Exit drenching supports sheep who may have parasites partially or fully resistant to active ingredients in previous drench products.

It seems like there is no such thing as just drenching sheep anymore; with terms like knockout drench, exit drench, strategic drench, trigger drench, and quarantine drench all becoming more common in our vocabulary.

At this time of the year, exit drenching is the term that we need to be thinking about the most. The idea behind exit drenching is that animals which were treated with a long-acting drench prior to lambing are likely to be approaching the end of the payout period of that product. There is a chance that these ewes are now harbouring parasites that are partially or fully resistant to the active ingredient (or ingredients) of the long-acting product. We do not want these parasites to continue producing eggs which are going to contaminate the environment where the lambs are grazing.

Parasite resistance is a highly complex issue, with many factors that can lead to resistance on any property. One such counter method would be to use an exit drench in the hoggets and ewes that were treated with a long-acting product. The theory is that a different set of active ingredients will remove any parasites which have survived during the use of the long-acting product. Once the majority of parasites are removed by the drench, the immune system will be better able to control incoming larvae. The immune system is generally better at stopping developing larvae than it is at removing adults. If a long-acting injection of Moxidectin has been used then an ideal exit drench would contain a combination of a white and clear, and a triple or novel drench is likely to be effective. In a perfect world, the farmer would know which active ingredients or products are 100 per cent effective on the property and use this information to select the exit drench product. In the absence of this information, using a triple active product such as TrivOX, TrivAL or a novel product is likely to give you the highest chance of being effective.

Alternatively, if a white/mectin combination capsule has been used, then the exit drench will need to contain levamisole (clear drench). Due to the amount of resistance already identified around New Zealand, the best product for an exit drench here is going to be a triple active such as TrivOX, TrivAL or a novel product again. The same rules apply to an injectable product; knowing the drench resistance status on the property makes selecting the active ingredients or product a much easier task.

Tracking faecal egg counts is another method that can help to stop resistance from developing as a result of long-acting drench usage. As animals are approaching the end of the payout period, sequential egg counts can be carried out. If eggs are seen in the faeces this may trigger a drench to be given to the group. As drench products can inhibit egg-laying, without necessarily killing parasites, using this method can miss some indication of developing resistance.

Knowing the full resistance status of your property is well worthwhile and running a faecal egg count reduction test every 2–3 years helps farmers know what is going to work best on their farm. Despite the upfront cost of running this test, the information gained can make a significant change in farm profitability especially if there is developing resistance on the farm.

For further information, contact your Farmlands Technical Field Officer or the friendly team at your local Farmlands store. Article supplied by Donaghys.