Triple combination drenches have been the backbone of healthy, productive sheep for a long time.  These drenches have typically contained abamectin, levamisole and albendazole. 

More sheep in Australia get treated with a triple combination drench than any other type of drench¹. 

However, new triple drenches containing moxidectin, rather than abamectin, may risk accelerating drench resistance development.   

Risk of persistency 

Persistency of an anthelmintic treatment is highly valued during times of the year when worm challenge is high and sheep have low immunity to worms.  Often, they make the difference for a successful lambing or a summer rescued from barber’s pole worm. But their risk of accelerating drench resistance has long been understood.  

Every time we expose parasites to an anthelmintic treatment, we are applying selection pressure to the worm population. 

Worms surviving treatment able to add their genes for resistance to the population. Drugs with persistency allow this proliferation of resistance to continue unencumbered by the reestablishment of susceptible worms. 

To reduce this effect, persistent drenches can be administered at the same time as drench actives from different chemical classes to remove as many adult worms as possible.  

However, worms with resistance can re-establish during the period of persistency, allowing them to reach maturity and egg laying capacity earlier than susceptible worms.  

Just as we don’t want a neighbour’s ram to get a two-week head start in our ewes, persistency gives the development of resistance a start that we don’t want. 

The risk of persistent drenches can be exacerbated during times when there is less refugia on pasture, for example over summer or when sheep are moved onto prepared pastures. 

We can manage this risk of persistency through various exit-drench strategies when we selectively use them at key moments of the production cycle. But if we use them frequently, our ability to manage the negative effects of persistency is limited. 

Triguard Triple Combination Drench for Sheep, with abamectin, delivers the potency of the macrocyclic lactone (ML) family of drench actives, but without the persistency of moxidectin. 

Risk of residues 

Ewes over the lambing period are often regularly treated due to the risk  worms pose to their health and their role in contaminating pastures for their lambs. 

Using a triple combination drench to treat ewes pre-lambing and, if required, again at lamb marking, is a common strategy to control worms during this period.  

However, research has demonstrated  orally administrated moxidectin is carried over into the ewe’s milk and has been detected  in the plasma of suckling lambs². 

Moxidectin drug exposure via milk can increase the development of resistance as it has been shown to select resistant populations of worms in lambs challenged with known resistant and susceptible strains³.  

While all macrocyclic lactones can be detected in milk following treatment, the exposure to suckling lambs is greatest for moxidectin because of its persistence profile and lipophilic properties. 

Compared to other macrocylic lactones, moxidectin in milk is detected at higher levels and for longer⁴, indicating that triple combination drenches with abamectin are a more appropriate drench for ewes pre-lambing or at lamb marking. 

Using abamectin in the Triguard triple combination, minimises the risk of ML exposure in suckling lambs compared to moxidectin based drenches, offering a valuable tool to control worms in lambing ewes. 

Keeping your triple drench working 

Triguard has been trusted since 2010. To keep the drench working into the future, here are few things that you can do to help prevent resistance. 

• Have a good quarantine induction protocol in place. Include monepantel or derquantel in your quarantine treatment along with three additional chemical classes. 
• Correctly weigh your sheep and calibrate your drench guns. Drench sheep in similar size ranges to the heaviest in the mob. 
• Minimize the number of drench treatments needed on farm through the use of strategic treatments and grazing management. 
• Use worm egg counts to assess the need for tactical treatments.  
• Only drench onto clean pastures for lambing ewes and weaners. Don’t make it a routine habit for all stock. 

References 

¹ AVcare data MAT Q2 2024 

²  Campbell, B.J., et al., (2017) An investigation of oral moxidectin carryover to nursing lambs via milk. Small Ruminant Research 154:9-12 doi.org/10.1016/j.smallrumres.2017.07.001. 

³ Leathwick, D. M., Miller, C. M., & Fraser, K. (2015). Selection for anthelmintic resistant Teladorsagia circumcincta in pre-weaned lambs by treating their dams with long-acting moxidectin injection. International Journal for Parasitology: Drugs and Drug Resistance, 5: 209-214. 

⁴ Imperiale, F., Lifschitz, A., Sallovitz, J., Virkel, G., & Lanusse, C. (2004). Comparative depletion of ivermectin and moxidectin milk residues in dairy sheep after oral and subcutaneous administration. Journal of dairy research, 71: 427-433.