Leaving 5% of lambs undrenched

By Andrew Dowling

Simple messages don’t work well in complex farm systems.  Refugia management is very important when it comes to preserving the life of drenches and there are several ways that this can be achieved.  Leaving some lambs (say 5%) undrenched is one method.  What impact will it have on your farm? This depends on your farm system and very importantly the efficacy of your drench.

Leaving a small number of animals undrenched to increase refugia only works if your drench is highly effective, so you need this information first.  The best way to determine this is by doing a drench efficacy test (FECRT) and analysing it by worm species.  A drench check is a great way to check that your drenching practice is effective but is not enough to create a plan to manage refugia with.  This is done by getting faecal egg counts (FEC) as the lambs are drenched and then taking individual samples again 10-14 days later.

You also need to gauge the effect of leaving some lambs undrenched both in reduced live-weight gain and how much impact they had on refugia. Identifying the undrenched lambs (eg. ear tags, raddle marking ) to monitor weight gain and faecal egg counts against they drenched lambs is very important.  Matching these results to weather data over several years will help to build a picture of what to expect in future years.  What works on your farm may not work for your neighbour.

So, my message it to talk to your animal health advisor before leaving every 20th lamb undrenched to make sure that you will be having a positive impact on the worm management on your farm.  Simple messages can be dangerous.