Avoid drench resistance: A complete guide to effective sheep drenching

Mustering Sheep

Sheep drenching is common practice and is essential to maintaining the health and productivity of your flock. Parasites can cause significant weight loss, reduced fertility, and even death in severe cases – making it an incredibly important practice for anyone working with sheep and lambs. In this guide, we are exploring the different types of sheep drenches and best practices on how to drench sheep effectively.

What is sheep drenching?

Sheep drenching is the practice of administering a preventative treatment to your sheep and lambs to control internal parasites such as worms. Parasites are a major problem currently affecting the Australian sheep industry – in fact, they cost producers the most to control out of all the animal health issues that may afflict their livestock, including lice and flies.

The sheep drenching treatment is typically administered orally with a drench gun and can be applied to one sheep at a time, or in a group. The type of drench you use and the frequency of treatment will depend on a number of factors, such as local conditions and the parasite burdens present in the sheep. 

Shorn Sheap Shearing

Selecting from different drenches used to treat internal parasites

Before you begin the process of sheep drenching, you will need to select an appropriate product to control the kind of internal parasites you are dealing with. The effectiveness of a drenching treatment will vary based on the parasites it is being used to control, and the resistance of the parasites to the active ingredients in the drench. 

Common Australian sheep drenching products

Let’s explore some of the most commonly used sheep drenching products in Australia and which internal parasites they are designed to eradicate. 


Levamisole is a broad-spectrum anthelmintic (wormer) ‘clear’ drench that is effective against a range of mature and immature parasites, such as roundworms, nodule worms, and some tapeworms. 


This insecticide and anthelmintic is designed to control a range of internal parasites, including nematodes (roundworms) and gastrointestinal botflies. Abamectin works by paralysing the worm’s throat so it is unable to eat and subsequently dies. 


Albendazole is a broad spectrum anthelmintic from the benzimidazole ‘white’ drench family. It works by inhibiting glucose uptake in susceptible worms, which then causes them to lose energy and die. Albendazole is effective against a range of nematodes and cestodes (tapeworms). 


Moxidectin is an insecticide and anthelmintic that is effective against nematodes, particularly heartworms and intestinal worms, and gastrointestinal botflies. Moxidectin works by disrupting worms’ neurotransmission, which causes them to become paralysed and die. 


Ivermectin is a broad-spectrum anthelmintic and insecticide that can be used to eradicate a range of internal and external parasites, including gastrointestinal roundworms, nasal bots, and itchmite. 

Combination drenches

Combination drenches offer broad spectrum cover against parasites using a mixture of active ingredients designed to target resistance to one or multiple common types of drench. Resistance problems are growing rapidly, especially within certain sectors of the industry and in particular geographical regions, which means that combination drenches are skyrocketing in popularity as the only real solution to combating this increasing issue. A combination sheep drench may be formulated with any pairing of the above solutions, including levamisole, abamectin, and ivermectin.  

New generation drenches

These products are formulated using new research and development that has identified active ingredients that are not yet prone to resistance in sheep. These should be used in rotation with other combination drenches to prevent resistance from developing in your flock. 

It’s important to note that when selecting your sheep drench, you should consider a number of factors. These include the parasite species you are dealing with, the level of resistance of the parasites, and the local conditions, such as the environment, feed, and management practices. Some common types of internal parasite, such as the ‘barber’s pole worm’ (haemonchus) thrive in humid summer conditions, so may need multiple drenchings that season to remain under control.

How to drench sheep to avoid drench resistance

Drenching sheep in Australia can be complicated, especially as drench resistance becomes increasingly more common. In fact, drench resistance in sheep is so widespread that up to 90% of farms are now affected in some way. 

There are a number of drenches with single or more than one active ingredient that have shown evidence of resistance. 

Benzimidazole (BZ) ‘white’ drenches: Approximately 90% of sheep properties display some form of resistance to benzimidazole drenches when treating scour worms. 

Levamisole (LV) ‘clear’ drenches: Roughly 80% of properties display some resistance to drenches that solely employ this active ingredient (not in a combination drench). 

BZ and LV combination drenches: Approximately 60% of properties are resistant to this combination of active ingredients. 

Macrocyclic lactone (ML or mectin) drenches: ML drenches are now commonly resisted, with up to 70% of properties experiencing this when used singularly. 

Ivermectin drenches: Drenches using just ivermectin have experienced known resistance against teladorsagia (ostertagia) and haemonchus.

Moxidectin drenches: Up to 30% of properties have shown resistance to the active ingredient moxidectin when used by itself. 

Closantel drenches: Resistance to haemonchus is typical (up to 80%) in parts of New South Wales and Queensland when using this active ingredient alone. Many of these properties are also ML resistant. 

Triclabendazole drenches: This active ingredient is showing small signs of resistance strains when treating liver fluke. 

Naphthalophos drenches: Resistance to this type of drench is currently rare. 

If producers follow a drenching management strategy that avoids overuse of the same active ingredient or centres around a combination drench, resistance can be much easier to manage. Adopting a rotation strategy and understanding and keeping an eye out for signs of resistance can also help producers to avoid this problem. If you suspect your sheep are becoming resistant to a particular drench, it may be worth seeking professional advice to ascertain proof of resistance and subsequently stop using a drench that does not work. 

Father & daughter in front of sheep

How often should you drench sheep for best results? 

For best results in treating parasites, and to protect against potential resistance, sheep should be drenched between once and twice a year, depending on whether they are breeding or not. 

Based on the Australian climate, the first drench should be conducted in the summer season, usually around November or December. This coincides with an increase in some of the most common parasites at this time and ensures sheep will be best protected for the remainder of the season. All lambs should also be drenched for a second time when they are weaning, as they are much more susceptible to developing worms and other parasites at this pivotal time. The same principles apply to lambing ewes. Drenching will ensure lambs have the best chance of meeting developmental milestones and surviving through the season. 

Something important to note when planning a drenching strategy is that over-drenching will be ineffective. Instead of increasing your drenches, consult a veterinary professional to determine whether your sheep have developed drench resistance. 

The best sheep drenches to use

Now you know how to effectively drench your sheep for the best results, and which active ingredients to select to avoid resistance, you can choose your product or products. At Specialist Sales, we offer a broad range of drenches, including new-generation drenches which are less likely to see resistance in sheep flocks. 

New generation drenches

If your flock has developed a resistance to other drenches, new-generation drenches will be particularly effective. These offer a great option for most parasites and flocks. 

The Startect Broad Spectrum Oral Drench for Sheep is a short-acting, broad-spectrum combination sheep drench that kills the most damaging of worms, including those that are resistant to existing drenches. Startect contains a completely new active called derquantel that has no known resistance and is designed for greater sustainability, with each active protecting the others against resistance. When used routinely, Startect can also extend the life of older, more fragile drenches. 

Zolvix Plus Sheep Drench provides premium broad-spectrum control of sensitive roundworms in sheep, including strains with single, double, or triple resistance to white, clear, closantel and macrocyclic lactone drenches or their combinations. It is a combination drench that pairs monepantel, the only member of the amino-acetonitrile derivative (AAD or ‘orange’) class of anthelmintics, with abamectin. Zolvix Plus prolongs the life of all effective sheep drenches. 

Livamol with BioWorma is a nutritional supplement containing the natural biological control BioWorma, which captures and consumes infectious worm larvae, including chemical resistant or anthelmintic multi-resistant larvae, within the manure of grazing animals. This product is a non-chemical control for the free-living stages of grazing animals’ parasitic gastrointestinal nematodes (roundworms) which substantially reduces the number of larvae that can emerge from manure onto pastures. 

Combination drenches

We recommend using new-generation drenches in a rotation strategy alongside combination drenches, which include the following products. 

The Wolverine Combination Sheep Drench is a broad-spectrum drench that can be effective against internal parasites that are resistant to single actives. This product contains a high amount of closantel compared to single active closantel drenches. 

Avomec Dual Sheep Drench is used for the control and treatment of parasites like roundworm, nasal bots, itch mites, and mature and late immature liver fluke in sheep, with activity against resistant strains of barber’s pole worm (including strains resistant to both abamectin and closantel) and 6-week, sustained activity against closantel-susceptible barber’s pole worm (including strains resistant to macrocyclic lactones). 

The Tridectin 3-Way Oral Sheep Drench is a combination sheep drench that includes three powerful, broad-spectrum actives: moxidectin, albendazole, and levamisole. It is the only combination sheep drench in Australia to include moxidectin, the most potent of the ‘mectins’. 

Q-Drench Multi-Combination Drench for Sheep is a unique 4-way anthelmintic sheep drench that contains a powerful mixture of abamectin, albendazole, closantel, and levamisole. Q-Drench can be used to prevent the introduction of resistant strains onto a property and in a strategic worming program.

Finally, the Pole-Axe Sheep Drench is designed for the control of organophosphate-susceptible strains of mature and immature gastrointestinal roundworms in sheep and lambs. Pole-Axe has a different mode of action and must be used in a drench rotation program where resistance to the other drench families exists. Alternatively, it may be mixed with benzimidazole or levamisole-based drenches under veterinary advice. 

Helpful tips when drenching sheep

Before you begin your own sheep drenching process, here are a handful of helpful tips that will assist you along the way, and ensure you are conducting the most effective drench possible. 

Use a drench gun to drench sheep

Sheep drenching for internal parasites is typically done using a drench gun, which is a handheld device used to administer the liquid treatment to the sheep. One key benefit of oral drenching is that it can be done at any time and does not rely on weather conditions or environment. These treatments are also ready to use, meaning you can begin controlling parasites in your flock almost immediately after you observe any issues. 

Always monitor sheep regularly for parasites

Keeping an eye out for telltale signs of parasites will ensure you are prepared to employ a drenching strategy as needed at any point. Signs include weight loss, diarrhoea, and rough wool. Faecal egg counts are also a helpful tool for identifying sheep that are shedding a high number of parasitic eggs and can help you to determine when a drench is needed. 

Rotate your pastures

Rotating pastures can also help to reduce the number of parasites your flock is exposed to, as parasites are less able to survive on new, clean pastures. Shearing sheep annually and crutching can also help maintain the flock’s health against parasites and other health concerns such as blowfly strikes. 

Rotate your choice of drench

Of course, the number one tip to ensure sheep drenching remains effective is to rotate your drench to avoid resistance. You can also have a resistance test conducted on your flock before beginning treatment to identify the best course of action to take. 

Specialist Sales has been helping producers, both large and small, determine the best drench solutions for their flocks for more than 20 years. If you need more information or assistance with finding the best drench products and strategy for your circumstances, we are here to help – get in contact today. 

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