Quarantine treatments for all in-coming sheep. Not all farms have resistant worms so quarantine treatments are vital to ensure that any in-coming sheep don’t bring resistance with them. Find out more here.
Administer drenches correctly and at the right dose rate. Always dose to the heaviest in the group and check the dosing gun is working properly by discharging it several times into a syringe or measuring jug. Make sure the drench goes over the back of the tongue. Find out more here.
Test for resistance. Find out which drenches are working effectively on your farm by taking dung samples before treatment and again a set number of days afterwards. Use this information to plan a strategy that takes account of your current resistance status with the aim of maintaining the effectiveness of the chemical groups that are still working. Find out more here.
Reduce your dependence on anthelmintics where possible. Look for ways to use other strategies, such as grazing management and good nutrition to reduce worm burdens. Find out more here.
Try to use anthelmintics only when necessary. Faecal egg count (FEC) monitoring helps to determine when and which sheep to drench. Sheep farmers who regularly take FECs use less drench and so reduce the selection pressure for resistance. Minimising the treatments given to mature sheep that are immune to most worm species is also important. If adult sheep are fit and healthy, the need to treat them is limited, meaning routine treatments such as ewes pre-tupping avoided for the majority of the flock. Find out more here.
Select the most appropriate anthelmintic. Monitoring can also be used to show which parasites are present and this helps to target product use. For example, liver fluke can be treated with flukicides that do not contain any of the wormer groups, and Haemonchus contortus (Barber’s Pole worm) can be treated with a narrow spectrum wormer. This can help minimise the unnecessary use of broad spectrum anthelmintics – and it can be cheaper too! Find out more here.
Preserve susceptible worms. What we need to try to do is to avoid exposing more worms then is necessary to the anthelmintic. This is quite easy when sheep are on heavily contaminated pasture because there is a large proportion of the worm population on the pasture and these escape exposure. At other times, there is a risk that only a small part of the worm population is outside the sheep treated, and this is highly selective for resistance. The most extreme example of this is when lambs are treated and moved straight on to a new ley, which has no worm population on it. The only worms that survive and go with the lambs will be resistant and the new ley will have a fully resistant worm population. There are two ways to mitigate this risk and make sure both resistant and susceptible worms go with sheep while still capitalising on the clean pasture. Either treat them a few days before moving (leaving them on the old pasture during that time), or leave a small number (10%) of the sheep untreated.
Review your control strategy. Are you drenching to a set pattern every year? If so, it’s time to sit down and look at the reasoning behind each treatment and whether there is scope to reduce the number of treatments or to target them better. Consult your vet or adviser and look at how you can implement these recommendations.