Rotational grazing, refugia & worm control

⚡ The short answer

Moving stock is not the same as controlling worms.

Rotational grazing can help reduce worm challenge. But moving livestock between paddocks does not automatically control worms.

Young animals rotating repeatedly through their own grazing area can gradually contaminate every paddock they use. And if those animals are being drenched regularly, the worms contaminating the pasture may increasingly be the ones that survived treatment.

So parasite-aware grazing asks more than how long has this paddock rested? It asks:

• Who grazed it last?
• How vulnerable were they to worms?
• How low did they graze it?
• What livestock grazed it afterwards?
• Were the animals drenched before they arrived?

Beef + Lamb New Zealand's Wormwise programme treats grazing management, refugia and drench use as connected parts of the same parasite system.

🌍 Where the worms are

Most worms are not inside the animal.

When we think about worms, we tend to think about the parasites living inside livestock. But much of the worm population on a grazing farm is actually outside the animal.

Worm eggs are passed in dung. They develop into larvae. Infective larvae move onto pasture. Livestock ingest them while grazing.

Wormwise describes roughly 85–95% of the total worm population as being on pasture, mainly as infective L3 larvae.

That changes how you think about control. Drenching kills worms in the animal. Grazing management influences the much larger population waiting outside.

📏 Grazing height

Where worm larvae sit in the pasture.

Larvae are not distributed evenly through the sward. Wormwise notes that many infective larvae are concentrated close to the soil surface and in the lower part of the pasture.

This matters because young animals forced to graze very tightly can ingest more larvae.

A practical principle is: keep vulnerable young stock eating mainly from the upper part of the pasture where possible. Wormwise recommends allowing lambs and calves to graze primarily the top third of the sward.

That can provide two benefits:

• lower parasite intake;
• better nutrition.

Those two things reinforce each other.

⚠️ Two problems at once

Grazing too low can cost you twice.

This connects parasite management directly with pasture management.

Graze too hard and you can leave:

• too little residual for fast pasture recovery;
• vulnerable stock eating lower in the sward where larval concentration may be greater.

So low residual → slower pasture recovery can occur alongside low grazing height → greater parasite exposure.

This does not mean longer grass is automatically worm-free. It means grazing height is part of worm exposure.

That is another reason rotational grazing should not be reduced to a fixed number of rest days — a point we make from the pasture side in rotational grazing for small farms.

🔄 Does rotation help?

Yes, potentially — but the details matter.

Imagine six paddocks used only by young lambs.

The lambs graze paddock one and contaminate it with worm eggs. Then paddock two. Then paddock three. Eventually they return to paddock one.

They have been rotating. But the whole grazing block has gradually become a young-stock parasite system.

Wormwise specifically warns that young stock rotating around their own block, without adult stock or another species, can build increasingly high pasture contamination.

So the important question is not simply "do I rotationally graze?" It is: what is happening to the worm population during the rotation?

⏳ Rotation length

Longer rotations can help — but don't use a magic number.

In general, the longer vulnerable stock take to return to the same ground, the lower the worm challenge may be.

Part of that reduction comes from larvae dying over time. But Wormwise says much of the benefit often comes from other stock classes or species consuming larvae in between.

This is important because pasture spelling alone is slow. Under typical New Zealand grazing conditions, Wormwise says meaningful reductions from time alone usually take months rather than weeks — in cool conditions it may take 3–6 months for larval numbers to fall substantially, while hot, dry conditions can reduce survival faster.

So a paddock rested for 30 or 60 days is not automatically parasite-safe.

🧭 Two separate questions

Pasture recovery does not equal parasite safety.

This is worth making explicit.

A paddock can be ready from a feed perspective while still carrying substantial parasite challenge. Likewise, a paddock can have rested for a long time and still contain infective larvae.

Ask two separate questions:

• Has the pasture recovered enough to graze? — that is pasture management.
• What worm challenge is likely to be present for these animals? — that is parasite management.

Good rotational grazing considers both.

🐏 Leader-follower

Let the vulnerable animals graze first.

One useful system is leader-follower grazing. The vulnerable animals graze first. For example lambs → mature ewes, or young calves → older cattle.

The young stock take the best-quality upper pasture. The less-susceptible animals follow and graze lower into the sward. Those follower animals can consume larvae without experiencing the same level of impact as vulnerable young stock.

Wormwise describes this as a useful way to reduce worm challenge while using pasture efficiently.

It also gives the vulnerable animals better feed, helping them grow toward the point where they can cope with parasite challenge more effectively.

🐄 Mixed species

Different species, different worms — but not sterilisation.

Different livestock species can also be useful. Many important worms are better adapted to one host species than another. So cattle grazing after sheep, or sheep grazing after cattle, can reduce the number of infective larvae available to the original host.

But do not simplify this to "cattle clean sheep paddocks." The biology is more complicated than that. Some parasites overlap between host species, and young animals of both species can be susceptible to their own parasite burdens.

The useful principle is: mixed-species grazing can reduce challenge, but it is not sterilisation. It works best as one part of a wider grazing plan.

🧬 Refugia

What is refugia?

Refugia sounds technical, but the concept is simple. It means maintaining a population of worms that has not been exposed to the drench.

Why would you want worms to survive?

Because many untreated worms are still susceptible to the drench. Those susceptible worms can mate with resistant survivors and help dilute resistance genes.

Without refugia, every treatment can increasingly leave resistant worms as the main population reproducing on the farm. Wormwise therefore describes refugia as an important strategy for slowing the development of drench resistance.

🌱 In practice

What refugia can look like on a real farm.

Examples include:

• undrenched mature ewes grazing areas also used by treated lambs;
• older animals left untreated where monitoring shows they do not need treatment;
• targeted selective treatment;
• longer drench intervals where safe;
• mixed stock classes sharing grazing areas;
• avoiding unnecessary treatment immediately before moving onto low-contamination grazing.

The exact strategy depends on the farm.

🚨 Drench-and-shift

The drench-and-shift problem.

This is one of the most important grazing–resistance interactions.

Imagine newly established pasture with almost no worm contamination. You drench a group of lambs. Most susceptible worms are killed. Any worms that survive treatment are more likely to carry resistance.

You then move those lambs straight onto the clean pasture.

The eggs contaminating that pasture now come disproportionately from the drench survivors. You have effectively given resistant worms an empty paddock to populate.

Wormwise specifically warns against routinely drenching and shifting onto clean grazing, including new grass and other low-contamination areas.

🌾 Clean pasture

"Clean pasture" can become a resistance hotspot.

Low-contamination grazing is incredibly valuable. Examples can include:

• newly sown grass;
• some forage crops;
• lucerne;
• plantain;
• chicory;
• pasture grazed by another species for a prolonged period;
• hay or silage aftermath.

But these areas need careful drench management. Wormwise warns that multi-year crops and newly established pasture can become hotspots for resistant worms if young stock are regularly drenched while grazing them — its page on forages and worms covers which forages help and how.

One strategy is to introduce some susceptible worms through undrenched older stock. Another is to monitor young animals and extend drench intervals when the actual worm challenge is low.

The key principle is: do not waste genuinely low-contamination grazing by turning it into a nursery for drench-resistant worms.

🧪 Monitoring

Use monitoring to protect low-worm grazing.

If animals are on genuinely low-challenge pasture or crops, they may not need treatment at the same interval used on permanent pasture.

Rather than automatically drenching at the expected date, Wormwise suggests using FEC monitoring to determine whether treatment is actually required.

For example:

• animals reach their usual treatment interval;
• they are still performing well;
• a FEC is low;
• treatment may be deferred;
• monitoring continues.

This creates less treatment pressure while preserving animal performance. Managing worms & drench resistance covers what a FEC does and does not tell you.

🌿 Conserved forage

Hay, silage and pasture aftermath.

Conserved forage can also play a role. Hay and silage themselves contain little or no meaningful worm larvae.

Pasture closed for hay or silage can also experience reduced contamination over time. After harvest, the regrowth may offer lower-challenge grazing than continuously stocked young-animal pasture. Wormwise identifies hay and silage systems as useful tools within parasite-aware grazing.

Again, "lower challenge" does not mean sterile. It means another useful management option.

❄️ Winter

Don't rely on frost to clean pasture.

Cold weather does not automatically reset parasite risk. Infective larvae do not all disappear with a frost.

In cooler conditions their metabolism slows, and survival can persist for months. Wormwise notes that cool conditions can allow larval populations to decline very slowly compared with hot, dry conditions.

That means winter rest is not the same thing as worm-free pasture. This is particularly important where young stock return to the same areas season after season — the point we made in Bulletin #2: Why frost won't save your paddocks from worms.

🔢 A worked example

A small-farm example.

Imagine a lifestyle block with six paddocks, ten lambs, several adult ewes, and a couple of cattle.

A simple rotation might be lambs → lambs → lambs → lambs around all six paddocks. That gives the grass rest. But every paddock is still being contaminated mainly by young sheep.

A more parasite-aware system might use lambs → mature ewes or cattle → pasture recovery → lambs later.

The lambs get the best upper pasture. Older or different livestock follow. The time before lambs return is extended. Some larvae die. Others are consumed by less-susceptible stock. And if the lambs do not need drenching every time they reach the next paddock, more susceptible worms remain in refugia.

No single step eliminates parasites. Together, the system reduces dependence on repeated drenching.

📝 Records

What should you record?

Useful grazing records include:

• paddock or grazing area;
• livestock class;
• species;
• entry date;
• exit date;
• rest period;
• pasture residual;
• previous grazing species / class;
• whether the animals were drenched before entering;
• FEC or drench-check notes;
• whether an area was newly sown or low-contamination forage.

That history can help answer:

• Which areas are repeatedly carrying young stock?
• How long before lambs return?
• Which paddocks are being used by adult stock between young-stock grazings?
• Did we drench before moving onto new pasture?
• Are treatment intervals changing?

🛠️ In the app

How My Block Hand can help.

My Block Hand can connect:

• herd and flock movements;
• paddock history;
• pasture rest periods;
• livestock treatments;
• drench products;
• FEC notes;
• animal weights;
• pasture observations.

The app cannot calculate how many worm larvae are on a paddock. But it can help you remember who grazed it, when they grazed it, what treatment they received and what happened afterwards. That is much more useful than trying to reconstruct an entire season from memory.

🚫 Mistakes

Common grazing mistakes in worm management.

Assuming rotation automatically controls worms. Young stock can contaminate every paddock in the rotation.

Treating rest days as a worm-safe countdown. Larvae can survive for months.

Grazing vulnerable animals too low. Lower grazing height can increase exposure.

Using only one young stock class. Adult animals or another species can help reduce challenge.

Drenching before every move. Treatment and grazing should not automatically be tied together.

Drenching directly onto clean pasture. This can strongly select for resistant worms.

Ignoring refugia. Eliminating susceptible worms gives resistant survivors a larger genetic advantage.

👣 Next steps

Practical next steps.

• Map where vulnerable young stock spend most of the year.
• Identify paddocks repeatedly grazed only by young animals.
• Use adult or alternate livestock where practical.
• Avoid forcing young stock to graze pasture too tightly.
• Separate pasture recovery targets from parasite-risk decisions.
• Use low-contamination grazing strategically.
• Avoid routine drench-and-shift onto clean areas.
• Monitor young stock with FECs where appropriate.
• Keep treatment and grazing records together.

✅ In short

Good worm management is a farm-system problem.

There is no paddock-rest number that makes worms disappear. There is no drench that permanently solves the problem. And there is no grazing system that means treatment will never be required.

The strongest approach combines healthy animals + good nutrition + thoughtful grazing + monitoring + refugia + effective drench when needed.

The aim is not to eliminate every worm from the farm. It is to keep parasite challenge low enough that livestock perform well without selecting so aggressively that the drenches we depend on stop working.

📚 Further reading

Where this page's guidance comes from.

Beef + Lamb New Zealand's Wormwise programme is the primary authority used throughout this guide:

• Wormwise programme overview — the whole system: nutrition, grazing, monitoring, refugia and drench.
• Worms on pasture — where the 85–95% figure and the larval-survival timeframes come from.
• Grazing management — leader-follower, mixed species, rotation length and young-stock blocks.
• Forages and worms — low-contamination grazing, crops, and the resistance-hotspot warning.
• Refugia — leaving some worms unexposed to drench, and the ways to achieve it.
• Worm life cycle — egg to larva to infective L3, which is what the rest period is actually acting on.
• Research papers and additional tools — where the Wormwise handbook and the supporting research sit.