The Power of Refugia

Known as refugia, the term can be mystifying, but basically involves creating a refuge of parasites that are non-exposed to drench, says Zoetis veterinary operations manager and veterinarian Clive Bingham.

A sustainable parasite management plan involves two aspects: firstly, controlling the level of parasites on your farm, and secondly, trying to control drench resistance. Refugia is the number one tool available to farmers in slowing the latter.

“The reason for practicing refugia is that we want to have the genetics for susceptible worms maintained within the overall worm population.”

Bingham likens it to breeding an animal. When selecting the genetics for growth rates in lambs, for example, farmers want to combine the best ram with the best ewe to achieve genetic gain. Worms are no different.

Simply put, farmers need to mate resistant worms with susceptible worms, to dilute the resistant genetics down.

“If we wanted to make resistance worse, we would mate resistant parasites with other resistant parasites within the animal, that’s what we encourage when we drench animals with ineffective drenches. If we kill all the susceptible worms, the only ones left are the resistant ones. If we want to slow that down, we need to do the opposite.”

How to use refugia

Implementing refugia as part of an integrated parasite management plan is relatively straight forward, but requires a different approach for adult and young stock, Bingham says.

“For adult ewes, it’s really quite simple. Rely on nutrition to allow the animals to manage parasites for themselves. Use nutrition as much as you can, as adult stock have their own immunity.”

In simple terms, ideal management looks like not drenching anything. However, in practice, there may be some adult ewes that do need drenching, so it’s about minimising inputs and not drenching everything.

Bingham encourages farmers to work on the bottom or tail end ewes, based on Body Condition Score (BCS), and treat only those poorer animals that need it.

“Most ewes should be in good condition, and they will add refugia or susceptible parasites onto your farm.”

For young stock, lambs for example, it is trickier. For the first few months of their life, lambs do not have a fully developed immunity to worms.

Developing immunity is largely based on weight. “We know if we grow lambs on mum faster, they develop immunity quicker and are more robust going forward. Weight is an important factor.”

Best practice says it would be nice not to drench anything, but in reality, lambs will likely require drenching.

“If there is a high parasite challenge, most farmers want to drench everything. That’s fine, but they need to take other steps to introduce susceptible parasites into the system.”

The easiest way to add susceptible parasites is to use undrenched stock of a different class, such as adult ewes on lamb finishing areas or older cattle where yearling cattle are grazed.

“Follow lambs with undrenched ewes to dilute the resistant worms with susceptible ones. You could also run cull or poorer condition ewes amongst the lambs, leaving them undrenched but getting fed well.”

A second way to add susceptible worms, when you do not have any adult stock, is to not drench all the animals within a mob. This can work well for cattle where you are monitoring individual weight gain on a monthly basis, but can be more challenging for lambs. It is also a technique that a lot of farmers are reluctant to implement.

Finally, there is the third, but probably less effective method of adding refugia, which is extending drench intervals.

“There is a risk associated with the last two techniques. You really need to have the lambs on low contamination areas and you must have a monitoring system in place.

“If you are solely lamb finishing, it’s not sustainable on pasture alone. You need to introduce adult ewes or put in crop. Those farmers who finish lambs, more and more are moving towards crops and starting to adopt that. For the guys who can’t have crops, it’s building a system around breeding as much as possible and going store. Getting lambs off as soon as possible is the way to go.”

In the case of dairy grazing, for example, running only young stock significantly reduces the potential to create refugia. R1 cattle will need more drench, so R2 cattle must be given minimal to no drench to balance this out, and they must be run on the same areas as the R1s have been.

Farm Without Worms

While Refugia is not a difficult concept, Zoetis veterinary operations manager and veterinarian Clive Bingham emphasises that it is just one part of the parasite equation.

Refugia must be considered within the overall farm system and should be part of an integrated parasite management plan that takes into account the entire Wormwise ‘FARMED’ acronym of Feed, Avoidance, Refugia, Monitoring and Effective Drench.

“Focus on minimising your use of drench. Drench is your selection for resistance, so use it only on those classes of stock that really need it and only when it is required.”

For Bingham, it is about farming with worms to minimise their impact. The goal is to have as low a number of worms as possible, while ensuring they are as susceptible as possible.

“If you manage your parasites better, you get better performance out of your stock. Good pasture management is also good parasite management, they go hand-in-hand.”

• Article supplied by Zoetis