Understanding
Worming
Caroline Robinson,
Veterinary Investigation Officer
SAC Consulting: Veterinary Services
With thanks to: Hannah Orr, SAC
Consulting: Veterinary Services
Leading the way in Agriculture and Rural Research, Education and Consulting
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What are the issues?
•  Cattle, sheep and goat worms affect animals all over the UK and the
world
•  They are extremely important in limiting production efficiency
•  They cause problems and cost money before signs appear (~50% GR)
•  The damage can last!
•  They can also kill quickly
•  It is not enough to only treat when problems arise
•  But:
•  Resistance! (over 40 years)
•  This is due to over-use of worming medicines (anthelmintics)
•  So it is also not ok to use them more often just in case!
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Big performance loss before you notice
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What is anthelmintic resistance?
•  When worms develop ability to tolerate wormers (anthelmintics)
•  Like in “superbugs” – which are resistant to antibiotics
•  BUT - once developed, it can become genetic
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They don’t all do it at once.
Different “families” of worms
Can do it one by one
You won’t notice it until it is
rife
So: what can we do?
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How do we use wormers reponsibly?
•  It can be tricky – but we are here to help
•  With superbugs it is easier: antibiotics = doctors
•  With worms – can be bought in the shops
•  Step 1: Understand what wormers there are
•  Step 2:Understand how to rotate them and how to treat to avoid
resistance
•  Step 3: Understand when to time them, to avoid waste and increase
efficiency (i.e. by understand the lifecycle of worms)
•  Step 4: Start working out how you can avoid using them/use them less,
with your increased knowledge!
•  Step 5: Have healthier, fatter animals for life, increased profits, more
lambs/kids/calves per year and less expenditure on vets and drugs
(even for non-worm illnesses)
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But….I don’t think I have a problem…
•  It is tempting to think that a small flock or herd will have less problems
•  Especially if you don’t think you have seen any signs
•  But:
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Considerations for Smallholders
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Lack of ground – can’t spread them out
Rely on heavy grazing – can’t rest the ground
Small number of sources – could buy in resistance
Inexperience – difficulty spotting subtle changes
Lack of equipment – have to do evaluation by eye
Lack of information – until now!
•  Don’t have a problem?
•  Excellent
•  You need to be aware of the issues
before you have a problem!
Learn to body condition score – trends are as important as “thin” or
“not thin” – leaflets available from me
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Step 1: Understand what wormers there are
•  There are different “families” of wormers.
•  There can be several different products in each “family”
•  Rotate families not products!
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Families:
1-BZ; Benzimidazoles; “white drenches”
2-LV; Levamisole; “yellow drenches”
3-ML; Macrocyclic lactones; “clear drenches”
4-AD; Monepantel; “orange”
5-SI; Derquantel: “purple”
•  You can’t use groups 4 and 5 without veterinary advice
•  The rest you can get at the shop
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How can I tell which is which? – scops.org.uk
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Step 2: Rotate and treat to avoid resistance
•  Don’t use the same family every year as a habit
•  Change from year to year
•  Suspicions that one doesn’t work? CHECK by post-dosing poo sample
(details later)
•  Avoid over-use – check it’s needed if you can
•  EITHER: put sheep back on dirty pasture after treatment OR leave the
best-looking 10% untreated
•  Why? !
•  You can effectively “breed your own” resistant worms by giving them
beneficial living conditions
•  Dose correctly
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Do you drench correctly?
•  People tend to underdose when estimating weights by eye!
•  Ideal for resistance
•  Dose to the heaviest animal
•  Calibrate and maintain your guns regularly – use a syringe to check
them
•  Get the wormer right in (but hold them steady and don’t be rough – can
damage them) – over the back of the tongue
•  Store the drug correctly
•  Shake it well
•  Look at the shelf life after opened as well as general use by date
•  Withold food – 1-BZ and 3-ML wormers are more effective if you
withhold food for 12-24 hours before treatment
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Step 2: Rotate and treat to avoid resistance
•  What is a “clean field”? No sheep on it for the previous year
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Sheep on pasture: 90% normal worms, 10% resistant worms
A healthy sheep: say has 90 normal worms, 10 resistant worms
Dose and move to completely clean pasture
Sheep now has only ten resistant worms total – 100% resistant population
The ten worms breed, producing 100% resistant eggs
This pasture now gets 100% resistant worms in one go
•  If you leave your 10% best sheep untreated, they will poo out normal worms
and resistant worms, to “dilute” the resistant ones from the other sheep
•  It will preserve more of a balance on your pasture – mixture
•  Or, you can treat 100% of your sheep and pop them back on the old pasture
for a few days first, then move – they will have picked up some normal
worms again, to “dilute” the new pasture.
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This does not count with bought-in sheep
•  For bought-in sheep, you should use a quarantine procedure
•  This is to stop you buying in resistant worms, if you don’t already have
them!
•  For quarantine tx, 3 steps:
•  1) Treat ALL incoming sheep with two types of wormer – A 4-AD plus
moxidectin (which protects against scab if injectable) is ideal
•  (NOT GOATS – special instructions for goats)
•  2) Keep them away from your pasture for 24-48 hours if you can, to
prevent worm egg contamination
•  Turn them out to “dirty”, i.e. recently used, pasture to make sure any
eggs that survive are diluted
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Step 3: Understand when to time worming
•  This will vary from farm to farm depending on your lambing/calving and
your pasture management
•  For instance, did you know about the “periparturient rise”?
•  When ewes are about to lamb, and for weeks afterwards – sudden huge
increase in worm egg output, which covers your lambing pasture
•  Speak to your vet – it may only need one chat, plus occasional check in
•  Look at www.scops.org.uk or www.cattleparasites.org
•  DO NOT treat goats like sheep
•  They are very different, and complicated
•  I recommend David Harwood’s book,
or a goat worming talk
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Step 4: Start working out how to use them less!
•  Pasture types – aftermath, that grazed by cattle, or pasture with dry
adult sheep – less tx needed
•  Bio-active forages – plants that harbour less worms!
•  Worm egg counts – either instead of worming, or just to evaluate your
farm
•  Reduce wormings in healthy adult sheep and cattle where you can (find
out your status)
•  DO NOT reduce wormings in healthy adult goats (sorry!)
•  Try not to use combinations unless needed
•  Drench correctly – you will need them less often
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Worm egg counts/fluke egg counts
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Ten individual fresh poo samples
Ten airtight containers
Laboratory
Gather in corner then pick up, or just chase them all up and take
samples one by one
•  Checking the efficacy of your wormer? Time the sampling:
•  14 days after a 1-BZ or a 3-ML wormer
•  7 days after a 2-LV wormer
•  (21 days after fluke treatment)
•  Results within 24 hours
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The other tricks
•  Wean lambs and move to less heavily contaminated pasture (i.e.
avoiding the pasture previously used when lambs at foot)
•  Silage/hay aftermath, cattle grazing
•  Graze mature ewes in good body condition on “dirty” pasture
•  Or graze cattle on it – or mix sheep and cattle
•  Make sure health and nutrition is good – can use body condition score
to indicate drenches in mature sheep
•  Bioactive crops – chicory, birdsfoot trefoil, sainfoin
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What are the risk periods I need to know about?
•  Start thinking about your worming particularly at these times:
•  Around lambing – will you need to do something to prevent
contamination of your pasture for the year?
•  Around May –June – when the very severe worm Nematodirus rears
up to affect lambs
•  Around weaning- stressful times mean that lambs may be at risk of
coccidiosis as well as increased worm counts
•  In the autumn – fluke – we will cover fluke sometime in the future (ask
me about free talks!)
•  Do you house? Or do you outwinter? This will affect your worm or fluke
treatments.
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What is Nematodirus, and why single it out?
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Nematodirus is just one of many roundworms of the intestine
Adult sheep become immune
It is so important because of the way it lives
They can survive on pasture as eggs left over
They all hatch onto pasture at the same time
Sudden influx of horribly effective worms
All going into your lambs
Often lambs die before worm eggs can be detected, or before diarrhoea
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Be aware of pasture type
Look out for thirsty lambs, tucked up, by water trough
And scour
Always be aware of the hatch forecast ! (www.scops.org.uk)
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Nematodirus warning map! For your area
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Worming around lambing
Ewe immunity to worms reduces around lambing – start shedding eggs +++,
infecting lambs
BUT treating all ewes and turning out to clean pasture increases wormer resistance
on your farm
Blanket treatment means only a few worms left alive in your flock (resistant ones!)
– reproduce all over your land. Worming product then useless in future.
Advice from the Sustainable Control of Parasites in Sheep (SCOPS) is:
• Leave 10 to 20 per cent of ewes undrenched. Leave out the fittest, mature ewes
rearing singles (least affected by a high worm burden). They will regain their natural
immunity once the lambs are weaned.
• Always give correct dose – don’t under dose.
• Drench ewes at or very soon after lambing. Do not leave till later, and don’t drench
twice unless discussed with your vet as suitable for your particular wormer product/
management/risk
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SCOPS recommendations
Weigh largest sheep and use this dose for whole group. If wide range in weights, split into
smaller groups and dose to heaviest in each of these.
Do not use this rule of thumb with combination fluke-wormer or flukicide products – some of
these can be toxic at a slightly higher dose, particularly in pregnant or stressed sheep.
Check drenching gun is working properly by discharging it into measuring syringe/jug. Make
sure the sheep are well restrained and nozzle goes over the back of the tongue.
Research has shown white (BZ) and clear wormers (ML) work better on an empty stomach withhold food for 12 to 24 hours before treatment. When drenching heavily pregnant ewes, it
may be better to use a yellow drench (LV).
If all sheep have been drenched, return to original field to pick up a few susceptible worms
before moving to clean pasture.
Know your anthelmintics and how to rotate them
Know that there are options that can help you avoid unneccessary use!
Know how to body condition score to spot trends before there are obvious signs
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Resources to help you out
•  www.scops.org.uk
•  www.nadis.org.uk
•  www.cattleparasites.org.uk
•  Your vet – do you find yourself on forums asking veterinary questions?
Why? Underuse of available resource?
•  Leaflets and publications – SCOPS, COWS or on the SRUC desk at
festivals or conferences
•  Me – I do free requests! (not singing)
•  Worming is one of the two most important things you can get right to get
healthy, happy, productive and efficient animals
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It can all be quite convenient too!
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Any questions? (Or do we need some coffee?!)
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