Moxidectin use and performance in Scottish sheep flocks

IN May last year, Dr Jennifer McIntyre, along with Dr Roz Laing and Dr Fiona Lovatt, asked The Scottish Farmer’s readers to take part in a study investigating how Scottish shepherds used moxidectin (Cydectin and Zermex) to control worms in sheep, and the results make for some interesting reading.

“We had a great response from farms up and down the country and really appreciate the time people gave to the study,” said Jennifer.

“We found that 70% of farmers who replied to the survey, used moxidectin at least once during 2020.

“All the research data, in a completely anonymised form, in an online data repository at the university so that those interested can view the raw data, and others doing meta-analysis can re-use it in the future.”

Questions asked were as follows:

Do you follow SCOPS principles? (The guidelines which promote sustainable use and seek to prolong the life of wormers in a flock).

“A really useful product is the 2% long acting formulation (eg. Cydectin LA), but SCOPS advises not using it more than once a year – and encouragingly almost all of you that had used it, only used it once.” says Jennifer.

“However, concerningly, only two out of 53 farmers that used moxidectin in 2020 left at least 10% of sheep in a group untreated. This is worrying as it suggests that we’re not allowing susceptible worms to survive on the farm and could accelerate development of wormer resistance within a flock. Ideally, we would use some method of targeted selection to decide which animals to treat (e.g. weight gain in lambs, faecal egg counts (FECs), body condition score in ewes) and treat no more than nine out of every 10 sheep in a group.”

“Importantly, when we asked about moxidectin use, we found that one in four farmers told us about non-moxidectin wormers, and some specifically wrote that they weren’t sure which products were which. This suggests that pharmaceutical companies need to do more to make it clearer what medicines are inside a product and how the wormers should be used to meet SCOPS guidelines and slow resistance.”

Did you find evidence of moxidectin resistance?

“We know that moxidectin resistance has been present in Scotland for some time. However, we expected that on most farms moxidectin would still work well. We were particularly interested in finding out whether there was evidence of worms (particularly Teladorsagia and Haemonchus) reinfecting sheep more quickly than expected, while the product should still be working. We only tested six farms following moxidectin treatment, so not many,” says Jennifer. “However, we detected the presence of Teladorsagia on five of those farms, and Haemonchus on one of them, suggesting that some worms are either surviving treatment (‘head’ resistance) or are able to infect sheep when moxidectin should still be active (‘tail’ resistance). Nevertheless, the faecal egg count 2-3 weeks posttreatment was low or very low on all farms, so it is likely that this emerging resistance would go undetected unless farmers were specifically checking for it.”

If you want to find out more about the results from the WORMSS project you can watch a webinar featuring Dr Lovatt, Lesley Stubbings, Dr Laing and Dr McIntyre to hear more about moxidectin, worms and sheep scab (https://bit.ly/3U9PINV). Or you can read the outcomes in an open access paper in the Veterinary Record (https:// bit.ly/3eQFPEY). SCOPS guidance can be found at www.scops.org

RESULTS ARE in on the survey of how Scottish shepherds use moxidectin to treat worms