Ginny Dodunski, Wormwise’s Programme Manager outlines what to do when faecal egg counts indicate that worms are surviving your drench.
One of the key risk factors for accelerating drench resistance on a farm is the continued use of ineffective products.
Here at Wormwise, we’ve been hammering the messages ‘you can’t tell by looking’ (whether your drench is effective) and to ‘check your drench performance’. But then what?
What’s next if the drench testing news is a story you didn’t want to hear?
If faecal egg counts (FECs) after your routine drench show that there are still eggs in the poo samples, worms are surviving your drench.
Nowadays, the most common reason for that result is resistant worms. However, it’s still important to rule out hiccups with dosage or administration. Occasionally problems with dose calculation, gear malfunctions or administration technique can lead to animals being under-dosed, or missed.
Things to double-check are:
- Was the weight of the animals known and were they dosed to the heaviest in the group, or their individual liveweights? Or was liveweight guessed?
- Was the drench gun delivering the volume it was supposed to? Calibrating guns is an important job and should be done before every drenching episode. A medical/veterinary syringe or laboratory grade cylinder should be used to check the volume, not a jug from the hardware store. For a good tutorial on how to do this properly, check out ‘Tech tips on sheep drenching – Setting up a Drench gun’ with Wormwise trainer Andrew Dowling. Watch the video here.
- Were the people doing the drenching taking time and care to do the job properly? Speed does not win the race in the war against worms. Bob Marley is better background music than Iron Maiden!
The pattern of FEC results can be a clue as to whether the eggs left behind are from resistant worms or from animals that have missed being drenched.
In the ‘resistance’ situation, few to many low-to-moderate FECs (depending on how bad the resistance is) are common.
In the ‘missed dose’ situation, mostly zero FECs with one or two moderate-to-high FECs can be more common. If you are using composite FECs, it is not always possible to know which of these scenarios might be at play.
Another check that can help indicate whether eggs in the poo post-drenching are from resistant worms or a dosing mishap is worm species identification.
This is done at the laboratory (via larval culture or the new GIN PCR test). In sheep at least, the presence of a large range of worm types in the samples is more likely to indicate a drenching slip-up (e.g. animals being missed).
The presence of only one or two species is more likely to indicate resistance. Calves tend to have less of a species mix on board to begin with, but it’s still worth doing this check on them too.
Finally, repeating your drench performance check to a higher level of detail is a good idea. This involves dosing another group of animals and recording FECs and worm species identification both on the day of drenching (what was there at the start?) and then again 7–14 days later (what is being left behind?). Your vet can help you set this up correctly.
OK, so you’ve checked all these technical aspects, and it looks like you have resistant worms. Now what?
There are two main questions:
- Is the situation bad enough that I need to get these animals back in now and dose them with something more effective?
- What management strategies do I need now?
The answer to the immediate treatment question is ‘it depends’. It depends on how many eggs are left behind, and maybe what species the worms are. Lambs or calves on good feed, growing well and otherwise bright and healthy-looking, with just a smattering of eggs post-drench, may be left untreated until their next drench is due, for which a conversation is needed with your animal health advisor about a more appropriate choice. Remember, the longer you go on using an ineffective product, the more quickly you are building a future problem.
On the other hand, lambs or calves with moderate to high post-drench FECs, or on poor feed (why??) are likely to be better off treated immediately with a more effective product. This is both for their own health, and to cut in on the pasture contamination that they are creating with those resistant worm eggs.
The obvious question here is ‘what product should I use?’ The answer is (you guessed it!) ‘it depends’. If you’ve been using a single-active product, a combination of other unrelated actives may be a better choice. But be wary of this in lambs.
Many farms using a single-active Moxidectin in February/March (for Barbers Pole worm control but failing against other worms) and using a triple for the rest of the year, can have resistance to both types of drench. Seek advice.
If a ‘standard’ double combination product is leaking eggs, it’s not a given that a triple will be better. Sometimes that works, sometimes it doesn’t. Seek advice, preferably from someone who has plenty of experience coaching farmers through these problems.
The ‘novel’ drenches; Startect (Derquantel, sheep only) and Zolvix (Monepantel, sheep and cattle) are frequently advised. It’s REALLY important to double-check the performance of these, even if it’s your first time using them on the farm.
Occasionally, sick, dehydrated, stressed or undernourished young animals do not metabolise treatments the way healthy animals would, and this can lead to unexpected results.
Then there’s the management question: What do I do with these lambs or calves now?
‘Feed them better’ is always great advice – young animals on high intakes of high quality, highly digestible feed, will grow faster through to a weight and size where they can start to build their own immunity to worms and then require less drenching. In the case of calves, re-introducing supplement into their diet can be a good move to get them growing faster and reduce their overall worm intake.
If you have been ‘backgrounding’ young stock on poorer quality feed or lower feed allowances, stop this now!
If you have limited quality feed options, it may be better to sell – ‘get rid of them’.
This is especially true in sheep breeding systems if surplus lambs are pinching good feed from ewes that need to gain weight ahead of tupping. In this scenario, next years production is being compromised by below-par ewe condition, as well as loading up pastures with worms from lambs that will survive through winter into next season.
If you are selling young stock because of problems with drench performance, a responsible action is to administer a quarantine treatment before they leave the farm. Check out the Quarantine Drenching page on the Wormwise website.
Finally, what to do with the ground affected by young stock?
This will now be contaminated to a greater or lesser degree with drench resistant worms.
Think about how you might re-arrange grazing rotations so that adult animals or a different species can vacuum up these worms. A few weeks is better than nothing, but longer time periods are likely to be more effective. On some farms, earmarking areas for cropping and pasture renovation can be another way to clean up resistant worm ‘hot spots’.
For more information on drench resistance, and farm systems approaches to managing it, see the Wormwise Website: https://beeflambnz.com/wormwise.