Wormwise vet Mary Bowron demystifies refugia and explains why it is an important tool for managing parasites.
The word refugia can be a confusing one. In general terms, refugia means ensuring there are some drench-susceptible worms available on your farm to reproduce. These susceptible worms need to significantly outnumber their drench-resistant mates.
Keeping a population of susceptible parasites on your farm slows down the development of drench resistance.
Without worms in refugia, drench resistant worms carry on breeding with each other, while susceptible parasites are killed by drenches. The resistant genes of the adult worms are passed on to their offspring, resulting in a growing population of resistant parasites. If left unchecked, over time the progeny of resistant worms become more dominant in the worm population and eventually, drenches fail to work. With one in three farms in New Zealand battling triple drench resistance, this is already a reality.
With no new drenches on the horizon, we need to be smarter about looking after the drenches we currently have and utilise other tools in the toolbox for managing parasites. Refugia is an important tool you should implement.
Refugia exists in two places in your farm system: either on pasture, as susceptible larvae,or inside animals as susceptible adult worms. Susceptible adult worms mate with each other in the gut of the animal and breed more susceptible progeny.
Over 90 percent of the parasite population is in the environment, so looking at ways to influence worms on pasture is essential. With refugia, we are aiming to maintain a population of susceptible worms on pasture so when animals are grazing, they are more likely to ingest susceptible infective L3 larvae than drench-resistant ones.
There are three fundamental strategies to create refugia.
Firstly, having younger animals share grazing areas with older, undrenched animals. This could be applied using well-conditioned, well fed, undrenched adult ewes or cattle to graze pasture previously grazed by drenched lambs/calves. This is one of the most effective ways to create refugia. Mature animals have developed a level of natural immunity to parasites, so drenching is typically not necessary.
Alternatively, you could graze undrenched light ewes with lambs. By not drenching these ewes, refugia is provided and the improved nutrition will help the ewes gain body condition prior to tupping. A great tool to use after weaning.
Secondly, where feasible, extending drench intervals can allow more time for susceptible worms to breed with both resistant ones and each other, to slow down the production of ‘resistant-only’ worm progeny in young animals under regular treatment. With 28-day drench intervals, for three weeks in every four, only drench -resistant worm eggs are being deposited on pasture. Extending drench intervals reduces the reproductive advantage of the resistant worms.
However, extending drench intervals as a means of creating refugia requires close monitoring. It may not be suitable when Barbers’ Pole Worm is a risk or where young animals are grazing heavily contaminated pasture.
Monitoring is important to determine if a drench is required at 28 days, or if the interval could be extended. Factors to consider include FECs, demeanour and body condition of stock, feed available and grazing history. Extending drench intervals is easier when young stock are grazing areas with lower larval contamination such as new grass, crops, or pasture that has been grazed by another species for an extended period. Refugia is even more important in this situation to ensure resistant worms don’t dominate the worm population. If it is new permanent pasture, a light graze with undrenched adult stock before hand to seed the pasture with ‘good’ worms would be recommended.
Lastly, the option of leaving a proportion of animals undrenched at each treatment episode. This means selectively drenching of those animals that are smaller, not growing as fast or lighter in body condition.
The safest groups of animals in which to implement this approach are those that have well-developed immunity to worms. Examples include drenching only the poorer growing individuals in a winter lamb mob or only treating the bottom half of a group of two-year-old bulls. Or being selective when pre-lamb drenching ewes, targeting the light, multiple-bearing girls. Close monitoring of young undrenched animals is important to protect animal performance and not allow pasture contamination to build up.
Use of technology to implement and monitor refugia is an option. The Smartworm® app, used with an eID tag, utilises liveweight gain and other farm-related information to identify animals in real time that are most likely to require a dose of drench. The soon to be launched DAGI app helps to visualise refugia and pasture contamination by combining on-farm data and history and automated modelling to generate a heatmap of your farm. This enables grazing recommendations to avoid paddocks at highest parasite and resistance risk.
- Learn more about Using targeted selective treatment to reduce drench use (PDF, 876KB)
- Learn more about DAGI Combat Drench Resistance & Improve Flock Health.