As wormer resistance continues to slide, year-by-year, from a looming threat on the horizon to a common and concerning advice call, more and more new advice surfaces from industry leaders on things that can be done to curb this trend. This advice surfaces through so many different sources now and with some farmers seeking worming advice from other vendors or effectively performing their own faecal egg counts (FECs) at home, opportunities to share these updates can be few and far between. Consider this series a little round up of tips, tricks, and developments that you may not have come across yet.

Concerning White Drenches

Many will know by now that these drenches have widespread resistance on almost all farms within most worm species. The exception (though some evidence of developing resistance is starting to emerge) is Nematodirus – which can cause severe and sudden diarrhoea and deaths. This worm mass-hatches usually in April or May, though this depends on the weather. At the first sign of diarrhoea in lambs in late spring/early summer, submit a pooled egg count sample and drench the entire group with a white drench – this is the only instance when we would recommend treating the entire group, rather than leaving some left untreated. If necessary, these may be retreated at 21 days – depending on FEC results. For those performing their own FECs, be wary of a negative result (unless a large coccidia count is observed, as the two can look very similar clinically) as lambs can become rapidly very sick even before there are many egg-laying adults on board – check again daily or discuss drenching the group anyway with your vet. NB: a count of even one Nematodirus egg on the slide at this time of year is significant and would warrant whole-group drenching. The message of this being the “first lamb drench of the season” is a little misleading as I recently realised chatting to a farmer: it is entirely possible that the age of the lambs and the timing of the mass hatch simply don’t collide and the lambs happen to pass by unscathed – if your FEC results don’t indicate that the “first worming” is necessary until, say, July, then you should use a yellow or clear drench as you would for the Summer/Autumn, as you will now be dealing with other worm species.

Concerning Yellow and Clear Drenches

These are the work horses of the worming world that we have to protect, as resistance becomes more and more widespread. These should be used through the grazing season from roughly late May onwards as necessary. Switching between these two groups, rather than relying on simply the same group year on year, is absolutely essential. These can be switched between drench applications for maximum effect, or at the bare minimum year-to-year. It is not enough to simply switch product, read the labels and make sure you are switching between a yellow (group 2) and a clear(group 3) active ingredient. You could easily be accidentally switching between two brands of product with the same active ingredient. Never drench at less than 25 day intervals (exception being white drenches for Nematodirus)unless you have good reason to believe that the wormer has been ineffective –you must allow time for at least some exposure to the worms for some immunity to develop. Never mix two wormer drenches at the same time.

Concerning Long-Acting Wormers

The only acceptable use of long-acting wormers in sheep is the injectable, long acting product containing moxidectin. This can be used either in the treatment of sheep scab or as a quarantine treatment as a precaution against asymptomatic scab carriers. The long-acting drench version of these products, however, should never be used. Aside from removing the opportunity for lambs to develop their own immunity through exposure, they also select for wormer resistance over an extended period of time, by ensuring that only the resistant adult worms survive and lay eggs onto pastures for a period of months at a time. These pastures, especially if continued over multiple seasons, will be seething with resistant worms, with little competition from susceptible ones. If the reason behind using these is time/labour issues of drenching lambs, I would strongly encourage you to perform FECs instead. This can be done, with a good dog, alone if necessary and if a low count is observed you may not need to treat them at all.