How to cope with multi-anthelmintic resistance

David Cotterell, farm manager at Kingston Maurward College in Dorchester, says he was surprised to discover the farm had efficacy issues with three groups of sheep wormer.

Speaking during a recent SCOPS podcast, the farm’s vet Emily Gascoigne said a diagnosis of multi-resistance often creates panic, but it is manageable – the ultimate aim is to have a system that requires less worming of lambs.

Changes to grazing management, optimising ewe health, body condition scoring, doing forage analysis and perfecting the diet, especially protein, pre-lambing, are all helpful strategies. David also advocates working closely with your farm vet.

The Kingston Maurward College farm – which is a commercial, as well as an educational enterprise – has a flock of 400 ewes, and lambs in early March. “We’ve certainly improved our pasture management, there’s no doubt about it and it’s paid dividends this year, in a very strange year, putting those sheep out onto cleaner pasture,” David said. “[…] You can have a very targeted approach, not a blanket treatment for all animals.”

Not worming a proportion of fit and healthy animals also works very well for them – ewes with multiples or twin lambs may be wormed, but not singles. Looking at grazing and pasture contamination has been a key strategy – and ensuring lambs get the right nutrition means they can keep the few worms at bay. But every year is different, David pointed out. Droughts in the past few years have made things easier, but with the wet weather this year, they have used cleaner grazing, leaving the wetter grazing until lambs are old enough.

Strategically using the newer derivatives, Monepantel (Zolvix) and Derquantel (Startect), also has a part to play, Emily said, as does quarantining individuals coming in and mid to late season dosing to preserve resistance status. Some of the other wormers that have not quite met the 95% efficacy threshold can still have a place on farm, to avoid putting pressure on the newer derivatives, but this should be assessed on a season-by-season basis.

Dr David Bartley, a principal investigator in the Disease Control Division at Moredun Research Institute says treatment failure – when eggs are found post treatment – could be down to resistance, or it could be incorrect product choice, dosage, storage or administration. Animals should be weighed and dosed according to the largest animals, he advised.

Whilst we are starting to see a lot of resistance to multiple classes across the UK and globally, not all worm species and types are affected, and this can be managed, but it goes back to testing, he explained. Additionally, it may be that some treatments work better at certain times of year or for certain species, for example we have a lot of white drench resistance but it still has efficacy for Nematodirus battus.

Emily said her practice has been managing multiple flocks with triple resistance, but even having two classes working sub-optimally is quite common. “The reality is that where we look, we will find [resistance]. Flocks without any resistance are the hen’s teeth, the minority,” she admitted.

Testing is key when it comes to finding out if there is resistance that may be impacting productivity, and this is particularly important this year – the up/down weather patterns mean there are large variations in worm burdens across the country, independent sheep consultant Lesley Stubbings told Farmers Guide.

Emily’s top three pieces of advice for those with multi-resistance are:

• Don’t panic. There are lots of other reasons it might appear that a wormer hasn’t worked, including underdosing due to ineffective drench guns and weigh scales etc. It’s important to rule this out first
• If multi-resistance is confirmed as the cause, use a wormer you know works to tackle the issue in the short term, and use testing to build a longer-term picture
• Take a small number of lambs, e.g. 10, and do a pre- and post-treatment worm egg count.

Emily concluded by saying that knowledge is power: “Nothing is insurmountable when it comes to anthelmintics – David is testament to that, with a successful, profitable flock despite the anthelmintic challenge. You can manage it, but you have to have the knowledge, even if it’s a simple post-drench check to start on that journey.”

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