Cothi Vale Case Study


"The extent of resistance is worrying and shows why our previous policy needed to change. We will have to work harder now to ensure we can maintain good stock performance off grass."

Posted: Wednesday May 20, 2020

Name: Glyn Davies

Farm Name: Cothi Vale, Crugybar, Carmarthenshire

Farm Type: Lowland & Upland

Stock Numbers: 400 Ewes + 80 ewe lambs, 45 Suckler Cows and calves (sold as stores)

Land Area: 250 acres


Key Findings

  • Despite extensive resistance, lambs performed well this year.
  • 10 tests submitted from April to September.
  • Reduced ewe treatments by not worming pre-tupping.


Parasite Control History

Glyn farms in partnership with his parents and works off the farm as a contract shearer, electrician as well as doing steel fabrication work. This means a lot of the day to day on farm decisions are still made by his father. Hence the worming policy has remained a traditional one based on regular treatments, despite Glyn being aware of the need to change policy in light of SCOPS advice. Lambs are treated first at 4/5 weeks old and then every 3 to 4 weeks thereafter. Ewes are treated at least twice a year, this being 4 to 5 weeks after lambing and pre-tupping, In the last 2 years ewes also received a long acting Moxidectin, being combined with a flukicide for a mid-winter fluke treatment each winter (Cydectin TriclaMox) and some also had Cydectin LA last year as there were concerns over scab.


FEC Monitoring Results

Glyn only submitted a total of 10 samples over the course of the project and these are summarised below. Several of these were done in conjunction with Techion staff at the time of setup and a refresher session. Part of the reason was that Glyn struggled to get time to collect and process samples as he has so many other work commitments separate to the farming activities. This explains why no samples were done between the end of May and mid-August (shearing season). Glyn did start using more of the FECPAKG2 system towards the end of the project.



  • Ewe FEC’s at point of lambing and post lambing showed low to medium counts, this would be expected as they received Cydectin LA at Christmas time and the period of cover would continue into April.
  • Despite this, ewes were still wormed at the time of lamb earmarking / crutching.
  • The low result in ewes in September means the normal pre-tupping wormer wasn’t given.
  • Lambs were treated as normal during the summer so no change to the policy here.
  • Ewe lambs in September were very low and would have been wormed unless he would have tested.
  • Glyn also did one test on a group of store cattle and this helped the decision not to treat at that point as they had a medium FEC and looked well.


Wormer Efficacy

Part of the project was to determine the efficacy of the four main classes of wormers. A simple efficacy test was carried out in a controlled manner by Techion’s technicians, and based on pre and post pooled samples. Although not as accurate as the gold standard full Faecal Egg Count Reduction Test (FECRT) it provides a good indication of efficacy. The results are summarised here, a full detailed report on the wormer efficacy was provided separately (see WormerCHECK report).

The results are of great concern as it shows inefficacy to all 4 wormers that were tested. These are reported with a fairly high level of confidence due to the FEC results observed and it is most likely that the lack of efficacy is down to wormer resistance.








Although Glyn was expecting to find some level of inefficacy due to past worming policy, the extent of resistance was a surprise and very disappointing. In particular the results for both ML wormers were not expected as they had used very little ML wormers on the farm. Since Glyn had been involved with the farm over last 10 years, no ML wormers have been used on lambs to his knowledge, instead favouring the cheaper white and yellow options. Until 2 years ago no ML’s were used on ewes. However, since then the long acting Moxidectin wormer was used 3 times in 2 years on the ewes and it may be the case that this was enough to quickly multiply up resistance worms? Moxidectin resistance development would inadvertently mean presence of ivermectin resistance (but not the other way around). A small number of ewes would have been purchased over the last few years and if not quarantined correctly these could have unknowingly introduced ML resistant worms.


Stock Performance

Despite this extensive inefficacy, it is very interesting that lamb performance this year at Cothi Vale has been better than ever with most lambs sold off grass. This year there are only 70 lambs left in early October which will now have some supplementary creep to help them finish. Normally this would be between 200 and 300 lambs.

The favourable early season conditions of hot, dry weather following last year’s drought would have helped lower the worm challenge on pasture and likely contributed to this improved performance. An interesting factor about resistance is that it will only be a problem for a farm during periods of high worm burdens that need to be sorted by worming. In previous years when weather patterns may have resulted in higher worm challenges in summer months, the fact that many worms were likely to survive the regular worming could be the underlying reason why finishing lambs off grass was difficult and so many lambs carried over to the autumn and finished on creep.


Future Advice

Due to evidence of multiple anthelmintic failure, controlling parasites effectively in the future will be challenging. However, by continuing to regularly monitor FEC and following SCOPS guidelines the situation can be managed. We advise the strategic use of the two new 4th and 5th wormer groups (Zolvix and Startect) to ensure roundworms are controlled effectively in the future. However, we must be careful of these two groups and only use when necessary so we don’t develop resistance to them as it could happen very quickly. Other on farm management strategies can help such as grazing management, using alternative forages in the pasture and sheep bred for natural resistance against worms.

On the positive side the stock don’t need to be wormed as often as had been done. By monitoring the correct timing of worming can be pinpointed and there are fewer occasions than you think that you need to find an effective wormer.

It is worth retesting efficacy at different times of year and in particular on the other farm as results could be different. Due to question marks over the use of ML it is certainly worth confirming this result again.

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