Farm working Dogs in New Zealand. 6. Common Health Problems

By Dr Clive Dalton

 

Internal parasites

Hook worm (Uncinaria)

About 50% of dogs are infected with hookworm.  Eggs develop in the soil and larvae can burrow through the animal's skin.  They mature inside the dog and are passed out to complete the cycle.   Some dogs have developed a high resistance to hookworm infection and may only show lack of energy when working.

Signs:

*  Unthriftiness.

*  Anaemia.

*  Coma and death. 

Prevention

*  Don't house dogs on dirt floors.

*  Steam-clean kennels and move to clean ground.

*  Keep dogs away from infected areas.

*  Consult your vet for a drenching programme.

   

 Roundworms  (Toxocara canis)

The most common worm in dogs.  Pups get infected by migrating larvae in the bitch's tissue.  Many of them will not show signs of infection but the worms will be there.

Signs:

*  Pot belly.

*  Intermittent diarrhoea.

*  Nervousness.

*  Death in severe cases. 

Prevention

*  Contact vet for appropriate treatment.

*  Treat pups at 2, 4, and 6 weeks of age.

*  Keep a clean kennel.

*  Keep a clean food storage area.

*  Maintain good hygiene with a whelping bitch.

*  Keep young children away from pups in dirty conditions.

  

Whipworm (Trichuris)

Causes inflammation of the caecum. 

Signs

*  Weight loss.

*  Diarrhoea.

*  Get worse as worm burden increases. 

Prevention

*  Check with vet for correct treatment.

*  Regular dosing every 6 months.

  

Fleaworm (Didylidium caninum)

This dog tapeworm grows inside the dog, and the eggs pass out in the faeces.  The flea then eats the eggs which grow into cysts inside the flea.  The dog then eats the flea to complete the cycle.

Signs

*  General unthrift. 

Prevention

*  Check with the vet for a correct diagnosis.

*  Treat the dog by breaking the cycle.

*  Drench the dog every 3 weeks.

*  Treat for fleas.

 Hydatids tapeworms 

There are three tapeworms which come under the common name of "hydatids" tapeworms so it can be confusing.  It's important to know their differences.

 True hydatids  (Echinococcus granulosus)

The main concern here is for human health, and thankfully because of past programmes the incidence of hydatids is very low.  Note though that it is still there and this parasite must be taken seriously.

If dogs eat the untreated offal of sheep, goats, pigs, and cattle, they can ingest cysts which are full of immature tapeworms.  On bursting they grow into small tape worms 3-6mm long in the small intestine of the dog and have little effect on its health. 

When these tapeworms mature their end sections drop off and are full of highly resistant eggs which can live on pasture for several months.  When eaten by an intermediate host (sheep, cow, pig, goat or human), these eggs hatch and develop into slow-growing cysts, usually in the liver and lungs.

The cysts generally don't affect livestock but in humans can grow to 50mm across and can be life threatening.  If a cyst burst inside a person, then the risk of further infection is very high and recovery low.  They face a lifetime of regular surgery to remove them.

 False hydatids (Taenia hydatigena)

This tapeworm lives in the dog and can grow up to 5m long.  The eggs pass out the dog on to pasture and if eaten by sheep, goats, cattle, pigs and deer hatch into larvae which during their migration though the body can damage the liver.  They end up in the abdominal cavity where a cyst up to 10mm in diameter develops..

 Sheep measles (Taenia ovis)

This tapeworm only moves between sheep and dogs.  Human health is not involved.  Although the tapeworm can grow to 1m long inside the dog, it doesn't seem to affect its health.  It has a typical tapeworm life cycle from inside the dog, picked up by grazing sheep as the eggs can last a long time pasture. 

The intermediate stage inside the sheep is where cysts appear in the heart muscle and diaphragm.  Infected carcasses have to be trimmed or rejected for export.  The cysts are hard creamy-white nodules about 5mm across and appear in .  In bad cases they will be all through the big muscles too, looking like an attack of measles.

They are no risk to humans but can put customers off buying lamb for ever.

Prevention of all "hydatids" in dogs

*  Register all dogs.

*  Treat them regularly according to veterinary advice.

*  Prevent all dogs from having contact with dead animals.

*  Don't feed any offal from any farm animal to a dog.  Offal is maybe cheap dog feed             but the risks of infection are too great.

*  Burn or bury all offal.

*  If you feed sheep or goat meat to dogs, either heat it to 72 degrees Celcius for at least an hour, or freeze it at minus 10 degrees C for at least 7 days.

*  Provide dog-proof enclosures for killing dog meat.

*  Provide secure housing for dogs.

  

External parasites 

Fleas

There is an old saying that "fleas are good for dogs, they remind them that they're dogs!"  This is a lie.  Fleas don't breed on dogs, they breed in the dirt and debris of the kennel and surrounding area, where larvae develop into adult fleas.  These then invade the dog and cause great irritation.  Constant scratching can damage the skin and allow secondary problems such as anaemia and loss of condition to arise.

Fleas breed faster in warmer weather - so be on guard in summer and autumn.  Modern flea collars work well with protection for up to 4 months.  It's a good idea to clean up the kennels with insecticide too to reduce the population.  Follow the label with all insecticides.

 Lice

These are common on dogs but don't show much effect.  A really heavy infection will cause anaemia.  Lice only live on the dog so there is no need to treat the kennel area.  Kill the lice on the dog with some of the modern treatments (see your veterinarian) and that will fix the problem.

 Cattle tick (Haemophysalis longicornis)

This is the only tick found in NZ and can be a nuisance on cattle and deer if present in large numbers.  Dogs will easily pick them up during work.  The tick sucks blood, becomes engorged and then drops off.  It's not until the animal is heavily infested that it may be of concern.

Don't pull the ticks off the dog as the head remains in the skin and can cause infection.  They can be removed by kerosene but it's best to treat the dog with a correct insecticide.  Check with your vet.

 Ear mites (Otodectes)

Causes irritation in the dog's ears and may lead to secondary infections by bacteria and fungi.  Consult your vet if your dog is scratching or shaking its ears which can be very sensitive.

 Mange mites

Demodex and Sarcoptes mites are the cause of mange in dogs.  If the dog is scratching a lot, is losing hair and there are secondary skin infections present, then check if mites or consult your vet.  These mites burrow down into the skin and there's a chance that they can infect humans.

So don't delay with treatment, as bad infections can take a long time to eradicate.  DO NOT put the dogs in the sheep swim dip or shower, or use any sheep pour-on treatment.  This could kill the dog.

  

Virus diseases 

Distemper

This can be a very nasty disease in dogs and very distressing for owners as they see their dogs taking fits.  Signs include:

*  Fever.

*  Depression and loss of appetite.

*  Running nose and eyes.

*  Coughing.

*  Scouring.

*  Fits, yelping and twitching.

It's caused by a virus, usually widespread among dogs, and can be picked up from contaminated objects like clothing.  It spreads from dog to dog by moisture from eyes and nose.

Incubation is about 10 days during which the virus affects many organs such as the gut, lungs and brain.  Many dogs (about 50%) develop sufficient antibodies in a couple of weeks to control the disease and recover well.

Dogs with no antibody resistance will die.  Bad cases may recover but the dog may have impaired eyesight for the rest of its days.  It is essential to vaccinate when the dog is 6-8 weeks, 12 weeks and 16 weeks of age.  This is usually combined with parvo vaccination.  Then an annual booster may be needed if the dog isn't in contact with other dogs that challenges its immunity.  Check with your vet for details.

  

Parvovirus

A really distressing disease for both dog and owner.  The virus is excreted in the faeces of infected or carrier dogs and can survive in the environment for some days.  Incubation takes from 1-5 days but it's not certain how it spreads.  These pups become depressed and die.

One form of parvo (Cardiac) affects the heart muscle of pups under 4 months old, and the other (Enteric) is seen in dogs of all ages.  These dogs vomit and have a severe foul-smelling diarrhoea.  Blood may show in the faeces.  The dog will be depressed and run a temperature.

Vaccination against parvo is essential for all pups and is usually tied in with distemper protection.  Consult your vet for details.

  

Infectious hepatitis

Not very common but can be devastating. 

Signs are: 

*  Vomiting and diarrhoea.

*  Fever

*  Thirst

*  Listless

*  Discharge from eyes and nose.

*  Red mucous membranes.

The virus is spread in all the dog's excretions and attacks the liver and other vital organs.  Prevention is by vaccinating young pups and is tied in with distemper and parvo protection.  Consult your vet for directions.

Other viruses

There are many other viruses that can affect dogs and appear as epidemics in districts after introduction by a carrier dog.  So it's a good idea to isolate a new dog for a while to make sure it's not a carrier.  Check what vaccinations a newly purchase dog has had, and discuss vaccination with your vet against these potential problems

New Zealand Sheep Husbandry - Using Refugia to control worms

By Dr Clive Dalton

Refugia – what’s it all about?
The word ‘refugia’ seemed to appear out of the blue about 5-6 years ago, and was used by veterinarians and parasitologists when talking to farmers about worms (internal parasites) in sheep and in cattle.

Finding out about the bad news

• In a survey of sheep and beef farms by Meat & Wool around 2006, it was discovered that worms had become resistant to a range of anthelmintic drenches, and that some urgent action was needed to stop the rot!
• A massive bureaucratic panic resulted with one of the main results being the formation of a programme called ‘Wormwise’ to advise farmers what to do to control worms, and especially how to stop drench resistance increasing.
• Wormwise is still in existence, but with much less panic now as despite dire predictions that no new drenches were in the pipeline, at least two are now on the market which are promoted as solving the resistance problem.

We should have known!

• Drench resistance in worms should not have come as a surprise, as a few lone voices about 30 years ago warned this could happen if we became totally reliant on the new drugs (at that time) to kill worms.
• The worms would outsmart the humans through the simple process of ‘the survival of the fittest’, so that those that became resistant to these chemicals would survive and multiply.
• But then of course – nobody wanted to think too far ahead and about the downside of using chemicals to kill worms, as everybody involved was making money from their widespread use – the big international pharmaceutical companies who made them, the vets and distributors who sold them, and the farmers who used them.
• It was easy (too easy) to believe that predicted problems were only conjecture. It only took 30 -40 years to prove it was fact!

Refugia arose from the insect world

• It was when parasitologists started to describe how worms started to develop resistance that the word refugia appeared, as similar concerns were expressed about insects about 40 years ago when chemicals like DDT were used extensively to kill them. It was a particular concern with mosquitoes in Africa.
• It was predicted and proven true that a population of insects resistant to chemicals could keep on increasing, and one way to stop this was to have a ‘refuge’ where ‘susceptible’ insects could survive (by not spraying) to mate with the resistant ones and thus slow the rate of total resistance in the population.
• Exactly the same situation was described by parasitologists as a possible way to slow up the rate of drench resistance happening in worms in sheep and cattle.

Refugia was a concept
Refugia was and still is a concept – and is by no means a proven solution. It was the only good news that parasitologists could come up with at the time, and it sounded reassuring – to some.

How is refugia supposed to delay drench resistance in worms?

• In the worm life cycle, male and female worms mate in the gut and produce eggs, which go out in the faeces on to the pasture where they live as larvae, then crawl up the grass again and be eaten by the host for the cycle to continue.
• Anthelmintic drenches kill all the worms (some kill the eggs too) that are susceptible to the particular chemical, so they can’t mate and lay eggs.
• So when resistant males mate with resistant female worms, their offspring are not killed and they produce resistant offspring.
• To slow up all worms becoming resistant, we need drench resistant worms to mate with susceptible worms, so a proportion (unknown) of their offspring will be killed by drenching.
• So the more susceptible worms that are in a ‘refugia population’ on the farm, the slower will be the rate of descent toward total drench resistance.

How to keep a refugia population of worms?

• This done by not drenching all the animals in the mob – which used to be best practice before drench resistance was identified.
• Best practice now is to leave ‘a proportion’ of the mob undrenched.
• The size of this proportion is not easy to define – figures like 5, 10, or 15% are suggested, or you should not drench the biggest animals in the mob that are thriving.
• These will be the refuge for worms susceptible to drench chemicals – so will hopefully delay the time when all worms are resistant to chemicals.

Will refugia work?

• Some sheep trials have been done in sheep and showed that drench resistance was slowed up.
• But other sheep work in Australia showed that refugia will only delay the evolution of drench resistance where a large proportion of the worm population escapes exposure to drench chemicals.
• The key thing is that the idea of having a population of worms in a flock susceptible to drench chemicals is a concept which seems to be common sense too.
• It’s simply to avoid as much ‘chemotherapy’ to kill worms as much as possible to delay the day when all worms are genetically resistant.

What’s good for refugia?

• Drench on the basis of a Faecal Egg Count (FEC) and veterinary advice, and not by the calendar.
• Reduce the number of drenches given.
• Extend the intervals between drenches.
• Leave a proportion (5-15%) of the top animals undrenched.
• Concentrate on drenching the poorer-performing animals in the mob.
• Don’t drench mature animals, as their immune system should protect them from worms.

What’s bad for refugia?

• Drenching thinking that this will kill the worm larvae on the pasture. This is a myth.
• Using only one class of stock on an area – you need to mix the species grazing to act as vacuum cleaners for the worms that affect other classes of stock.
• Note sheep and goats share the same species of worms.
• Drenching young animals and then putting them on to clean pasture. This will definitely allow the drench resistant larvae to multiply and when they get back inside the host, to meet other drench resistant worms to keep on multiplying and increasing drench resistance in the flock or herd.

How can you find out if there are drench resistant worms on your farm?

1. Realise that there are many different species of worms, and nto all of them may be resistant to the drenches being used at any one time.
2. Also remember that over 90% of them are in the form of larvae on the paddock and not inside the animal.
3. The test for drench reistance is called a 'Faecal Egg Count Reduction Test' or FECRT/
4. You have to identify a sample of individual animals, then do a FEC to find out their worm burden before drenching them with the particular drench family to be tested.
5. The you do an FEC again, and if the product under test was fully effective, then it should have killed at least 95% of the worms.
6. See your veterinarian for full details of the protocol needed and the costs.

The new drenches

• The two new families of drench chemicals which have appeared on the market work in a different way, and it is stressed that they will kill any worms that have developed resistance to the previous chemicals.
• But parasitologists are warning that care needs to be taken with their use, otherwise we will go down the same track and produce the same resistance problems that has happened before.

Drench resistant worms in sheep – introduction to blog series

By Dr Clive Dalton

This blog series is drawn from the successful plain-language farmer's handbook - Internal parasites of sheep and their control by Dr Clive Dalton (Reward Publishing, ISBN 978-473-12133-4 now in its 3rd edition).

Copies can be obtained from www.lifestyleblock.co.nz or by emailing clive.dalton@gmail.com.




Drench resistance is not just coming - it's here

• Over recent years warnings about the growing disaster of drench resistance in sheep have gained considerable momentum.
  
• The subject has been ‘news’ for both agricultural and general-media journalists.
• The response of most farmers to this has been the wonderful Kiwi response of ‘Yeah Right’, knowing that tomorrow there will be some new crisis the media will urge them to worry about.
• The agricultural media have done a great job in providing information on what is a very complex biological issue.
  
• They have reported helpful comments and advice from veterinary practitioners and researchers, agricultural scientists, farm management consultants and plenty of top farmers about what is going on, and how things should be tackled.
• On top of all this, veterinary pharmaceutical companies have increased information output as well as their advertising and sales promotions.
  
• There has never been as much information available on internal parasites in sheep as there is right now.
• So it’s not surprising that many farmers are confused about what to do while they wait for promised solutions described by enthusiastic researchers as being either ‘close’ or ‘very close’ to fruition.
• As an example of costs, at one time, of the $3.50/stock unit spent on sheep health, $2 is the drench cost so an effective worm control programme is vital to farm profit, and has never been more important than now to appreciate what is reliable information and what is not.
• In May 2005, the first meeting was held to develop a ‘National Internal Parasite Management Strategy’ driven by Meat & Wool New Zealand and the Sustainable Farming Fund.
  
• The ‘Action Plan’ was to run from 2005 to 2008 with the vision to develop ‘effective, sustainable and integrated parasite management for profitable farm enterprises’.
• The main practical outcome from this move was the “Wormwise” programme. Full details can be obtained from M&W NZ, Phone (04) 474-0821. It is a vitally important project for New Zealand’s sheep industry and your comments are always invited.
  

The 'Wormwise' programme

• The main outputs from ‘Wormwise’ are regular newsletters on research and reminders of seasonal issues. Anyone not on the Meat & Wool New Zealand mailing list for Wormwise can register by phoning 0800-696-328 or by emailing wormwise@meatandwoolnz.com.
• This blog provides more background information for farmers (whatever their flock size) to stimulate thinking and hopefully some action to get away from the practice of pouring chemicals down sheeps’ throats. It's a completely independent view.
  
• The blog will also help students of sheep husbandry, veterinary nursing and animal care, as well as those in the farm trading business that have to service farmers. ‘Sustainable Sheep Farming’ must be everybody’s mantra for the future, and at the moment we are not all heading in that direction.
  

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 – 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 resistant worms in sheep – how to test for worm burdens

Sheep, farming, husbandry, health, disease, worms, internal parasites, testing methods

By Dr Clive Dalton

Faecal Egg Count (FEC)

• A good general indicator of a worm burden is the number of eggs passing out of the animal in the faeces.
• This is the basis of a ‘Faecal Egg Count’ or FEC that can be done through a vet clinic or on the farm if you have a microscope and the equipment.
  
• Ask your vet for details, or you can buy a commercially available kit with everything you require plus technical support when needed from FECPAK International Ltd, Box 5057, Dunedin.
• The costs through a veterinary clinic can vary depending on quantity. Some farmers with a FEC kit share the work and cost with neighbours.
• A FEC shows the number of eggs per gram of faeces (epg) and there are accepted ‘trigger levels’ after which you should take action by drenching – or do nothing.
• You cannot tell the worm species from the eggs so to identify species, the eggs have to be incubated in the lab which takes about 10 days and consequently costs more.
• However, the eggs of Nematodirus are larger and very distinctive compared to all other strongyloides worm eggs.
  
• They are always counted separately as Nematodirus worms are not great egg producers so animals can harbour heavy worm burdens and have low (less than 500) epg. This often occurs in lambs.
  

Limitations of a FEC

• A FEC is only a snapshot of the animal’s worm burden judged by egg output at that time of sampling. It’s really a measure of what was going on inside the sheep 3 weeks beforehand.
• With the standard FEC used in the past, the biggest limitation was that samples were not corrected for the Dry Matter intake of the animal or the moisture content of the faeces.
• Despite the limitations of FEC (and still plenty of academic criticism of its interpretations) it’s a very cost-effective tool and in any case it’s the best we have at the moment.
  

Sampling tips

• The easiest way to get a sample is to pick up fresh faeces from the paddock.
• Follow a few sheep around for a while or go where they have been camping and make up a composite sample from at least 5 heaps and better still 10. Mix them well.
• Using composite samples (mixed from a number of sheep) keeps the costs to a minimum. When the lab gets a composite sample it should give it a further good mix before sub sampling, but check that this will be done.
• The more accurate way for the lab to do a composite FEC it for individual samples to be sent to the lab and an equal weight of sample is taken from each, and a special composite FEC carried out to a sensitivity of 10 epg per pooled sample.
  

FEC for genetic selection programmes

Accuracy at the laboratory is very important for
accurate genetic selection decisions

• Here you need FEC samples from individual sheep to make accurate selection decisions.
  
• To do this you can either extract a sample with your finger directly from the sheep’s rectum (wearing a rubber glove), or use a plastic probe which is much faster and more comfortable for the sheep. Contact me for details.
• You can organise a series of small individual pens that you can put sheep in so accurate ID of their faeces can be made after they have passed them naturally.
• Fasting reduces FEC output so epg will be increased; so avoid yarding sheep too early before sampling so their guts are full.
  
• Only bring in enough animals that you can do in 3-4 hours to make the job easier for both human and sheep.
• Also don’t sample too early in the morning – give them a chance to have a good feed before bringing them in. Sample males and females separately.
• Only collect one faecal sample per container, and keep them in a cool place - and not in the family fridge! The farm ‘beer fridge’ is ideal, where they can stay until you go to town. They can remain in the fridge for up to 3 weeks before there is any deterioration. Check that it is set to 4-5ºC.
  

What ‘trigger levels’ should be used?

• A trigger level is the number of eggs per gram of faeces (epg) at which you have to act.
• Above the trigger level you drench, and below it you don’t bother.
  
• The problem is to decide what the trigger level is, and this is not helped by many consultants who dive for cover at the question because of the variables involved in an answer.
• But you have to make a decision, so consider levels below 500 epg to be low, 600-2000 epg to be moderate, and above 2000 epg to be high.
• Key Point: You need to have a different FEC trigger for fattening works’ lambs to those kept for flock replacements where the aim is to put selection pressure on worm resistance.
  
• If you drench lambs with anthelmintics every time they get to 500 epg you’ll certainly make it hard to identify natural (genetic) immunity for worms that needs time and a worm challenge to do this.
  
• For works lambs using 500 epg as trigger is no problem, especially if the drench gives them a lift in growth.
• For breeding decisions, use the FEC of the rams you have used as a reference point. Classify them into groups of below 500, 500-1000, 1000-2000, 2000-3000, 3000-5000 epg, and so on, and see how many are in each group. This would certainly let you see where you were and the size of the challenge to improve things.
  
• It’s no good setting a level of 500 epg if most of your rams are around 10,000 epg. If you don’t know what the rams are, use 1000 epg as a short-term trigger and work to get it down.
  

Faecal Egg Count Reduction Test (FECRT)
This is used to test for drench resistance. It’s a ‘drench check’ where you first drench sheep and then see if the product worked. Some vets recommend that it’s best to sample for FECRT from January – April and not from May – September.

The test is done through a veterinarian using a standard protocol. Here’s one version of it:

• Select a mob of appropriate animals – usually lambs.
• Run them on what you think will be your most contaminated pasture until they have from 500 to 700 epg. Check 2-3 to see when they reach this level.
• Randomly select a group of 10 and individually identify them.
• Do an individual FEC on each of the ten.
• Drench them according to weight with a well-maintained drench gun. Check its accuracy before use.
• The drench used will be from the family you are most concerned about.
• After 7-10 days each animal is re-sampled for FEC.
• If the drench worked, there should have been a reduction of more than 95% in FEC.
• Any surviving worm eggs then need to be cultured to establish their species as they are resistant and dangerous.
  

This is a more costly exercise than just a straight FEC because of the laboratory time and work involved in culturing larvae.

Check with your vet beforehand to ensure you get maximum value from the information and especially advice on the correct drench product and programme to fix the problem – if there is one. The FECRT like all tests is not foolproof, so keep this in mind.


Correcting FEC for consistency (moisture content)

• This is a very important issue so consider it carefully. The research of Dr Leo LeJambre at CSIRO, Armidale in Australia has sorted it out.
  
• He studied the moisture content of faeces, which controls faecal formation and the speed with which faeces pass through the digestive system.
• He reminds us that when FEC was invented by the CSIRO scientists, drying the faeces in the lab was a standard part of the technique.
• It was tedious and slowed up the process so it was gradually dropped over time, and now nobody seems to remember - or have conveniently forgotten!

LeJambre's technique

• It’s very simple. The more moisture in the faeces, then the quicker they pass through the gut, and the more diluted the eggs/gram will be in the faecal sample.
• So unless you correct the FEC for faecal consistency (moisture level), you will make errors in selection.
• A healthy sheep produces faecal “marbles” even when on lush pasture. These are formed in the hind gut where water is extracted and the motions of the gut wall (peristalsis) form the marbles. It’s an amazing bit of physiology.
  

Advantages of faecal marbles to the sheep

Sheep don't get up at nights to go to the toilet - they lie and let it flow! On popular overnight camps they return to the same spot each night to rest. So if they produce marbles, no dung sticks to their wool - so no dags form.

• Marbles don’t stick to wool and form dags. This is especially important during the night when the sheep is lying down and at greater risk of soiling her rear end. They don’t get up to go to the loo!
• Faecal marbles are a sign of an efficient digestive system so such sheep must be converting their feed efficiently.
• If their digestive system is working well, then they are healthy and their immune system must be working well too.
• Spherical faecal marbles have a much greater surface area than the same volume of sloppy dung. It’s about six times greater. So the resident worm larvae die faster though desiccation and radiation – all at no charge to the farm.
• The clusters of marbles soon separate when they dry out, and their dark colour absorbs more UV radiation.
• So faecal marbles are the key to healthy sheep and reducing the larval population on the paddock at the same time, where remember, over 90% of the worm problem resides.
  

How to assess faecal consistency – the Faecal Consistency Score (FCS)
It’s very easy to record the state of the sheep’s faeces when sampling. The Australian researchers have used numerical scores but the following perhaps rather ‘ un-scientific’ descriptions are suggested below (see photographs) as they are easier to remember than numerical scores:

• Photo 1 ‘Marbles’

• Photo 2 ‘Hand grenades

• Photo 3 ‘Plops’

• Photo 4 ‘Slops’

• Photo 5 ‘Scour’

Correction factors used
The corrections used are very simple and again are easy to remember. Multiply the FEC by 1 to 5 as shown below:

• Marbles x 1
• Hand grenades x 2
• Plops x 3
• Slops x 4
• Scour x 5
  

Practical implications of the FCS

• Correcting a FEC for faecal consistency has major implications to improve the accuracy of FEC interpretation, especially when selecting individual animals in breeding programmes.
• For example: When selecting ram hoggets as future sires, if you decided to keep a ram with a FEC of less than 500 epg, you would be fairly happy that he was resistant to worms. But that would only be correct if he was passing marbles.
• If he was scouring, then multiplying his FEC of 500 x 5 would give a 2,500 epg count and you certainly would not want to keep him as a future sire – even though he may be classed as resistant under the old method.
  
• He should be on his way to the dog tucker freezer. The FCS has changed the decision drastically – and surely for the better.
• So not correcting for faecal moisture could lead to a very wrong genetic assessment of replacements (especially rams) for the flock. You could easily end up with high-index daggy sheep that would pass those genes on. That’s not progress!
  

Industry implications of the FCS

• Everybody knows that dags are caused by scouring (faeces with high moisture content) and are the last thing the industry needs with all the extra costs involved of removing them, flystrike, shed-stained wool and contamination of works lambs.
• So by correcting the FEC with the FCS, it’s possible that the confusion caused by retaining low-FEC daggy sheep can be avoided.
  
• The combined FEC and FCS will certainly provide a more accurate selection tool to identify resistant animals in all flocks – stud or commercial. It could be as simple as that!
  

Using FCS to screen ewe lambs/hoggets

• What could be simpler for selecting ewe lambs/hoggets as replacements than keeping those that passed marbles or hand grenades and certainly culling any with loose (high moisture) faeces or are scouring? This simple process could be done any time from June onwards.
• This selection needs to be carried out after the lamb’s immune development has taken place as during this process faecal formations may vary.
  
• By May-June (8-9 months of age) the ewe hoggets that will be dag free in later life should all be producing marbles or hand grenades.
  

What would be the benefits?

• If nothing else, the marbles would reduce larval survival (especially L3) on the pasture through desiccation and radiation.
• So the high pollution rates blamed on lambs, hoggets and two-tooths would be greatly reduced.
• The selected animals would be free of dags and free of costs to remove them.
• The selected sheep would have a high possibility of being resilient or resistant (or both) to worms based on FEC corrected for FCS.
• It would allow large numbers of lambs/hoggets to be checked with no extra work or lab costs as a first initial screening.
  

Some practical challenges

• The idea of screening ewe hoggets or two-tooths on Faecal Consistency Score (FCS) to select worm resistant replacements would have most farmers taking off to the back paddock, and shepherds finding an urgent need to clean under the woolshed!
  
• Here’s three things to consider if you really want to get serious and fix things.

1. You could check each individual animal’s FCS – when it defaecated naturally. This would be a very time-consuming job with a large number of sheep. You’d have to put them on a solid floor, or put some old carpet over the woolshed grating. Put it in the ‘daft idea’ file.
2. Insert your finger into each sheep’s rectum. You don’t need to bring out any faeces to look at it, just remove your finger and inspect the end. This method has been used by NZ Romney breeder Melvin Forlong, and here’s what he does:

• Marbles you can easily feel. Score that FCS 1
• If you can’t feel anything in the hind gut, a hand grenade has just left! Score that FCS 2.
• If your finger end only has a bit of dry green stain on it, score that FCS 3.
• If you finger has more green stain on it and it’s wet, score FCS 4.
• If your finger is covered in green gravy, then score FCS 5

3. You can use a plastic faecal probe which on withdrawal shows the folds of marbles or hand grenades, which contrast with the soft plops, slops or scour. You can do one sheep a minute and it’s a lot less stressful for the sheep and operator. (Contact me for details).

Cheap and quick

• These suggestions are no way near as accurate as doing a proper FEC but they are quick, don’t cost money and would be worth a try as an initial screening.
• Supporting these ideas is the experience of farmers who have always culled daggy sheep (that produce soft faeces) and they’ve made progress in reducing dagging and drenching.
• Culling on FCS could speed up this process as it identifies the problem of dags nearer the source!
  
• Don’t wait for ‘peer reviewed’ research to test these suggestions – you’ll be long gone before anyone gets round to it. Try the ‘probe-it-and-see’ approach.
  

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 – what is drench resistance?

Sheep, farming, husbandry, animal health, worms, internal parasites, drenching, drench resistance

By Dr Clive Dalton

If you are always drenching & dagging, then suspect there may be a drench resistance problem worth investigating

Drench resistance

• Drench resistance is a problem the worms have, and is not a problem with the drench.
• Veterinarians constantly remind us of this as there are plenty of drenches being used that are working perfectly well to control internal parasites. It’s easy to forget this and long may it last.
• Drench resistance is where the worms have developed a resistance to the chemicals in drenches so are not killed by them. This is a ‘genetic’ resistance so the worms have in fact become ‘super worms’ and can pass on their genes to future generations.
• When worms are resistant, at least 95% of them will survive drenching. If the drench works, then no more than 5% should survive if they are susceptible (non-resistant).

Four types of resistance
Four types of resistant worms have been identified. This may seem a bit academic but it could be useful to appreciate the situation on your farm. It’s not a simple picture as there is:

• Single resistance - where the majority of worms are resistant to one drench family. If more than one species of worms is resistant it is called ‘multigenic’ resistance.
• Dual resistance - where some species of worms are resistant to one drench family and other species are resistant to another drench family. BZs and Levs are the only drench families known to be implicated at this stage.
• Multiple resistance - where one or more worm species are resistant to more than one drench family - and possibly all three.
  

Key point: Whilst general resistance knowledge is valuable, it is critical each farmer gains an understanding of the situation on their property.

How big is the problem?

• The full picture is not known but a lot of work is going on to find out. We know it’s an increasing problem on farms that run cattle, sheep and goats.
• Estimates vary about the current situation. Generally it seems that on most sheep farms worm resistance to drench has developed to at least one drench family; and more than half have resistance to two.
• Results from a 2005 survey have shown that drench resistance in sheep to the three broad spectrum chemical families is 61% for Benzimidazoles (BZ or white drench), 31% for Levamisoles (Levs or clear drench), 34% for Ivermectins (Ectins) and 10% for Levs + BZs.
• The conclusion from this survey was that drench resistance is real and is widespread, and measures need to be taken to combat it and certainly prevent its spread.
• The major concern at the moment is that so many farmers don’t know the drench resistance status of the worms in their sheep, and they seem in no hurry to find this out.
• A survey showed that only about 20% of farmers have tested for worm resistance to the drench they are using, and half of these have only done one test so many are still relying on the old advice to prevent problems, and it won’t any more.
• The table below shows more information from the 2005 survey. It shows in a very clear way how drench resistance has appeared in all major internal parasites of sheep to all three broad-spectrum drench families. This is the sort of information farmers need to know for their particular farms, to manage their drenching programme.
  

Frequency of worm resistance found to different drench actives for some parasite species in sheep.

How has drench resistance developed?

• Anthelmintics were introduced in the 1960s and resistance to benzimidazole was first discovered around 1980. Warnings about the long-term consequences of using these new chemicals were aired by some scientists and veterinarians after that, but were ignored by most.
• In 1980 there was even concern voiced in Australia about anthelmintic medications and their bad effect getting through into the ecosystem after they had gone through highly-stocked sheep. Nothing was heard of it again!
• Worms that survive drenching mate with other fellow survivors, and produce mainly drench-resistant offspring which then have a ‘reproductive advantage’ because they have the place to themselves!
• The longer time resistant parasites enjoy a reproductive advantage, the faster drench resistance will develop, but the rate at which this happens varies widely because there are so many variables involved.
• The problem has developed by the ‘survival of the fittest’ among the resistant worms, and the speed of their genetic gain for resistance (to some chemicals) has been remarkable.
• Resistance to a chemical family has developed within a few years on some farms, but on others that have used the same chemical family for a similar length of time or longer and there is no sign of it yet.
• The more times an animal is drenched, the longer the drench-resistant worms will have a reproductive advantage.
• Once the worm population on a farm has become resistant to drench chemicals, this is permanent and worms will not become ‘susceptible’ again. This is the current belief in Australasia anyway.
• In the old days when farmers were advised to change drench families each year, we believed that after a rest period, the worms would become susceptible again. This practice is now classed as bad advice.
• In the 1970s and 1980s it was seen as good farm accounting practice to pay as little tax as possible. Buying drench was a great way to use up surplus cash so woolsheds were full of drums - which then had to be used up. The promotions that went along with the brands certainly encouraged bulk purchase.
• Monday was always a bad day for head shepherds. Their staff were keen to give their dogs a run as they’d been tied up all weekend and were going crazy for work. The head shepherds asked their bosses what was to be done and they had no plans either. The solution was easy - ‘drench the hoggets’. Then everyone was happy except the susceptible worms!
• When long-acting and persistent drenches came along, they were seen as a great idea, especially for ewes to reduce scouring and dagging. Long-acting products are now seen as a fast-track to creating drench-resistant worms.
• There is now growing acceptance that drenching adult ewes that are carrying resistant worms is also a fast-track to increasing drench resistance.
  

Key points:

• Every farm is different and making general assumptions is dangerous.
• In the Farm Case Study – notice that within each family of drench, not all the species of worms have the same level or resistance.
• So this again reinforces the point that you really must know the situation on your farm, and not just grab the first drench container from the shed that rattles before heading for the yards.
  

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.