It’s a common rule of thumb to worm horses at the change of each season.

Autumn rolls around, and it’s time to treat. Then again in winter, spring and summer – simple, routine, and easy to stick to.

While that approach is largely correct, it can lead to some parasites being missed and may also increase the risk of resistance over time.

Moving from autumn into winter, things can feel like they’re slowing down. Pasture growth drops off, temperatures cool, and overall activity seems lower.

But parasite pressure doesn’t disappear – it just changes.

Some worms persist on pasture, while others remain inside the horse in different stages of their lifecycle. So even if you’re not seeing obvious signs, there can still be a burden there ticking along in the background.

During autumn, and into winter, the key worms to watch for are small strongyles, tapeworms and, in some cases, roundworms – each behaving slightly differently as conditions cool.

Which worms’ matter through autumn and winter?
Small strongyles are one of the biggest considerations at this time of year. Over the cooler months, they can sit in an encysted (dormant) stage within the gut lining. They’re not always causing obvious issues immediately, but they can build up and emerge later.

Roundworms tend to be more of a concern in younger horses but are still worth keeping in mind depending on your age groups.

Tapeworms are a bit different again. Unlike strongyles and roundworms, horses don’t pick up tapeworms directly from pasture. Instead, they’re infected by ingesting small pasture mites (oribatid mites) that act as an intermediate host. This means their lifecycle is slower and more seasonal, and they tend to build up over time rather than spike quickly.

Because of this, tapeworms are often targeted at specific times of year – with autumn being a common point to address them.

Why product choice matters
To target encysted small strongyles, actives such as moxidectin or specific fenbendazole programs are commonly used.

For tapeworm, actives such as praziquantel or pyrantel (at the correct dose) are typically used, often as part of an autumn treatment.

For roundworms, particularly in younger horses, actives such as fenbendazole or pyrantel may be used depending on the situation.

For broader parasite control, combination actives may be used where multiple parasites are being targeted at once.

During the autumn to winter period, the focus is often on managing existing burdens and targeting parasites that persist through cooler conditions.

This is where products such as iO Fenbender, iO Equiduo Liquid and iO Blade can play a role within a broader worming program, as they contain actives suited to targeting common parasites during this time of year.

Product choice should always be guided by what you’re looking to target, along with faecal egg counts, seasonal conditions and your overall worming approach. If you require further assistance, consult your local veterinarian.

Across Australia, internal parasite control in both sheep and cattle is changing. The shift toward triple-active (“3-way”) drenches is not driven by marketing or fashion, but by necessity. On many properties, single- and dual-active drenches no longer provide reliable or predictable control.

Anthelmintic resistance is now well established in sheep parasites and is increasingly recognised in cattle systems. Resistance already exists at low levels in most worm populations. Drenching does not create resistance; it selects for resistant worms. Once resistance becomes established, it does not reverse. This has forced a change in how drenches are selected and why combination products now sit at the centre of modern parasite control programs.

Why triple actives work
Triple-active drenches combine three unrelated chemical families, typically a macrocyclic lactone, a benzimidazole and levamisole. Each attacks worms in a different way. For a worm to survive treatment, it must already carry resistance to all three actives at the same time.

This is the key advantage. Field experience and modelling show that combination drenches dramatically reduce the number of worms that survive treatment compared with single-active products. Triple actives are effective against susceptible worms and against populations with single or dual resistance, which now describes many Australian sheep flocks and is increasingly relevant in cattle, particularly for Cooperia and other gastrointestinal nematodes. When used appropriately, they also slow the rate at which resistance genes accumulate in the worm population.

Low-volume triple-active formulations add a further practical benefit, particularly in cattle. Accurate dosing is easier, under-dosing is less likely, and consistency across variable liveweights improves. Given that under-dosing is a well-recognised driver of resistance in both sheep and cattle, this alone is a meaningful advantage.

What triple actives do not do
Triple-active drenches are not a silver bullet. They do not remove resistance risk, replace management, or justify routine blanket drenching in either species.

Misuse can still accelerate resistance. Frequent whole-mob treatments, drenching when worm burdens are low, repeated reliance on the same combination, or moving stock immediately onto low-contamination paddocks all increase selection pressure. These principles apply equally to sheep and cattle, even though clinical disease may be less obvious in adult cattle. Triple actives are powerful tools, but they remain tools, not strategies.

Refugia – the concept that protects drench life
Refugia refers to the proportion of the worm population that is not exposed to a drench at the time of treatment. This includes worms in untreated animals, eggs and larvae on pasture, and life stages not affected by the product.

Refugia matters because susceptible worms dilute resistant survivors after drenching. When refugia is large, resistance develops slowly. When refugia is small or eliminated, resistance develops rapidly. Preserving refugia is the single most important factor in slowing resistance, regardless of which drench is used.

Why faecal egg counts matter more than ever
Faecal egg counts (FECs or WECs) underpin evidence-based parasite control in both species. They answer two essential questions: is treatment needed, and did the treatment work?

Pre-drench testing helps avoid unnecessary treatments and preserves refugia. Post-drench egg counts, or formal faecal egg count reduction tests, confirm whether a drench remains effective on a property. Without post-treatment checks, resistance can develop silently until control fails.

Some retailers now offer egg counts before a sale. The next step is normalising post-treatment follow-up, particularly in cattle systems where resistance can be overlooked until production losses occur.

Looking ahead
The move to triple-active drenches reflects a broader shift away from product-led decisions toward system-based parasite management. The future lies in combining appropriate chemistry with testing, refugia management, grazing decisions and informed advice.

Used thoughtfully, triple-active drenches protect sheep and cattle performance today while buying time against resistance tomorrow. That balance — productivity now and sustainability long term — is the real power of three.

Across many Australian sheep-producing regions, autumn marks a period when internal parasite burdens can begin to build. After months of warm conditions and grazing pressure, worm populations on pasture may reach levels where they begin to affect flock performance.

Internal parasites are a constant challenge in grazing systems. Their impact is not always immediately visible, but over time they can reduce weight gain, compromise wool production and affect overall flock productivity. Understanding how worm burdens develop through the season is an important part of maintaining animal health and managing risk within a flock.

Why autumn is a key period for worm pressure

The lifecycle of most gastrointestinal worms relies heavily on environmental conditions. Warm temperatures and periods of moisture allow eggs passed in manure to develop into infective larvae on pasture.
As sheep graze, they ingest these larvae, allowing the cycle to continue within the animal. Over the course of summer and early autumn this process can lead to increasing levels of contamination in grazing areas.
By autumn, sheep may have been exposed to several generations of worms. This accumulation can result in higher parasite burdens within the flock, particularly in young or growing sheep that have not yet developed strong immunity.

Recognising the signs of worm burdens

The effects of internal parasites often appear gradually. In many cases the first signs are reduced productivity rather than obvious illness.
Producers may notice:
• scouring in affected sheep
• reduced weight gain or poor growth rates
• declining body condition
• dull or poor-quality wool
• reduced appetite or general thriftiness

Young sheep and lambs are typically more vulnerable, although adult animals can also be affected when parasite pressure becomes significant.

Managing parasite pressure in grazing systems

Effective parasite control rarely relies on a single intervention. Monitoring flock performance, observing pasture conditions and responding to seasonal changes all play a role in managing worm burdens.

Treatment decisions are often based on a combination of experience, observation and diagnostic testing. Faecal egg counts can provide useful insight into parasite levels and help determine whether treatment is required.

When treatment is necessary, worm drenches and vaccinations remain an important tool in reducing parasite burdens and supporting flock performance.

Treatment options within a parasite management program

A range of drench options are available to assist with parasite control in sheep. These products vary in their active ingredients and spectrum of activity, allowing producers to select treatments that suit their flock’s needs and the parasite challenges present on their property.
Choosing the right drench and applying it at the appropriate time can help reduce worm burdens and support flock performance. Treatment decisions should always consider seasonal conditions, parasite pressure and long-term resistance management.
Independents Own have selection of sheep worm treatments designed to support parasite control in Australian grazing systems. You can explore the Independents Own sheep worming range here

For further advice please consult your local veterinarian.

Internal parasites are a common challenge in grazing systems, particularly as seasonal conditions change. Worm burdens often build gradually, meaning the early signs can be subtle and easy to overlook.

Recognising potential parasite problems early can help producers respond quickly and minimise the impact on flock performance.

1. Scouring
   Scouring, or diarrhoea, is one of the most commonly recognised indicators of worm burdens in sheep. While scouring can have several causes, including dietary changes, persistent or widespread scouring within a mob can indicate the presence of gastrointestinal parasites.
2. Reduced weight gain
   Parasites compete with the animal for nutrients, which can reduce feed efficiency and growth rates. Sheep affected by worm burdens may appear slow to finish or may struggle to maintain body condition despite adequate feed availability.
3. Poor condition and thriftiness
   Sheep carrying significant worm burdens may show a general decline in condition. This can include weight loss, a dull fleece, or a lack of overall vigour.

Monitoring flock health
Because parasite challenges can develop over time, monitoring livestock condition and pasture pressure remains important throughout the grazing season. Diagnostic tools such as faecal egg counts can help determine whether worm burdens are present and if treatment may be required.

If producers suspect worm issues within a flock, a veterinarian can assist with advice on monitoring and parasite management options.

Seasonal conditions play a major role in the development of internal parasites in grazing livestock. For many sheep producers, autumn represents a period when worm burdens can begin to increase after several months of exposure on pasture.

Understanding why parasite pressure often rises during this time can help producers make more informed decisions about monitoring and treatment.

The worm lifecycle on pasture
Most gastrointestinal worms rely on pasture to complete their lifecycle. Eggs passed in manure develop into larvae that migrate onto surrounding pasture where they can be ingested by grazing sheep. Warm temperatures and periods of moisture provide favourable conditions for this development, allowing larvae to accumulate in grazing areas over time

Exposure builds through the season
By the time autumn arrives, sheep may have been grazing contaminated pasture for several months. This exposure can result in increasing parasite burdens within the flock, particularly where grazing pressure has been high or where young sheep are present.

Monitoring and management
Observation of livestock condition, pasture management and diagnostic tools such as faecal egg counts can all assist in identifying parasite challenges. Where treatment is required, a range of worm control options are available through rural retailers to help manage parasite burdens and support flock performance.

For further advice please consult your local veterinarian