Resting that paddock for 30–60 days (longer in cooler months) allows many of those larvae to die from exposure, desiccation, or simply running out of energy reserves before the animals return.
Length of rest is critical. Worm larvae of common species such as Haemonchus, Trichostrongylus, and Teladorsagia survive for different periods depending on temperature, moisture, and UV light. As a rule, hotter and drier conditions shorten their lifespan; cool, moist conditions extend it. Monitor local weather and adjust the rotation accordingly. In a wet summer, you might need a 50‑day gap, while a dry autumn could allow a 35‑day interval.
Short grazing periods also mean animals take the top layer of pasture first, where larval numbers are lowest, then leave before being forced to graze closer to the soil surface, where larvae cluster. That small adjustment alone can reduce intake of infective larvae by more than half. As an added bonus, longer rest periods promote pasture recovery, improved root depth, and higher forage quality.
Multi‑Species and Mixed‑Age Grazing Tactics
Parasites tend to be host‑specific. Cattle worms seldom infect sheep and vice versa. By alternating species on the same paddock, you dilute the parasite population. For example, sheep following cattle will ingest cattle larvae that cannot complete their life cycle, effectively vacuuming the paddock without adding to the sheep worm burden. Studies consistently report better lamb growth rates and lower faecal egg counts when sheep and cattle share a rotation plan.
Mixed‑age grazing delivers a similar benefit. Adult animals, with stronger immunity, can “clean up” a paddock before young, susceptible stock arrive. Placing ewes or cows ahead of lambs or calves on each move means the older group absorbs a higher proportion of larvae, leaving less behind for the younger animals.
You can also exploit pasture height. Goats browse higher, cattle graze mid‑sward, and sheep nibble lower. Managed well, a tiered system keeps overall pasture utilisation high while breaking parasite habitats. Just ensure that water points and shade are not overused, as cross‑species congregation can still allow some worm transmission through damp ground.
Measuring the Parasite Load: Faecal Egg Counts
Guesswork rarely pays when it comes to parasites. Faecal egg counts (FECs) give you a snapshot of the worm burden within a mob and reveal which classes of stock are under the greatest pressure. Collect fresh dung from ten to fifteen animals in a group, mix it, and send a composite sample to the lab. Results are expressed as eggs per gram (epg).
Regular FECs—every six to eight weeks during risk periods—let you track trends rather than reacting to vague signs of ill‑thrift. A sudden spike alerts you to revisit rest periods, consider a paddock spelling break, or dose a subset of animals. Conversely, a stable low count supports withholding treatment and maintaining refugia (a population of susceptible worms) to slow down drench resistance.
Keep good records. Matching FEC data to paddock history, weather, drench timing, and stock condition uncovers patterns that guide next season’s grazing plan. Over time, you will notice which paddocks stay “clean” longest and which need longer rest or alternative forage crops to disrupt the cycle.
Targeted (Selective) Deworming: Treat the Animals That Need It
Blanket drenching every animal on the same date is easy but costly—both in cash and in lost drug efficacy. Selective treatment uses FEC thresholds, weight gain data, and clinical signs to pick out individuals or sub‑groups that require a drench. By treating only those animals, you reduce chemical use, preserve drug effectiveness, and leave a refuge of susceptible worms in the pasture population.
In practice, choose a manageable sample size—perhaps the lightest 20 % of weaners—and drench only those that exceed a pre‑set egg count or lag behind growth targets. Follow up with a second FEC 10–14 days later to ensure the drench worked. An effective product should cut egg counts by at least 95 %. Anything less signals the early stages of resistance, prompting a change of drug class and a review of grazing pressure.
Remember, drenches are not a substitute for pasture management. Even the best product cannot keep up with daily ingestion of thousands of larvae. A robust rotation, informed by monitoring, keeps worm numbers low enough that strategic treatments remain effective for years, not seasons.
Year‑Round Integrated Parasite Management
Successful worm control hinges on stacking small, practical steps:
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Seasonal planning – Extend rest periods and tighten grazing durations during warm, wet months when larvae thrive.
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Pasture hygiene – Avoid feeding supplements on the ground; use troughs or feed pads to reduce contamination hotspots.
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Genetic resilience – Select breeding stock with naturally low FECs or demonstrated tolerance to parasites.
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Alternative forages – Chicory, plantain, and tannin‑rich legumes can suppress worm development and encourage faster live‑weight gains.
Apply these measures together and you build a system where parasites struggle to keep pace with management. Animals stay healthier, production lifts, and chemical costs drop.
Bringing It All Together
Parasite control is not about one big fix; it is the sum of many steady actions. Rotational grazing with meaningful rest periods forms the backbone, but success grows when you layer on mixed‑species grazing, routine monitoring, selective treatments, and sound pasture nutrition. By understanding how worms move between dung, grass, and gut—and by timing stock movement to break that loop—you take control of a problem that once seemed inevitable.
Start with a simple plan: map your paddocks, set a realistic rotation, and schedule the first round of faecal egg counts. Use the results to refine your approach each season. With a little observation and timely adjustment, you can turn parasite management from a constant battle into another well‑run part of your grazing system.
Until we meet again, Happy Biosecurity!
- The Dedicated Team of Pasture.io, 2025-04-22