Drench resistant worms in sheep – current myths & half truths

Sheep, farming, husbandry, health, worms, internal parasites, current practices, myths, half truths.

By Dr Clive Dalton

Myths & half truths won't clean up these backsides!
Dagging has been an accepted part of sheep farming since
the start of farming, but we can't afford the time, cost & physical pain
of dagging sheep any more.

Because of the way internal parasites operate in sheep, and the methods we have used in the past to control them, a lot of myths and half truths have become interwoven with good solid facts.

Myths are defined as ‘traditional narrative embodying popular ideas’ so some bits are true or half true, but others are certainly not. Myths are things we want to be true!

Examples:

1. The more you drench, the quicker you’ll have worm-free stock.

Not true. You will never create worm-free stock and you would not want to either. Sheep need worms to challenge their immunity. But the more you drench the greater the chance of multiplying resistant worms.

2 You cannot farm without drench.

Not true. Some farmers are already doing this. They had no choice as they have already ‘hit the wall’ and used up all their drench options.

3. Drenching stock will eliminate worms from pastures.

It won’t. It will reduce larval numbers but to what extent will depend on a long list of factors.

4. If you don’t graze pastures for 3-6 weeks, all or most of the worm larvae will have died.

Not true. We now know that larvae can remain viable for up to 6 months, never mind 6 weeks.

5. Drenching hoggets at monthly intervals from weaning through autumn and winter with 5 to 7 drenches will make doubly-sure that they are worm-free as two-tooths.

Not true. Hoggets and two-tooths still produce worms long after the drenching stops.

6. If one drenching interval is not working, then shortening it will.

Not true. Drenching more often can easily build up drench resistance as resistant worms have a reproductive advantage.

7. Using long-acting drenches in sheep will delay the onset of drench resistance in worms.

Not true. Good evidence is building up that this will hasten the development of drench resistance.

8. Drenching ewes, especially with long-acting drenches, at pre-lambing and docking will prevent them infecting their lambs.

Not true. This will build up drench resistance in the flock even faster because the resistant larvae passed out by the ewes and recycled by the lambs will have a reproductive advantage.

9. Tapeworms have serious effects on the health of lambs.

Not true. Masses of research prove that tapeworms are not a serious problem. They look much worse than they really are.

10. Newly-drenched lambs should be immediately put on to clean pasture or special lamb blocks.

Not true. The chances are very high that the clean pastures will be contaminated with drench-resistant worms as all the susceptible worms will have been killed by the drench. They should be held for at least 4-5 days (some vets say 2 weeks) on old contaminated pasture before shifting them on to the lamb block.

11. Breeding is far too slow a way to fix the worm problem.

Not true. If you use an accurate way to identify worm resistance in both males and females and select flat out for this trait, you’ll be surprised at how fast things can change

12. New worm resistant genes, and developing new drenches and vaccines are just around the corner.

Pigs will fly! The current generation of farmers with average age 50+ should not hold their breath.

Disclaimer This material is provided in good faith for information purposes only, and the author does not accept any liability to any person for actions taken as a result of the information or advice (or the use of such information or advice) provided in these pages.

Drench resistant worms in sheep – a worm's life

Sheep, farming, husbandry, worms, internal parasites, health, definitions, genus & species, life cycles, signs of wormy sheep, effects of worms on sheep

By Dr Clive Dalton

What are ‘worms’?
‘Worms’ is a general term used for internal parasites that affect sheep. Plenty of other terms are used such as:

• Roundworms (the main species that are round in cross section)
• Nematodes (a general name for roundworms)
• Cestodes (a general name for tapeworms)
• Helminths (includes round worms, flukes and tape worms.
• Internal parasites (live inside the animal which is their host).
• Gastrointestinal worms (inhabit the sheep’s four stomachs and intestines
  

Worms in New Zealand

• Apparently twenty nine species of internal parasites got a free ride to New Zealand with livestock but the most important ones in sheep ended up being the round worms - Haemonchus, Ostertagia, Trichostrongylus and Nematodirus.
• All the roundworms are found throughout New Zealand but their relative abundance varies between districts, and with the age of the sheep and time of year.
• Only sheep and goats share the same species of worms. Some sheep and goat worms may survive going through other species, e.g. cattle, but they are not viable after their journey.
• All worms are classified by the Latin name of their genus and species. A few have common names but some of these are as ugly as the Latin names so they are not in common use.
• The table below gives some examples. Within each genus there are many species only some of which cause problems. The subject can be complex when discussing any problems they cause. Often the genus is only used to describe the species adding to the confusion.
  

• The abomasum is the 4th stomach where final gastric digestion takes place. In the previous three stomachs (rumen, reticulum and omasum) fermentation by bacteria and micro-organisms takes place.
  
• When using the species name the first letter of the genus is used to save writing it out in full.
• Key point: In the past, farmers didn’t need to worry about these names but things have changed, so use this table as a quick reference when talking to your vet or consultant. Hopefully you won’t ever have to write them down!
  

Can you see them?

Barber's Pole (Haemonchus) can be seen by eye once concentrated in a jar

• You can’t see round worms with the naked eye when mixed in among stomach and gut contents.
• Once the gut contents have been washed through a fine sieve and the worms collected and suspended in alcohol, then you can see them en masse. Some are so fine you can only see them when the specimen jar is shaken.
  
• Haemonchus are easy to see in a specimen jar.
• Tape worms sections are easy to see when passed out in the dung. These regularly panic farmers into drenching lambs.
• Tapeworms are a very minor issue in stock health and plenty of research shows they can be ignored.
  
• However, some farmers believe they are associated with other health problems in lambs such as pulpy kidney, flystrike and trace element deficiencies and so drench lambs as a protection.
  

The sections of tape worms are easy to see in faeces

Worm life cycles
Round worms:

• Both sexes of the mature worms live inside the sheep (the host) where they mate and produce eggs.
  
• These then pass out on to the pasture in the dung which protects them, and where they feed off bacteria.
• The eggs hatch inside the faeces and start to develop into larvae. They go from the L1 to L2 stages, and then to the L3 stage which is the critical one, as it’s eaten by another sheep to start the cycle all over again.
• The ecology of these larvae is not fully understood, but it’s known that L3 larvae can spend a long time in the ground. They can go 10-20cm down and move back to the surface when sufficient moisture is present. They are aquatic creatures.
• Warm moist conditions encourage the L3 larvae to migrate up plant leaves in a film of moisture to be eaten by the new host.
• Larvae need a minimum of 2-6 weeks of warm moist conditions to develop successfully.
• It takes about 21 days for ingested larvae to develop into adults capable of laying eggs.
• When developed, larvae survive longest in moist and cool (even frosty) conditions. Larval peaks occur in autumn (the autumn rise), with a more variable peak in spring (the spring rise).
• Some larvae can live for 6-8 months in cooler temperatures (sometimes even longer) and in warmer conditions they will die after 2-3 months.
  
• These facts have come as a shock to most of us who were taught that a 3-6 weeks grazing rotation would kill most of them. It won’t.
• Key point: In New Zealand, 85-95% of the worm population is found as larvae on pasture, so only a small proportion is inside the animal at any one time.
  
• Lambs are the real culprits by ingesting larvae and putting out large numbers of eggs, and this continues through to the hogget and early two-tooth stage.
  
• Worms love lambs and the earlier they can infect them the better.
  

Liver flukes:

• After ingestion the fluke larvae bore their way through the liver tissue causing damage which then affects liver function.
• Mature flukes are hermaphrodites (having both male and female sex organs) and live in the bile ducts from where their eggs pass out.
  
• These eggs need to go through a fresh water snail to hatch into larvae which are eaten by the sheep again.
  

Lungworms:

• They reach maturity in the lungs where they mate and lay eggs.
• These hatch and L1 larvae move up in the mucus and are swallowed to pass out in faeces.
• On the pasture they moult until the L3 infective stage and are eaten by the sheep off the pastures to complete the cycle.
  

Tapeworms:

• Their heads attach by hooks to the small intestine wall, and with no mouth they absorb nutrients through their skin. The egg-rich (gravid) rectangular sections pass out in the faeces where the eggs after hatching (either inside or outside the sheep) are eaten by a pasture mite.
• After 15-30 weeks they develop into larvae and are eaten again by a sheep. Lambs are most prone to tapeworms but seem to self-cure themselves by 8 months of age.
• A large evacuation of tape worm sections in the faeces of lambs is certainly impressive. It’s easy to panic when seeing them, assuming they block the gut so must have a terrible effect on lamb growth.
• The experience of some farmers shows that the very distinctive smell of lambs with tapeworms and their scour attracts blowfly and drenching avoids all this extra work.
  

What do worms feed on?

• Roundworms live off the proteins in the mucus lining the gut wall.
• Lungworms feed off similar mucus in the lungs.
• Blood suckers (Haemonchus only) attach themselves to the gut wall with savage-looking mouth parts and feed on blood.
  

What do worms do?
They cause a range of problems, either singly or in combinations. Here’s a selection:

• Key point. Partial or complete loss of appetite.
• Damage to the gut lining causing inflammation.
• Interference with the production and absorption of digestive juices.
• Leakage of fluid from the gut and an increase in mucus production.
• Dehydration through scouring.
• Blood loss from the gut wall (Haemonchus only).
  

Have worms any benefits?

• All animals have worms so it’s important that their immune systems can respond to deal with them.
  
• So they actually need a worm burden to stimulate the very complex immune system to respond to the challenge.
  
• This takes time, and when a worm burden swamps the immune system problems will arise.

What are the signs of ‘wormy’ sheep?
There are plenty of signs and you may see some or all of the following:

• General unthrift and looking tucked up and lethargic.
• They are easy to catch as they generally fall over!
• They can show a massive weight loss.
• Pot belly and low body condition. They are very skinny and their backbones will be visible from a distance despite their wool covering.
• Diarrhoea (scouring) instead of well-formed faecal pellets or ‘marbles’.
• Mucus in the faeces. Note this does not always mean worms.
• Anaemia. The mucous membranes of the eyes and gums are very pale. There is no skin pigment anywhere.
• White rectangular sections in the faeces (tapeworms).
• A ‘bottle jaw’ – skin pouch hanging down from lower jaw (liver fluke).
• Lack of ‘bloom’ in the wool. Wool with good bloom has high grease content.
  

In the past, when you saw scouring (diarrhoea), you automatically suspected worms and grabbed the drench gun. Not any more! There are many reasons for scouring, so get a veterinary diagnosis before drenching.

Disclaimer This material is provided in good faith for information purposes only, and the author does not accept any liability to any person for actions taken as a result of the information or advice (or the use of such information or advice) provided in these pages.

Drench resistant worms in sheep – the situation on your farm

Sheep, farming, husbandry, disease, animal health, worms, internal parasites,


By Dr Clive Dalton

Answer this question – it’s compulsory!
Are the worms in your sheep resistant to the chemicals in drenches currently being used?

1. If ‘YES’, then get your veterinarian or consultant to work out a strategy to continue farming your sheep sustainably.
2. If ‘NO’, then make sure your conclusion is right, and is based on sound information and not just imagination or hope! Your future business could be based on a myth.
3. If the answer is ‘DON’T KNOW’, then talk to your veterinarian or consultant urgently to find out what’s going on and develop a strategy for the future.
   

Key point 1:

• Read the Rattray report (see further reading) and check that anyone giving you advice has studied it too. It's available free from NZ Meat & Wool.
  
• It was done in 2003 and covers 228 pages but is still essential reference and discussion material for when you talk to your professional advisers to plan a sustainable sheep enterprise.
  
• All New Zealand’s experts have made valuable comments in it and it covers world research.

Key point 2:

Fill in this form to assess where you are at, and which will help you have a very profitable conversation with your veterinarian. Click on the image and it will expand in a new window, suitable for printing.

Think - Premium lamb

• Think about the increasing pressure coming from export markets about food safety and the international demand for chemical-free produce.
• Talk to anyone in a meat company who has had to do a ‘trace back’ under terrible pressure from an overseas customer breathing down their neck, threatening to cancel a major shipment. They say it’s a nightmare.
• Imagine how delighted meat companies will be in future to be able to source lamb which is ‘chemical free’!
• Stock that have had minimal or no drench are already starting to demand a premium. Think about meat ‘lambs’ (hoggets) being sold before June that in normal circumstances will have had seven drenches by then if not more.
  
• How much more would they be worth if they had received no chemical drench?
• It won’t be long before farmers buying store lambs and meat buyers sourcing lambs for export will be demanding details of the drench status of the stock.
  
• The ASD forms will become even more valuable documents in future.
• Store sheep buyers will soon demand information on whether the sheep have been drenched, when they were drenched and what product was used to prevent importing problems of drench resistance, and having to worry about quarantine drenching.
• Ram breeders producing worm-resistant rams to breed progeny that can be farmed without chemicals will certainly earn a premium.
  

Which of these sale rams will produce progeny that can be farmed without chemicals?

Disclaimer This material is provided in good faith for information purposes only, and the author does not accept any liability to any person for actions taken as a result of the information or advice (or the use of such information or advice) provided in these pages.

Drench resistance worms in sheep –farm management options

Sheep, farming, husbandry, animal health, worms, internal parasites, management options


By Dr Clive Dalton

Happy sheep & happy worms
Sheep have been farmed intensively for centuries in Britain before some of them were brought to New Zealand. Every ancient shepherd knew that ‘a sheep’s worst enemy was another sheep’, and the only way around this was to appreciate the concept of having ‘happy sheep and happy worms’.

The so-called advancement of agricultural science with its chemicals and the drive for more production changed all this – and now we are finding it was not all progress after all.
If we go back to the old principles of ‘sheep husbandry’, things are certainly a lot more involved than just pouring drench down a sheep’s throat.

In the ‘old days’ before modern anthelmintics, farmers had to spread their risks through management. Here are some of the things that used to be called ‘integrated management’ but now you read about a ‘management tool box’. It sounds good anyway.

Option 1. Feed stock well

• This seems so obvious! A sheep in good body condition is healthy and it will have a good digestive system and an effective immune system, which will then look after most things. The sheep takes care of its own health.
• Always maintain a good pasture cover, and don’t make sheep graze down hard leaving low residuals so they will end up eating a lot of worm larvae.
  

Option 2. Use FEC to find areas of low larval contamination

• Here you use FEC on a regular basis to monitor worm output from your different groups and classes of stock – remembering that the FEC tells you what was going on in the sheep three weeks ago.
• To use this technique it would be best to have your own gear to keep costs down, and you’d need a good grazing diary to record what was where on the farm and for how long.
• You will then know which areas have had the highest contamination of eggs and then larvae.
  

You then have these options:

• Keep all sheep off that area until the larvae have been reduced naturally by time and desiccation.
• Graze the area with another species – e.g. cattle (you’ll need plenty of them).
• Graze the area with ewes that have high immunity.
• Avoid grazing with young lambs that you want to grow well.
• If you have to graze the contaminated area –use an appropriate drench at the correct time. This approach will reduce the total amount of drench used.
  

Option 3. Keep stress levels down

• This was always part of old-fashioned ‘good shepherding’, especially in lambs after weaning in the heat of summer and up through the early hogget stage.
  
• This makes a lot of sense knowing that this is when the lamb/hogget is developing its natural immunity.

Things to avoid
So here are some common sense things to avoid if possible. You see them all the time on farms where shepherds and dogs are overworked and tired.

• Bringing large mobs of lambs/hoggets into yards and holding them for long periods to do other jobs with them.
• Not providing water or shade in holding paddocks.
• Packing lambs too tightly in pens at sale yards for all day in the sun with no water.
• Doing many jobs at the one time to minimise work –e.g. weaning, drenching, shearing and dipping.
• Causing long truck journeys without rest, feed or water.
• Having crazy dogs that most times are out of control.
• Not droving any sheep (especially newly-weaned lambs) to near exhaustion on bikes!
  

Option 4. Graze pastures with mixed species of animals

• An example would be a 60-day cycle starting with lambs for 7-10 days, ewes for 28 days and cattle for the balance.
• The problem of using cattle as vacuum cleaners for sheep larvae is that you will need a lot of them – something well over 50% cattle to sheep ratio, and you may not want to farm cattle to this extent, especially if they are not making a good return on their investment and they cause more work.
• This is regularly glossed over in discussions and nobody seems to produce figures on how many cattle you need, or the costs and returns of this advice.
  

Option 5. Grow crops

• There’s a very wide array of crops to choose from and plenty of good advice from agronomists. The promotional literature would convince you that every crop and its many cultivars is a guaranteed winner.
• Before growing a crop work out the economics. Weeds and low yields are regular causes of financial disaster.
• Remember also to cost the time the paddock is out of grazing waiting for the crop to grow. This all seems common sense but the pictures in the glossy catalogues seem to swamp a lot of this.
• Many sheep farmers are not great cropping farmers – at least not in the North Island where the worm problems are generally worse than in the South Island.
• Crops such as Lotus or chicory are known to reduce the worm burden and achieve high growth rates in young stock. But again, they are not easy to grow and keep weed free, and may not last as long as the brochures say under your management.
• Do the sums first!
  

Option 6. Pasture renewal

• If you believe some agronomists this should be a regular part of all farm management programmes. Some recommend renewing 10-20% a year!
• Go back and ask why the pasture has to be renewed and what ruined it in the first place? It might be cheaper to fix that.
• If it’s being renewed just to get worm-free grazing for lambs, then make sure you do the sums first about how much profit you’ll end up with.
• In any case it’s not an option on many hill country farms.
  

Option 7. Hay and silage regrowth

• The regrowth on silage and hay paddocks should be larvae-free so is ideal for growing/finishing lambs.
• But on most sheep farms, not much conservation can be done and certainly not on hill country farms. So again this may be a limited option.
• Feeding stock well and keeping stress down look like the best options. Whatever you decide, make sure your do a full budget before choosing an option from the magic management ‘tool box’.

Conclusion:
If you are realistic, the above points are all limited options on most hill country farms, so do the best you can.

Disclaimer This material is provided in good faith for information purposes only, and the author does not accept any liability to any person for actions taken as a result of the information or advice (or the use of such information or advice) provided in these pages.

Drench resistant worms in sheep – drenching to control worms

Sheep, farming, husbandry, animal health, worms, internal parasites, drenches, anthelmintics.

By Dr Clive Dalton

Well, which one are you going to buy? Will the store assistant know enough to help you?
Beware of being told that 'this one's a good seller at the moment'! Or this one has the free jerkin'.

Drenches on the market
It is mind boggling to see the enormous range of products (anthelmintics) on the market to treat internal parasites in sheep.

Anthelmintics are any products that kill internal parasites, and past annual surveys in farming press show the following:

• There were around 40 different brands on the market.
• These were made by 5 companies.
• 15 were sold by vets only, and 16 were available from all outlets.
• Concentration of the chemicals ranged from 1g/Litre to 40g/Litre.
• Ingredient dose rate ranged from 0.2mg/kg LW to 10mg/kg LW.
• Formulated dose rate ranged from 1ml/5kg LW to 1ml/20kg LW.
• Withholding periods for meat ranged from 3 to 91 days.
• Safety margins ranged from 3x the dose to 100x.
• 15 of the products were ovicidal (killed worm eggs) and 16 did not.
• All of them killed both mature and immature parasites.
• 17 products included minerals, 1 had vitamins and 2 included vaccines
  

Ways to deliver

• Products can be given as an oral drench, as an oral bolus or capsule that stays in the rumen, or they can be injected.
• Check the label about the injection method (it’s usually subcutaneous) and for the best site (in the neck).
• There are no straight pouron ‘anthelmintics’ for sheep.
• Other products are called ‘endectocides’ as they kill both internal and external parasites and can be administered by mouth or injection in sheep. Pouron endectocides are not used in sheep.
• Some products are ‘ovicidal’ which means they also kill worm eggs in the sheep, as well as the worms.
• When checking the survey table of drench brands on the market, remember the ‘active ingredient’ column is much more important than the brand.
• And when you buy, don’t let the promotional ‘giveaways’ bias your decision.
  

Key questions:

• Is it any wonder that we get confused when buying drench? Have sympathy for the shop assistant too having to give advice and make recommendations when customers have no knowledge of the subject.
  
• Is it any wonder the customer buys a product with the lowest price and the best promotional give-away?

The drench chemical families

• Only a few years ago we didn’t need to know much about the chemicals used in drenches, but things have now changed.
• The key issue is that all the different products on the market are based on only three chemical ‘action families’ or ‘actives’. Active ingredients have long names that are hard to remember.
• We’ve got to get over this as it’s now very important to be able to ‘talk chemicals’ to your veterinarian or consultant.
• Calling them ‘white’ and ‘clear’ drench families was once helpful, but now not all white drenches are white and not all clear drenches are clear!
• Labeling does not always tell you clearly which family the product belongs to. You have to know your chemicals to find this out with far too many products.
• The printing on the labels is very small to fit in all that legally has to be presented. So it’s hard to read and no company has provided a small cheap lens to help the ‘average’ farmer who at over 50 years old needs some visual assistance!
• Current knowledge is that each chemical family kills worms the same way – thank goodness for that! So if a worm is not killed by one type of white drench then it won’t be killed by any other chemical in the white drench family.
• The unfortunate result of all this is that farmers now need to be more aware of the active ingredients in the specific brands of drench within each chemical family.
• This is now especially important when buying a branded product. You’ll have to recognise which chemical family the drench belongs to and know what species of worms it is expected to kill.
• Use the Table below as a check list to show which active ingredient is in which chemical drench family. You’ll need to check this when buying branded products. The table doesn’t list the chemicals used in double- or triple-combination products – so check the label. Don’t buy the product if you are not sure what’s in it and you cannot find out.
  

Key point:
Once your sheep have drench resistance to some or all three families of actives, flock management and your life will be a lot more complicated.


How anthelmintics work

• After drenching, the active ingredient is absorbed from the gut and circulates through the blood stream throughout the body, and is then resecreted back into the gut to do its work.
• Some active ingredients can also kill worms through direct contact with the parasite in the gut.
• When blood levels of the chemical drop below an ‘active’ level, then the drench loses its power.
• The length of activity of a drench depends on a range of factors related to the formulation and the worm species in the host.
• ‘Persistence’ is the term used to describe how long after administration a chemical in the drench will still work. For example the chemical in control-release capsules lasts a long time so is very persistent.
  

The gut trigger

• This is a clever bit of engineering in ruminants called the ‘oesophageal groove’.
• It is nature’s way of making sure milk when swallowed by the young lamb goes straight into the 4th stomach or abomasum for gastric digestion where it can clot.
• You don’t want milk going into the other three fore-stomachs (rumen, reticulum and omasum) where bacteria and other micro-organisms are developing to digest fibre.
• In the adult animal certain minerals and chemicals can close the groove so the drench will bypass the rumen where you want it to go.
• Large volume drenches are more likely to trigger the groove than low-volume drenches – so low volume products are a feature you should also look for and check with your veterinarian.
  

Disclaimer This material is provided in good faith for information purposes only, and the author does not accept any liability to any person for actions taken as a result of the information or advice (or the use of such information or advice) provided in these pages.

Drench resistant worms in sheep – a farm with drench resistance

Sheep, farming, husbandry, disease, animal health, drench resistance, dealing with problem

By Dr Clive Dalton

What do you do to find out if your sheep have worms resistant to drench?

Acknowledgements
Thanks to Dr John Moffat, Schering-Plough Coopers for use of this case material.

The problem

• A family farming operation on a North Island hill country farm running 1200 ewes and 150 beef cows was concerned about the effectiveness of their sheep drenching programme, and suspected that maybe drench resistance had developed.
• This was because of poor growth rate, scouring and an unacceptably high death rate in their lambs (100 died between docking and weaning). They normally had to dag about a half of their ewes.
• Their suspicions were really alerted by a mean FEC of 800epg 10 days after drenching a mob of hoggets with ‘Closal’. Closal is a narrow-spectrum active which has roundworm-persistent activity against Haemonchus contortus but is also highly effective against liver fluke.
• No worms have shown drench resistance to it yet in New Zealand.
• Lambs were on a standard 7-drench programme of which two were given prior to weaning (10th September and 20th October), a weaning drench on 20th November followed by four drenches on 20th December, mid February, mid March and mid April.
  

Action taken

• The first step was to arrange for a ‘drench test’ to see what was happening, so 60 hoggets were used to carry out a Faecal Egg Count Reduction test (FECRT) starting in May 2004. The results are shown in the table.
• The percent reduction in pre and post-drench faecal egg counts overall and by different parasite species was revealed.
  

Key points from the table:

• Note the wide range in individual animal’s FEC within the groups. This is expected.
• A drench is considered effective if the egg count is reduced by 95% or more.
• So the Lev, BZ, Combo drenches were not effective. Indeed the egg count was higher in the post-drench than the pre-drench FEC for the BZ group. This can happen.
• The MLs were 100% effective.
• Culturing larvae is an essential part of the FECRT to see which species are killed by which drench family.

• Look for the 100% kill rates and clearly the Lev drench was killing three species, the BZ killing one and the Combo was still killing three species of worms.
• Trichostrongylus parasites were resistant to both BZ and Lev drench, and so have had a reproductive advantage on this farm.
• Not enough parasites had developed resistance to ML to be detected as yet, i.e. ML drench was still killing all species cultured.
  

Drenching Recommendations

1. Develop and monitor the farm drenching programme

• Review carefully the current programme.
• Future drench usage must be warranted based on sound knowledge.
• Monitoring of parasitism in the flock is needed to ensure the on-going control programme is working.
• Do another FECRT in autumn to check for Haemonchus resistance, in case it is a threat when a narrow spectrum active should be used,
  

2. Drench active options are limited.

• Never use single action BZ or Lev drenches or Combination BZ or Lev drenches.
• Never use BZ capsules.
  

3. Protect the efficacy of ML family:

• Use other long-acting drenches very sparingly.
• In general minimise ewe treatments.
• Do not use long-acting drenches in ewes.
• Use preferably combination ML drenches or ML products on their own.
• Combination examples should contain ML+Lev or ML+BZ+Lev.
• Don’t drench about 5% of the animals in the mob (the best ones).
• Drench to the heaviest animal in the mob and regularly check the drench gun.
• Check FEC routinely before and after drenching using a composite sample.
  

4. Maintain Border Security

• Ensure there is no spread of drench resistant parasites onto your property from other farms or from your farm to others.
• Quarantine drenching.
  

5. Other Recommendations:

• Reduce farm parasite burden.
• Make use of cattle in cross-grazing programmes.
• Carefully consider post-weaning lamb management.
• Ensure good nutrition.
  

Disclaimer This material is provided in good faith for information purposes only, and the author does not accept any liability to any person for actions taken as a result of the information or advice (or the use of such information or advice) provided in these pages.

Drench resistant worms in sheep- immunity

Sheep, farming, husbandry, disease, animal health, worms, internal parasites, immunity, what helps & depresses immunity

By Dr Clive Dalton

What is immunity?

• The body can chemically recognise things which are either 'self' (which is accepts), or 'non-self' or foreign (which it rejects). It then tries to destroy the invaders with antibodies produced from white blood cells in organs like the spleen and lymph nodes.
• Antibodies produced by a first invader challenge may not be as high as that from a second challenge (a booster), which results in much more antibody being produced.
  
• This is the principle behind vaccination against disease. One vaccination is followed later by a booster.
  
• Animals to develop immunity to internal parasites just as they do to bacterial and virus infections, and they use this as a defence mechanism. At one time that’s all we needed to know.
• But now we need to understand more about how immunity works which is not easy, as the ‘immune system’ is not located in a single organ. It’s described as being one of the most ‘proliferative organs of the body', meaning that it operates in many different cells so clearly must be complex.
• There is 'passive' immunity made up of pre-formed antibodies, which an offspring gets from it's dam via colostrum, and then there's 'active' immunity produced from antibodies the animal develops itself.
  
• Developing active immunity takes about 10 days after a challenge, but can last for the rest of the animal' lifetime.
  
• Immunity to parasites develops more slowly than to bacteria and there is a nutritional cost involved.
• Part of the immune response to internal parasites is to shut down the female worms’ ability to produce eggs before it gets rid of them from the gut.
• Immunity increases with age, remembering that a worm challenge is good, but a massive worm burden will swamp the animal’s immunity until full immunity is established.
• In sheep, immunity is normally fully developed in their second year of life but an ideal is to have them with at least around 50-60% immunity by 6-8 months of age.
  

What helps immunity?

• The ideal situation (best practice) would be to let a sheep’s immune system develop without the need for anthelmintics. Unfortunately in practice, farmers are forced into drenching to control the worms.
• To maintain good immunity, animals need periodic or continual challenge by the parasites – so sheep must have some worms in the system for a continuous (but manageable) challenge.
• But an immune response can get too high which has a cost in nutrients and will most likely reduce the other performance traits of the animal. So SIL breeders are encouraged to use the Dual Purpose Overall (DPO) Index which incorporates disease resistance Breeding Values (e.g. WormFec or Facial Eczema) to balance up these genetic conflicts.
• Protein is very important to immunity. Damage to the gut by worms causes protein leakage, and the immune response which occurs in the gut uses lots of protein. This loss then means there are less nutrients available for the rest of the body – especially the valuable carcass.
• Deprived of protein, the animal cannot then mount an effective immune response to worms so better feeding, especially increased protein at this time is important. Feeding clover-dominant pasture is the best option to do this.
• The late Mrs Gladys Reid, OBE, pointed out research in humans and animals showing that zinc, selenium and vitamin B12 are important to develop and maintain a healthy immune system. She also pointed out that zinc and selenium are lost from the gut when enteric infections and upsets like scouring occur.
  

What harms immunity

• The young lamb before and immediately after weaning is most vulnerable. It needs to develop immunity as soon as possible at a time when there is a high demand for nutrients for growth. But at the same time it can be full of parasites and pouring out worm eggs. So it’s very easy for these things to get out of phase and internal parasites take a great toll.
• Research has shown that anthelmintic drenching of young lambs pre-weaning can delay the advancement of their own inherent genetic immunity. This is an enormously important finding in the drive to identify worm-resistant sheep – but has not been widely broadcast.
• Bloodsucking lice in young lambs (infected from their mothers) can cause anaemia and this will also reduce the build up of immunity. Check with your vet for an appropriate treatment and timing.
  

The periparturient rise

• Immunity levels drop in ewes for about 4 weeks around lambing so worm populations can increase rapidly. This is called the ‘periparturient rise’ or PPR.
• Also around lambing and early lactation, ewes like dairy cows are in ‘negative nutritional balance’ when their energy output cannot be met by feed intake – so they are under added stress.
• The periparturient rise is higher in twin-bearing ewes than in those having singles, and it’s higher in two-tooths than older ewes.
• If the animal’s immune system is stressed by other factors such as hunger, poor feeding, bad weather, low body condition, or carrying and feeding multiple lambs, then the worm burden will have a greater impact on the immune system and animal performance, so the periparturient rise will be greater.
• Despite recognising that mature stock have the highest immunity against internal parasites, farmers still claim benefits from drenching ewes.
  
• The general view now is that this should be avoided unless there is an established parasitism problem, especially in young ewes in poor condition where feed is short and hence animal welfare may be compromised.

Genetic improvement of immunity

• There is great individual variation between animals in their inherent level of immunity, and at the age this occurs. This is especially important when we start looking at selection opportunities to improve a trait like host resistance.
• Research and farmer experience has shown that fortunately immunity can be genetically improved. Two lines of AgResearch sheep were selected for over 20 years for ‘resistance to worms’ and ‘susceptibility to worms’.
• By 8 months of age the resistant line had developed 80% immunity to parasite burdens, while the susceptible line were only 20% immune. A ‘normal’ line used as a control showed 50% immunity by 8 months.
• But the dilemma was that the high immune sheep were less productive. This is a common finding in other farm animals such as beef cattle and pigs and is always disappointing to farmers.
• An important finding from breeding research is that ewes selected for low FEC as lambs retain their status around lambing, and are not hit as hard by the periparturient rise and record much lower FEC than susceptible ewes.
• Key point: Anthelmintics have a major negative effect on the developing immune system in the lamb. So to really help a lamb develop its immunity to worms, the less drench it gets the better.
  

Do anthelmintics harm the immune system?
This very important question was never asked in the past; we took it for granted that if drenches killed worms, then all the news had to be good. The concern today is that this question is still not being asked enough. Sheep farming was all about 'killing things' and after drenching with the latest product, everyone involved in the job felt better!

Thinking has changed in some quarters, although the research showing the bad effects of anthelmintics is still not widely publicised, especially in veterinary circles where they have to sell drench. Here are some important points to ponder.

• When a lamb's delicate immune system is developing, some very complex things are going on at the cellular level. The authorities on the subject will tell you that little of this is understood at present.
• We know that animals vary greatly in how they handle this process.
  
• Some handle it with ease in a very short time (e.g. 6 months), while in others it can take twice as long and also inflict a considerable nutritional cost. Such sheep will need extra care and a greater protein intake – all adding to costs.
• So getting a lamb to develop its natural immunity early is a money saver as a lamb, and also in its later life, when it won’t need as much drench (if any). Beyond 9-10 months of age, little if any immunity develops.
• So it makes sense to keep anthelmintics out of lambs. They should be used to help vulnerable animals during the critical 2-3 months after weaning, and at other times when you think a massive worm load may impair production and welfare. Consult your vet about this.
• At all costs, avoid the old schedule of monthly drenching by the calendar, when lambs after weaning and through winter used to get 7 drenches or more. The more drench they got the more their immune system was damaged - and the more money was wasted.
• Some advisers now recommend that products containing albendazole should not be given to ewes in early pregnancy as it may damage the developing embryo. That tells you something about the drugs used in drenches!
  

The store attendant will assure you that all these products are good, because that's what the company rep told them. And remember 'the special offers' to consider.
And why do they put products in bright coloured packs?

Disclaimer This material is provided in good faith for information purposes only, and the author does not accept any liability to any person for actions taken as a result of the information or advice (or the use of such information or advice) provided in these pages.

Drench resistant worms in sheep – other options

Sheep, farming, husbandry, disease, animal health, worms, internal parasites, options to avoid drench, organics, homeopathy, minerals, evaluating products, future developments

By Dr Clive Dalton

When none of these products work any more
- what options do you have?

When drenches fail - what happens
When the day arrives when you find out that the current range of anthelmintics will no longer work on the farm, you will have to sit down and ask where you go from here. The chances are that the consultants and vets you have been using will be as worried as you are.

At present there are the following options:

1. Use 'survival of the fittest'

• This is survival with a vengeance when you lock the drench gun away. What will happen is unpredictable, as it depends on how big a worm and drench resistance problem you have.
• Expect poor stock health and performance for some years, but this again will be hard to predict.
• The biggest worry is how lower fertility and poor growth of young stock will affect the number and quality of flock replacements. You may be forced to buy some in of unknown drench resistance status.
• Your bank manager may not like this idea, as they hate surprises and unpredictable events.
• A few farmers have done this because they ran out of drenching options. They say it was very hard in the first couple of years, stopping drenching, ruthlessly culling all daggy sheep and having to breed their own rams. But then things came right fairly quickly after that and they’ve never looked back.
  

2. Go organic sheep farming

• Initially this always sounds a great idea when you hear about the premiums for organic meat. But before getting carried away – ask organic sheep farmers about internal parasites and how they manage them as they are a major problem.
• If officially registered as ‘organic’, (which requires an annual fee) farmers can use their own preparations usually based on cider vinegar, seaweed and the plant wormwood.
• Organic sheep farmers are allowed to use homeopathy.
• Plants containing condensed tannins such as plantains are claimed to bring about some control as are the leaves from poplars and willows. Drenching with cold tea has also been used – again for its tannins.
• When in the opinion of a veterinarian the health and welfare of animals are at risk, then conventional remedies can be used, and indeed they must be used under current law to prevent pain or suffering. All animals treated then lose their organic status and can only regain it after a specified period in quarantine on the farm.
  

3. Use homeopathy

• Traditional scientists are highly sceptical and openly critical of homeopathy, because they say it lacks scientific evidence showing statistically significant benefits.
• Homeopaths say there has been documented research done – but the disagreements between the two sides go on and it looks like a very long war.
• While this is going on, an increasing number of veterinarians now offer both conventional and homeopathic remedies because they believe many current methods of preventing animal sickness (not improving health as homeopaths point out) with chemicals including anthelmintics are not sustainable.
• Homeopathy is based on the ancient principle of ‘using like to treat like’ and hence improve the general wellbeing and immune system of the animal so it can control its own health.
• Homeopathic products need not be registered as ‘animal remedies’ under the Agricultural Compounds and Veterinary Medicines (ACVM) Act 1997 as long as the provider does not ‘make a claim’ as to what the product will specifically cure or prevent.
• Makers can describe products as ‘promoting general health’ but that’s about all. Users of products can make claims about benefits – but not the manufacturer.
• There are severe penalties for anyone selling an ‘unlicensed animal remedy’ and a major reason for this is the threat it could be to food safety and our overseas markets.
• Farmers can either accept what they read and hear about homeopathic products, or do some simple comparisons on their own farm to see if there are benefits.
  

4. Use mineral & trace element products

• There is plenty of old peer-reviewed research to show that minerals (especially copper, selenium and zinc) help growth and the development of a young animal’s immune system.
• Hence there are a number of products on the market, given orally as a drench, or fed as a meal or lick to exploit this.
  
• They are sold to promote ‘the general health of sheep‘ and that’s about all the manufacturer can say about them, as they are not registered as ‘animal remedies’ under the NZ Agricultural Compounds & Veterinary Medicines (ACVM) Act 1997.
• If a product is not registered (showing an ACVM number on the pack), then the manufacture breaks the law if they “make a claim” that the product will do something or the other like kill worms.
  
• The makers can only make general statements saying their product assists overall health and boosts natural immunity, but that’s all. It’s similar situation with homeopathic products. The user can make claims as to benefits on their farm, but the manufacturer cannot do this.
• The products contain minerals and trace elements- and there‘s plenty to choose from. Some include vitamins making the brew even more complex, and farmers assume that if it has all those goodies in it – it’s got to be good. If it smells good (e.g. Cider vinegar) this seems to be attractive.
• Some farmers add their own extra brews, and there is no law against this if it’s used on their own livestock. It’s not a wise practice and could cause animal health problems and human food safety issues.
• The big justifiable complaint of farmers is that manufacturers of these products are loath to hand out literature with details of trial results, and they won’t tell you what’s in their brews.
• There are two reasons for this. First, the makers could not afford to get their products tested by an official research organisation, and secondly, if they said what was it their product, somebody would copy it as they cannot afford the high cost of patents, which are easy to get around in any case.
• When questioning the use of these products (which is always a good idea), remember that farmers will try new things but if they don’t work they don’t re-order, and may not even pay the bill. So for an honest assessment, check with people who have used anything new for some time (at least 12-18 months) and paid their bills.
• Key Point: If products truly help to enhance immunity, then that’s all good news. If they allow you to reduce or cut out anthelmintics – then that’s an added bonus, which also helps immunity. So then it will be much easier to identify highly immune sheep to improve the accuracy of selection.
  

Evaluating products on your farm
In these days where so much independent research done by old government departments of agriculutre has been killed off, you have to be very careful accepting research results done by commercial companies who also sell the product they are testing! So it’s tempting for farmers to test thing on their own farm.

This is not easy and all that is ever achievable are very basic comparisons, provided you pay attention to some important points:

• Realise that anyone with a formal scientific training will rarely accept your results. If you find major benefits – somebody will always say that it was a fluke and that you probably even ‘cooked the books’! Ignore them as the objective is to convince yourself.
• You must have an untreated ‘control’ group that are similar in age, sex, weight and background to the treated group or groups. Indeed the control group is the most important one!
• Aim for at least 25 animals per group – the more the better as animals disappear on farms!
• Manage all the groups in a similar way – and run them together if possible.
• If you need to run a group separately (e.g. to avoid cross contamination), then ensure they have similar grazing and management.
• Before you start – discard from the total group any animals that look sick or are very large or very small. You need to get your trial sheep from an even line to start with.
• Then randomise them into their trial groups. Simply draft them off in turn through the race for each treatment group.
• Look them over after drafting to check there are no ‘odd-ball’ animals in any group. Discard these and replace them with animals picked at random again from the main mob.
• Make sure all sheep are well identified by groups – a good long-lasting raddle mark may suffice. Individual ID using tags is nice but it may not be necessary.
• Make sure their ID will last till long after the trial has finished as you’ll be amazed at how interesting these sheep may become later. And in any case you may not see benefits for a long time.
• Data recorded could be things like live weight and FEC/FCS at the start and end of the comparison. Don’t get bogged down recording too much – only essentials that you need to make a decision. Keep it simple.
• Record the information in a hard-backed exercise book and not on separate sheets of paper that will get lost. Don’t worry about the book getting covered in sheep muck – it’s a working document!
• If you don’t get at least a 10% difference between any treated groups and the control – be wary of drawing any conclusions. Assume there are no differences – which is a very important conclusion indeed! This will certainly save you money from buying things that don’t work.
• Be wary of seeing things through rose-tinted spectacles as the mind can play tricks and confirm what you want to happen. Remember this is what a myth is.
• If you want to assess visual differences between groups – then get someone from outside who has never seen the sheep before to do the job and don’t tell them which group is which.
• Remember – the aim is to avoid fooling yourself by spending money on products that don’t work.
  

Promised future developments
There are certainly plenty of things talked about and being researched, but it depends how long you are prepared to wait. When you hear researchers interviewed and read reports of their predicted delivery times – it seems we only have to wait for 2-5 years and at most a decade.

But because of the stop-start way research is funded these days and the bureaucratic and commercial restrictions on getting results out to farmers at a sensible cost, don’t hold your breath! The average sheep farmer at age 50+ will probably never see most of these.

But with a positive outlook - here’s the current wish list:

• New drench chemicals.
• Biological anthelmintics that interfere with normal worm metabolism.
• A pasture L3 larvae test to locate high contamination areas to avoid when planning grazing.
• Plants with condensed tannins such as Lotus or plantains.
• Vaccines to enhance the animal’s own immunity. This is the Holy Grail of parasite control!
• Fungi that kill worm larvae on pasture or in the soil.
• Genetic markers (called Marker Assisted Selection of MSA) using DNA profiling to find sheep resistant to worms.
  

Disclaimer This material is provided in good faith for information purposes only, and the author does not accept any liability to any person for actions taken as a result of the information or advice (or the use of such information or advice) provided in these pages.

Drench resistant worms in sheep - dealing to dags

Sheep, farming, husbandry, disease, animal health, worms, internal parasites, dagging, solutions

By Dr Clive Dalton


What everybody knows

• Dagging is the worst job on the farm- hated by everyone but accepted as part of the job.
• If dagging was clearly listed in a shepherd’s job description, applicants would be scared away. Imagine “bonus for dagging” being featured? Yeah Right!
• Dagging is a pain in the back, hips, knees and brain! These afflictions can only get worse with the average age of a sheep farmer being 55+ years. ACC statistics have always shown that 40% of sheep farmers have bad backs and have learned to live with the pain.
• Shearers won’t dag sheep, as it’s a health and safety issue. They can also refuse to shear daggy sheep, as they are about as popular as damp sheep.
• Dags are sheep dung, and salmonella and campylobacter love them.
• The wool industry doesn’t want dags. ‘Average quality’ dry dags (with some wool yield) make around 20c/kg but low-quality dags are worthless. Wool brokers don’t trade in dung.
• If you can get someone to dag sheep, the current cost is up to 70c/sheep. In the next few years – if there are any volunteers for the job left it could easily be $1/sheep.
• Sheep are getting heavier and these costs will apply even if sheep handling devices are used rather than dragging sheep across the board.
• The cost of dagging to the nation must be astronomical! I’d guess half a billion dollars if you added all things in like wasted time and medical costs for an aging farmer population. You could charge hip replacements at around $15,000 each and knees at $14,000 each. You may get a 15% discount for a pair!
• So to solve the sheep industry’s problems, it’s no good waiting for increased returns. Farmers will have to cut costs with a vengeance and getting rid of dagging must be top of the hit list to produce low-cost sheep.
  

The old solution

There's no shortage of drench in attractive containers with
bright colours, supported by sales
promotions from free jerkins to golf clubs and iPods

• Drench and more drench was the answer. Nothing was more simple! The farm staff felt they’d done a great job and killed all the worms – especially if the yards were full of tapeworms. The dogs got a good run and it was a good chance to school up young huntaways with frequent filling and emptying the crush pens.
• And at least after drenching (if the product worked) the sheep dried up for a while to give you some respite from growing more dags. If it didn’t and sheep slowly started to scour again, then you drenched them again in a few weeks.
• It was wonderful when the long-acting anthelmintics devices came along that stayed in the rumen and drip-fed anthelmintics. This was until worms started to develop drench resistance.
• Sadly these old solutions are still used today by farmers who need to do some fresh thinking while drenching.
  

What needs thinking about now?

• Dags are soft faeces that stick to wool and even to bare skin. So breeding bare-bummed and woolless sheep is not the solution. It will help, but there are far too many other issues with these sheep to complicate this approach.
• The standard approach has been: worms = scouring = dags. Drench was seen as the way to fix all three but this approach needs to change.
• Sheep don’t get up during the night to go to the loo - they lie where they are and let it flow! So if dung is soft, they’ll lie in it before morning and rise with soiled wool and more dung stuck to existing dags. So dags can multiply rapidly from the inside and the outside once they start.
• ‘Marbles’ and ‘hand grenades’ (with low moisture content) don’t stick to wool – even if a sheep lies on them. Check sheep night-camp areas in a morning and see the little mountains of marbles. They are works of art! Then notice the great squashed heaps of plops or slops with the impressions of wool in them from overlaying.
• Having a decent tail dock helps the muscles around the anus to eject faeces. Sheep (with tails) wag them when defaecating to help ejection and the two ligaments under the tail control this. So don’t dock tails off by the body and follow the Sheep Code of Welfare. Some stud ram photos in adverts currently show the very worst examples.
• Notice how people who promote and sell drench to prevent dags don’t dag sheep for their clients. The last dagging they probably did would have been when they were young and fit, and only for a short time such as on work experience. It would be nice if a drum of drench came with a voucher for a week’s free dagging by the supplier along with own food and drink.
• Key Point: If you mate rams and ewes this season that are genetically dag producers, then add 5 more years of dagging their progeny on to your current age! It would pay to buy the bigger drench pack that comes with an iPod to load with your favourite music to help relieve the pain when dagging on your own in the years to come. It’s worth a thought.
  

The solution – genetics

• It’s interesting that more farmers and veterinarians are remarking that some sheep in a flock, regardless of the feed (sloppy or dry), need regular dagging and others don’t.
  
• This is old news, but not much was ever done about it –other than drench the whole flock again, which was always the easy option.
• If they’d looked closer they’d have seen that the ‘non-daggers’ produced marbles or hand grenades and didn’t poo their pants like the sloppy ‘daggers’ did.
• There are enough farmers around now who can prove that culling persistently-daggy sheep will reduce the number of bales of dags in the shed and all the wasted time involved.
  
• Some say it took a long time, and others say it was surprisingly quick once they became driven to fix the problem by health or labour problems.
• Good research has shown that dags are inherited. The average of a few heritability estimates is around 25% which is not high like fleece weight, growth or FE resistance (around 35-40%), but it’s good enough to make some positive change if you crank up the selection pressure (Selection Differential) on both the male and female side. Note the word ‘both’.
• So try this for logic. If ‘dags’ on the outside of a sheep are inherited, then what produces them on the inside, (measured by FCS) must be inherited too.
• Remember the advantages of marbles. They are produced by healthy sheep, don’t stick to the wool and they kill larvae fast on the paddock.
• So the genetic solution is simple – mate ‘marbling’ rams to ‘marbling’ ewes and you’ll be on fast track to breeding dag-free and worm resistant sheep in the one go. It’s scary that the job could be that simple.
• It’s certainly worth thinking about and giving it a go. It’s not going to cost you any more and if it works, then life will be very much easier for both shepherd and sheep.
  

What to do

First step - drafting into clean and dirty mobs

• Keep the job simple and cheap - so avoid consultants!
• Check the faecal consistency score (FCS) of all rams to be used as well as their FEC. Remember that they should not have been drenched for at least two months (preferably more) before testing to get a decent estimate of their genetics.
• FEC on it’s own is not good enough any more as you could easily end up with low-FEC dag-producers from soft faeces (plops, slops and scour). FEC and FCS must go together.
• If you are worried about the accuracy of a single FEC/FCS, do a couple more a week or so apart to check repeatability.
• Make sure the samples have been done at a reliable lab that has checked their accuracy. You need to ask for a High Dilution method to make sure no eggs are missed to get an accurate value for selection purposes.
  
• You are not wanting to find out if the results justify giving the animals a drench, so it’s very important to explain what you are doing to your veterinarian.
• There’s evidence now coming through from stud flocks using FEC/FCS to check their two-tooth and older rams, that they maintain their ranking among their peers, and they don’t seem to show the big worm-egg spring rise seen in ewes. This is good news.
• So if you take repeated samples for FEC/FCS at different times on rams or ewes, and they differ by only a few hundred epg, then that’s quite acceptable. But if they vary by thousands of epg, then there‘s something funny going on and it would be wise not to select that animal.
• If you have already joined the rams with the ewes, then wait till the rams have finished mating, and check their FEC/FCS after a month’s rest.
  
• It’s the range in values that’s important, and it will either delight you (if it’s low), or make you very determined to get serious next season if it’s high.
  
• You could easily have spread ‘dag-producing’ genes through the flock for the next five years and beyond.
• Zero FEC with FCS 1 of marbles is the Holy Grail. If you have any of these rams, they are ‘non-dagging’ gold nuggets, and you cannot waste their genes by random mating them to any old ewes in the flock.
• Get the faecal probe out (contact me for details) or use your finger and find some ewes with marbles or if there are not enough accept hand grenades as a mating group.
• Then do a FEC on them to check they are zero or under 500epg. Your CFA old girls would be ideal to find these to form a nucleus of ‘no-dag’ sheep to increase their gene frequency in the flock. This trait must be given top priority in your selection.
• This will get you going to deal with dags, and give you time to think about the next stage. Go back and check out the breeding chapter again.

Disclaimer This material is provided in good faith for information purposes only, and the author does not accept any liability to any person for actions taken as a result of the information or advice (or the use of such information or advice) provided in these pages.

Drench resistant worms in sheep - breeding worm-resistant sheep

Sheep, farming, husbandry, disease, animal health, worms, internal parasites, breeding, breeding for resistance
By Dr Clive Dalton

Breeding - the only solution

Question: How come in the same flock, some sheep
are always clean and others always dirty?

Increasing numbers of farmers are starting to accept that breeding sheep, that are genetically resistant to internal parasites is the only way towards a sustainable future.

The precedent was set 30 years ago, when a pioneering group of breeders started to select sheep resistant to Facial Eczema (FE). It’s been enormously successful, and shows that if you have a clear aim, and you can keep the programme simple, it will bring results.

• Whatever are the rights or wrongs of past drenching practices, we have got to make an aggressive start to breed sheep resistant to worms. For some, this is now an urgent priority.
• It’s sobering to think that over the last 100 years in New Zealand when trouble arose, there was always a quick escape to grab what was needed through outcrossing to a new breed.
• For example we used Finnsheep to fix low fertility, different breeds provided scope to change wool types, and different meat breeds were used to meet market changes. New Zealand’s sheep history right up to the present shows how sheep importations and outcrosses were used as quick-fixes to change genetics.
• But when drench resistance really takes hold, where do we go? There is no readily-available outside genepool that is going to work this time. Countries like Australia, United Kingdom and South Africa have serious drench resistance too so it’s no good rushing there for solutions. They could be heading here for help.
  

Commercial sheep farmers have two clear options.

1. They can either buy in the genetics they need from the current industry’s stud breeders who have been selecting for host resistance, or
2. If these sheep are not available, they will have to breed their own. Those farmers with severe FE were forced to breed their own.
   

There’s no time to wait
Farmers in tough times cannot wait around for slow changes to take place in the stud industry. Predictions are that some farmers may only have 2-5 years left before most drenches will fail on their properties.

These implications are massive for the stud industry, and could cause as big a revolution in sheep breeding as Group Breeding Schemes did in the 1960s and 1970s. We could be heading for interesting times again with the ghosts of many old scientists rising from their graves to join in!

Genetic improvement works

• Enough work has been done already by AgResearch and a few top breeders to confirm that breeding host-resistant sheep works, while recognising that it takes a long time to get there - around 20 years to reduce FEC by 50%.
• Hopefully, genetic technology will speed this up in future (depending on cost which is never mentioned).
• If you delay making a decision and do nothing, expect problems, as remember resilience is weakly inherited (5-15%), whereas drench resistance in the worms has reasonably high heritability (23-25%).
• So if you do nothing the parasites will become drench resistant faster than you can improve resilience. But much more work needs to be done on the genetics of these traits as heritability estimates can jump around a lot and are not set in concrete.
• Clearly the aim is to improve host resistance to worms and not just resilience, but initially both of these will be happening at the same time and you won’t know how much of each.
• Don’t worry, as FEC/FCS will help identify animals that have developed host resistance in the long term.
  

Challenge to the stud industry

Stud breeders annual sale - how many can
offer you guaranteed dag-free and worm resistant genes?

• It would be nice if commercial farmers could simply ring up a SIL breeder and order all the rams they need to fix any approaching drench resistance crisis. (SIL stands for Sheep Improvement Ltd).
• Well they can’t, because at present not enough SIL breeders have rams available that have been tested. You can’t blame the SIL breeders as they have not been asked for them and demand creates supply.
• A big change is needed and fast but don’t hold your breath.
• So commercial farmers in trouble need to give serious consideration to starting a simple flock improvement programme including keeping their own rams.
  

A programme to think about

• I’ve set out below a breeding plan. You’ll have to decide if it’s an option for your farm and if you are prepared to accept the challenge!
• Don’t go into it half-heartedly as you’ll end up with a shambles and there will be plenty to say “I told you so”. It needs your full commitment.
• Key point: If you are a commercial farmer with a decent-sized flock and cannot buy the rams you want that are dag free and with proven host resistance to worms, then you cannot afford to wait around for stud breeders to respond to your needs. Get started!
  

Getting started

• It might be a good idea to take a few deep breaths before reading on –as there’s a fair chance you may get lost on the way through.
• Go through it slowly with your own flock in mind, and remember what the aims are in each part. Maybe don’t read all the parts in one go?
• Remember the overall aim – to breed sheep with a high natural (genetic) immunity to internal parasites. Keep remembering this if you get lost in the detail and lose track of what’s going on.
  

Two clear challenges

• The following breeding programme will bring results in commercial flocks of around 1000 – 1500 ewes.
• It probably would not be worth starting with fewer than 500 ewes because of the intense selection needed.
• But you may like to try it with a small flock and see how you get on. The challenge is twofold:

1. To keep the job simple and above all avoid getting bogged down in paper records.
2. To keep costs down to a bare minimum.
   

Genetic theory
The genetic theory behind the breeding plan is notnew. It was used by Thomas Bakewell in the 1700s to improve English Longhorn cattle and Leicester sheep, so it has been tested!
As students we were sick of hearing about him.

His painting showed a little fat man wearing a black hat, with a pigtail and fancy jacket sitting on a little fat pony.

I bet he never dreamed we’d still be using his simple principle of ‘breeding the best to the best’. The job is to sort out what is the best. So let’s start.

Four pathways
There are four ‘genetic pathways’ to flock improvement. Below is not the way these paths are usually listed, but this order is for a sheep flock starting at scanning in mid pregnancy. Here they are:

• PATHWAY 1: Selecting females to breed females
• PATHWAY 2: Selecting females to breed males
• PATHWAY 3: Selecting males to breed females
• PATHWAY 4: Selecting males to breed males
  

So start in mid pregnancy, but if this is not convenient, don’t worry – just dive in where you can. The key point is – make a start somewhere!

PATHWAY 1: Selecting females to breed females

Ewes in mid pregnancy

• Start by scanning the flock to identify (ID) the twin-bearers. Run them separately and feed them well.
• Do NOT drench any ewes in the flock from now on. Avoid any long-acting drenches like the plague!
• Lamb these twin-scanners separately and give them any extra care you can afford at lambing.
• Cull any that ‘pack up’ between scanning and lambing, that grow dags, or have any lambing or health problems. Be ruthless and if in doubt – throw it out!
• If you are ‘easy-care’ lambing – then don’t go near them.
• This is the start of the journey, as out of these twin-scanned ewes you’ll be continually selecting the very best for commercial traits that keep you in business.
  

At docking

• Do NOT drench any lambs on the farm at docking – and this means in the entire flock unless you have an animal welfare crisis.
• Do NOT drench any ewes on the farm at docking either.
• The twin-scanned ewes. Dock their lambs separately and mark all the ewe lambs (Use ear-markers to cut a bit out of the ear or punch a hole).
• Mark any twin-scanners for culling that are wet/dry or have any other problems that you don’t like. Be ruthless!
• If the twin-scanners go back with the main flock (or in case of escapes), identify them with a temporary mark that will last till weaning, or better still, give them a permanent ID with a small cheap plastic tag.
• This cost of this small tag (and not a big one) is justified at this stage and then your past work is protected.
  

At weaning

• Plan to keep many more ewe lamb replacements than normal, as you are going to put intense ‘selection pressure’ on them (i.e. cull heavily).
• As a target, plan to cull around 30% of these lambs – but this will depend on the final numbers you’ll need.
• Do not drench any ewe lambs wanted for replacements.
• The ewe lambs from the twin-scanners will have been earmarked at docking, and will be the core of your future replacements.
• Hopefully you’ll get all the replacements needed from the twin-scanners and will not need to go too deeply into the non-twin-scanners to make up numbers. But this will depend on twinning rate and the season.
• Any lambs for sale from the remainder of the flock can be drenched with a conventional combination drench if they look wormy, and if you think it will improve their sale prospects. If the bidding stalls at the sale tell the auctioneer that they’re ‘newly-drenched and they’ll shift well’!
• Before sale and after conventional drenching, run these sale lambs separately from the replacement ewe lambs. You don’t want any cross-contamination between worms.
• If you see tapeworms in any lambs, ignore them and do not drench unless you are sure they are doing harm. Use a drench specific to tapes.
  
• Be especially vigilant to mark for culling any ewes and lambs anywhere in the flock that have any physical defects.
• At this stage the lambs are starting to develop their natural immunity so there will be great variation in the number of daggy backsides you’ll see. Some may go through a daggy stage and then permanently dry up.
• So make your final decision in the autumn when they are hoggets (see below) and they have had more time to show early immune development.
• Pay special attention to the twin-scanned ewes at weaning and their replacement ewe lambs. Cull any that fail to meet your standards. Be ruthless, especially on dirty backsides.
• f you didn’t tag the twin-scanned ewes at docking, then make sure you give them a good permanent ID now. You cannot afford to lose them now as they are going to be the core of an ‘elite’ flock (see Pathway 2).
  

Ewe Hoggets

• When these weaned ewe lambs are hoggets, go through them every 2-3 weeks (a month is too long) and draft off the ‘tail-enders’ that have not measured up for culling.
• Pay special attention to those that have been frequently daggy and get rid of them.
• If you think they need it, give the tail-enders a conventional combination drench and finish them for sale. Again tell the auctioneer the good news about them having just been drenched!
• Before sale and after drenching, don’t mix them with the replacement ewe hoggets. The drench status will have to go on the ASD form if they are within the withholding period for the product.
  

Take a moment
Now take a moment and evaluate how far you have come from weaning, and guard against the urge to conventionally drench the hoggets. What the hoggets look like will be a early sign of any progress made towards resilience and/or host resistance.

• Satisfy your curiosity and boost your faith in the exercise so far, by doing a FEC from each of 10 different (fresh) heaps of dropping in the paddock. Remember to correct these for FCS.
• Discuss the results with your veterinarian provided that they are up with the play on recent developments, and that drench sales are not the main priority.
• Use a trigger level of 500 epg to see how things are going, and conclude that fewer than 500 is resistant and above 500 could be anything, resistant or resilient or a bit of both. You don’t want them.
• But remember to look at the animals in light of these trigger levels.
• Be strong and guard against the urge to drench these hoggets by the calendar or because the dogs need a run!
• Mid winter (May-June) is an ideal time to start putting even more selection pressure on these replacement hoggets. Cull heavily any that fail to meet your standards – and especially any with dirty backsides.
• Buy, borrow or share some scales and weigh the hoggets to decide a cut-off (cull) weight in the light of how many you need to go into the flock. Find the range by weighing a few of the smallest and a few of the biggest, and then decide a cut-off ‘target’ weight.
• Keep on being ruthless and cull any hoggets that are even slightly daggy, lame, or have any other physical defects you don’t want in the flock. Be ruthless.
• It would be a great idea to go through the hoggets with the faecal probe and identify those with FCS of 1 (marbles) and 2 (hand grenades) – or mark for culling any with clearly soft faeces (3,4 and 5) to get rid of any with genes for dags.
• Keep the drench gun locked away unless there is a worm blow-up (e.g. Barber’s pole) and animal welfare is compromised.
• After all the work you’ve put in so far, it’s time to put a reliable permanent tag in them showing individual number and year born. They are now your most valuable animals – and you had better believe it!
  

Hogget shearing

• In the past it would have been worthwhile weighing the wool and keeping those ewe hoggets with high fleece weights – but don’t bother unless you can do it easily and you think it will give an objective measure to reduce numbers further.
• Hoggets with high liveweight will also have the genes for high fleece weight (the genetic and phenotypic correlations between the two traits are highly positive).
• If wool was worth more in overall returns, then things may be different. However, if you breed fine wool then it would certainly be worth culling on hogget fleece weight.

Two-tooth ewes

• These ewe hoggets have now become two-tooths and should look a picture because remember their background and the intense selection pressure you have put on them so far.
• Also remember that so far, their individual FEC is not known. Apart from the odd sample to monitor progress, it’s not worth doing any more FEC. It doesn’t matter at this stage whether they are resilient or resistant or a bit of both.
• Keep on being ruthless and culling any that develop problems like footrot.
• If you want a confidence booster, do another FEC on 10 of them, just to see how their host resistance is building up.
• The next job is to plan their mating, so you’ll have to decide what kind of rams to buy and where are you going to get them from?
• These top two-tooths certainly deserve something special that can improve their genetics for host resistance to worms, and not just to get them pregnant. There are two things you can do:
  

Option 1.
You may already have a ram team on the farm purchased from SIL or other stud breeders in the past. Check their FEC/FCS making sure they have been drench-free for at least 2 months (preferably 3).

Option 2.
Check what rams are available for the current season from breeders using SIL.

1. Using your current ram team

• Your current ram team bought from SIL or other stud breeders in previous seasons will have been a considerable investment, and it would be well worthwhile to see what their worm resistance status is by doing a FEC on all of them. Make sure they have not been drenched for at least 2 months (preferably 3) before the FEC.
• Rank them on FEC/FCS and decide what trigger levels you can afford to accept. Whatever the FEC, don’t use any ram that has ever had a dirty backside or not thrived over winter.
• Aim for nil FEC or certainly not higher than 500 epg and with FCS of marbles or hand grenades.
• If you have high-Index rams that you paid a lot of money for, and they have higher-than-acceptable FEC, test them again before considering their future as culls.
• This exercise will be a very good investment as you could be either shocked to see what possible genetic worm resistance you had bought in, or you could be pleasantly surprised.
• It’s going to be vital information for when you talk to your ram breeder for next year, either to order more or cancel the lot! At least you have valuable factual information for your decision which may bring about some industry change. Pigs may fly before this!
• If you want to buy more rams from the stud breeder next season, then demand to see FEC/FCS from the rams on offer – making sure they were not drenched for at least 2 months before the test or never drenched at all. The response could be interesting!
  

2. Buying in rams from SIL breeders

• Contact your nearest consultant from Sheep Improvement Ltd (SIL) by phoning 0800-745-435, or Email .
• Find out which breeders are formally selecting for host resistance to worms and incorporating it with other productive traits into an overall Index.
• Make sure the breeders are doing this formally though SIL which will show in an official logo (WormFEC™) on their Ram Selection List.
• But be prepared for snags. Despite the SIL WormFEC protocol in the Breeders’ Manual (1994), some breeders have developed a few variations of their own, so for example, check how many of their total rams on the selection list are included in WormFEC data to go into their DPO index. Others may be using the SIL dag score too to add into the overall DPO index.
• The FCS is not accepted by SIL information. So for your own protection, it would be a good idea when you have your potential purchases sorted out to check them with the faecal probe for marbles or hand grenades, and avoid like the plague any with soft faeces (FCS or 3, 4 or 5).
• Note they should not have been drenched for at least two months before sampling – which may be an unrealistic request from a client.
• Because of the low numbers of ram suppliers doing this at present, expect to pay a premium for their rams.
• Make sure you use these rams to their maximum and certainly much more than accepted mating ratios.
  
• See blog on how to get the most from a Worm Resistant (WR) ram.
  

PATHWAY 2: Selecting females to breed males

• Your main task now is to search for dams of future rams (ram mothers), as these are going to be critical. They need a special status so call them your ‘elite’ ewes. They will be thrilled about this!
• You won’t have to look far to find them, as the ewes that started off as twin-scanners and have been ruthlessly culled right through to weaning their lambs, have got to be the core of the elite flock.
• Your ram supplier or agent won’t like this idea, especially when you say you have closed your flock and want to severely reduce or cancel your ram order for next season.
• You had better make sure you have some sound genetic and economic reasons to support your actions. Tell them what you are doing and especially why, and invite them to come and see your elite ewes. Use their reaction –positive or negative as motivation.
  

The elite flock

• Aim to end up with from 7-10% of your total ewe flock in an elite group. Be flexible though.
• Keep going back into these elite ewes and (depending on numbers needed) keep culling them hard for any physical defects and health problems (especially any that are daggy, had flystrike, are lame or have simply packed up). Keep searching for structurally sound robust ewes.
• Continue to be ruthless, and if you have any doubts about a sheep, cull it.
• YOU need to have great confidence in these sheep, as they’ll be great motivators for you and your staff as the programme proceeds.
• Expect to get cold feet from time to time over what you are doing – and you’ll doubtless have criticism from some quarters. Use any criticism as motivation to succeed.
• In your doubting moments, just go and walk through the elite ewes and see if you can fault them or if you have seen any better ones on the way home from town! This will restore your faith in the exercise.
• If you know of any skeptics, invite them out to the back of the farm to see the elite ewes as that’s where they’ll be. They won’t be grazing the hay paddocks by the road!
• If you need more ewes to boost elite flock numbers, select them from two-tooths that scanned twins, i.e. if you marked them and kept them separate. If not remember to do it next time.
• These elite twin-scanned two-tooths need to be screened for FEC. It will be worth spending money on taking individual samples and keeping the best sheep with low FEC corrected for FCS (below 500 epg).
• This would also ID any that had very high FEC for future culling.
• If you can’t afford the FECs, then at least use the faecal probe to cull any that don’t have a score of 1 (marbles) or 2 (hand grenades). If you have the numbers, only go for those with clearly-defined marbles.
  

Maintaining the elite flock
This is a vitally important part of the exercise. To maintain the elite flock, use the same simple rules that you used at the start of the programme.

To gain entry into the elite flock in the first place, or to regain entry at any subsequent lambing, then a sheep must have completed all of the following:

• Scanned twins.
• Not been wet/dry at docking.
• Survived all the culling on constitution, health and structural soundness – and not caused any extra work or cost you money!
• Have shown some clear evidence of being host-resistant to worms through good performance and low FEC.
• Never shown any sign of a dirty rear end and have consistently produced marbles or hand grenades.
  

Docking ram lambs from elite ewes

• Keep all the ram lambs entire from these elite ewes.
• Do NOT drench any of them.
• Permanently ID the ram lambs at docking by taking a bit out of the ear or punching a hole.
• Or put a small plastic tag in them if you have enough helpers.
  

Weaning ram lambs from elite ewes

• Do NOT drench any of these ram lambs at weaning.
• Treat them as for the ewe lambs (above).
  

Ram hoggets

• When these ram lambs are hoggets, manage them the same as for the ewe hoggets, except put a lot more selection pressure on them. A good starting target is to cull 80% and end up with 20% for the final selection.
• Every 2-3 weeks (a month is too long) after weaning, draft off any ‘tail-enders’ and if you think they need it, give them (the culls) a conventional combination drench and mark them for sale.
• They’ll make good money during the winter and remember the auctioneer will proudly tell buyers they’ve just been drenched and will shift well!
• OR before drenching - advertise them as ‘chemical-free’ lambs or see if your meat company is interested in them at a premium.
• Don’t mix the drenched culls with those kept as replacements.
• Be very strict on what you keep, and get rid of any that don’t meet your standards.
• In mid winter, do the same as for the ewe hoggets, weigh them and cull the tail-end on a target weight.
• Now give them a permanent ID (number and year born) with a reliable plastic tag if you didn’t do it at docking. They are very valuable stock.
• Keep culling any animals that fade and get daggy. Look for those animals consistently passing marbles and hand grenades. Be ruthless!
• Record their live weight twice. First in May (winter) and then in August (spring).
• As there will not be large numbers at this stage, it would be worthwhile recording fleece weight at hogget shearing (usually in October). Cull those with the lowest fleece weight and off-type wool.
• When they are weighed in May, do a FEC and correct it for FCS. Then repeat this at the August weighing.
• Use this information to start sorting out a top team. Make up a simple index by adding the two live weights to the fleece weight and put them in order from highest to lowest. Put the FEC corrected for FCS alongside each animal.
• Come down the list looking for individuals with the highest combined weights and Nil FEC. If you can’t achieve nil FEC then go for the next lowest figures.
• See what the numbers look like to meet your needs, aiming to end up with around 20% of the original group to proceed to the two-tooth stage.
  

Two-tooth rams

• When the ram hoggets are two-tooths, things are starting to get exciting and any doubts about the wisdom of starting this exercise should have long gone. They should look a picture!
  
• If they don’t then review what you have done and accept that the challenge may be bigger than you expected. Use this as motivation to do better next season.
• Keep studying the selection list developed above and if you still want to reduce numbers, you can always increase selection pressure by doing another FEC/FCS on the very top ones as a reassurance that they are host resistant.
• Or you could take another live weight.
• Keep culling on structural soundness as there is always a few last-minute cases of footrot or scald injuries. Or teeth going wonky!
• Select a first team to mate with your elite ewes to speed up generation turnover, and make sure they all had nil FEC and FCS of 1 (marbles).
• Keep a second team to mate to the flock ewes – again if possible with nil FEC corrected for FCS. Nil FEC or FCS of 1 has got to be the standard for all two-tooth rams eventually used.
• Graze them now and again in the hay paddock by the road so passers-by and your critics will see them! It will also help challenge the rams’ immunity and host resistance as these paddocks tend to be regularly overstocked and rich in larvae.
• Have an outrageous price ready for anyone brave enough to ask! This is no joke as what is the value of a ram that is very likely to be host resistant to internal parasites with a nil FEC will not grow dags and certainly has never had a drench?
• You may easily get some offers – perhaps from your critics or via your vet from clients who have stopped buying drench because they have ‘hit the wall’ over drench resistance.
  

PATHWAY 3: Selecting males to breed females

Using the two-tooth rams

• This genetic pathway is the ‘power stroke’ in flock improvement because a ram has greater genetic influence than any single female.
• These rams are worth big money and if in doubt, ask yourself where you could buy better ones with proven host resistance to worms and dag-free?
• They have been intensively selected on your farm, so there are no doubts about how their progeny will suit your farming system.
• Their mission is to sire as many future females as possible in the flock to spread their genetic potential for host resistance to worms and dags. They will be delighted to accept the challenge.
• If AI had been a commercial reality, then this would have been the way to use them. But a lot can be done using single-sire natural mating.
• Past experience has shown that in situations like this where genetic improvement is ‘urgent’, top rams can be joined for single–sire mating with 400 ewes for one cycle. You’ll be surprised how many lambs will result. But for more ‘normal’ use- join a ram with 100 ewes.
  

PATHWAY 4: Selecting males to breed males

• This is the final genetic pathway and comes as part of pathway 3.
• The male lambs produced by these top sires will go around the loop again described in Pathway 2.
• Inevitably the top sires of this generation will sire the top sires of the next generation, and breeders often get concerned about the build-up of inbreeding. With a large flock this is not a major problem in the early stages.
• When you become concerned, then one outcross to sheep from a breeder with similar objectives will restore enough genetic variation for you to continue making progress.
• Another method is to divide your main flock into small sub-flocks (on paper) and keep moving rams around these in a planned rotation each year.
  

Final points to ponder

• There is no need to panic! You cannot do any ‘genetic’ harm in your flock, because if you’ve been buying rams from progressive stud breeders in the past, you’ll have enough of their good genetics in your flock to stay where you are.
  
• You should in theory only be a couple of generations behind them.
• You certainly cannot go genetically backwards without some very serious negative selection which would be hard to do. Everything you have done so far is positive!
• With the basic selection programme as outlined, the chances are very high that you’ll go forward on to a new ‘genetic plateau’ – and keep going.
• You have used the four classical ‘genetic pathways’ for flock improvement – and you’ve shown that the dull theory (that has bored so many generations of students) does actually work in practice! Oh if they had only appreciated this when they slept through the lectures!
  

What to do if you hit a crisis?

• This could happen of course – an example would be an unexpected outbreak of Barber’s Pole (Haemonchus contortus) worms or some other species.
• Again don’t panic, as all you need do is use an appropriate conventional drench, and because your sheep have never been drenched and are either resilient and/or resistant, the drench will be highly effective.
• Such an outbreak should be a one-off event and will not compromise your breeding programme. But be vigilant as under the law you cannot compromise animal welfare.
  

Whew! Did you make it?

• Congratulations if you came through all that lot!
• You deserve a plasma-screened TV or an iPod!
• Remember what it was all about - to breed sheep with a high natural (genetic) immunity to internal parasites.
  

Disclaimer This material is provided in good faith for information purposes only, and the author does not accept any liability to any person for actions taken as a result of the information or advice (or the use of such information or advice) provided in these pages.