Welsh Government

Parasite Management Project - Monthly Update - August 2019

Testing the Efficacy of Wormers

This month has seen the start of the wormer efficacy tests with 3 farms having now completed this process. There are varying degrees of efficacy between the 3 farms as demonstrated in the summary table below. The percentage figures shown are the reduction in faecal egg count from the day of treatment to 7 or 14 days after treatment (interval depends on which wormer group). Results below 95% indicates a problem with the efficacy of that treatment.


Understanding the results -

Please note that the results are based on the simpler method using pooled sample pre and post treatment (as opposed to a full FECRT test) and we have to be careful in interpreting the numbers as they will have wide confidence intervals (e.g. a 50% result could be in a range from 70% down to 30%). Therefore, we often talk about these in terms of treatment efficacy rather than anthelmintic resistance. However, the treatments and set up of the tests was done under strict protocols by Techion’s technicians, so it is safe to assume that the lack of efficacy is more than likely to be down to the presence of resistant worms.


The best results were seen on Irwel’s farm with the BZ group not working fully and the evidence of the start of resistance to the yellow wormers. It is interesting to note that Irwel had already been applying some of the SCOPS principles and had been monitoring FEC for over 10 years now. It’s a good sign that following the guidance over the years has helped protect against multiple resistance development. For Glyn Davies, the extent of resistance was very disappointing, but he knew they had been relying too heavily on regular blanket treatments, this included the inadvertent worming of ewes when treating for fluke and scab.


Impact on stock performance?

Interestingly for Glyn, the crossbred lambs in the early season have performed better than normal and he sold a lot of lambs off grass. The end of spring and early summer saw long spells of dry hot weather which means poor conditions for worm development on pasture and a low parasite challenge was likely to be a significant factor in this good early performance. It is important to remember that wormer resistance will only affect performance when lambs have a worm challenge that needs sorting.

However, as the weather has changed so has the worm challenge and the group of lambs used for this test haven’t been performing well despite being wormed – which isn’t a surprise as the counts post treatment were still high, meaning they were still harbouring a fair burden. Coming into the autumn the farm would always rely on creep feed to help finish the last lambs off. This is a time of increasing worm burdens and it will be interesting to note if better worm control through use of effective wormers would result in lambs doing better off grass and less creep needed at the end of the season.

There is no doubt that using wormers that don’t work will have a significant impact on a sheep enterprises profitability. To quote Nicola Drew - “It’s scary to think how many of us farmers pay for wormers that simply don’t work”. Add in the loss in performance and labour it could be serious money lost down the drain.


What now for Nicola and Glyn?

Of these 4 wormer options, Nicola only had one which was effective, and Glyn doesn’t have any. Both will have to make strategic use of the two new 4th and 5th wormer groups (Zolvix and Startect) to ensure roundworms are controlled effectively in the future. This test only reflects the species present at the time of the test and at other times of the year the wormers may perform better if different worm species are present. This will be especially true in the early spring when only Nematodirus is present as there is very little evidence of resistance in the Nematodirus species of worms.

For both farms the regular monitoring has shown that wormers aren’t needed as often as what they have thought as well so that’s a positive. There are also other control measures they can look at implementing like making more use of cross grazing with cattle or using novel forages such as plantain and chicory to reduce pasture worm burdens. It won’t be easy, but all is not lost and by working closer with the vet and keeping monitoring we should hopefully see less compromising of lamb performance. Now that both know the situation they face, we can deal with the problem.