Woolshed 1: January 2009

January 31, 2009

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.

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?

If ‘YES’, then get your veterinarian or consultant to work out a strategy to continue farming your sheep sustainably.
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.
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?

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.

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.
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.

January 29, 2009

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.

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.

Drench resistant worms in sheep - resilience and resistance

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

By Dr Clive Dalton

Resilience & resistance

These terms appeared only recently on the farming scene from the research world, and without a lot of explanation.
They sneaked up on us so it’s not surprising that some farmers are a bit skeptical that the issue has been made overly complicated by academics.
The two terms are different concepts and it’s important to understand the difference between them to farm sheep sustainably.
Veterinarians, consultants and ram breeders are certainly using these terms now – and hopefully they all agree on their meaning. It doesn't always seem to be the case.

There are three parts to the story. You can have:

Resilient animals
Resistant animals
Resistant worms

1. Resilient animals

The term ‘resilience’ is straight forward as it only applies to the sheep. It’s sometimes called ‘host resilience’ but ignore this as there is enough confusion.
The main thing is that resilient animals can tolerate a worm burden and still keep on producing well. They need less drench but they still contaminate pasture with worm eggs. This is very important.
Note that resilient animals are not themselves resistant to worms – they only tolerate them without any ill effects.
It’s when the worms in resilient animals become resistant to chemicals that things get difficult, as they are still producing eggs in large numbers.
You may see the word ‘tolerance’ used to describe resilience. Don’t use it either to avoid more confusion.
Geneticists state that resilience as a genetic trait is complex and weakly inherited. Heritability estimates of 5-15% have been published.
Key point: Note that a so-called resilient animal can carry both resistant worms and non-resistant (susceptible) worms, and the only way to find out which is present is to do a ‘Faecal Egg Count Reduction Test’ (FECRT) (see later).

2. Resistant animals (host resistance)

Resistant animals have developed immunity to their parasites so have lower worm burdens and hence they have lowered FECs.
Resistant animals do two things. They are able to prevent the establishment of worms in their system, and then evict any that do establish. They pass fewer and less-viable worm eggs on to the pasture, and this helps even more to break the parasite life cycle.
Worm resistance as a genetic trait has been shown to have a heritability of 23-25%. This is in the medium range of traits but is high enough to say that good progress will be made if you generate enough selection pressure (Selection Differential) on both the male and female side. Traits with high heritability are lamb growth (38-48%), fleece weight and FE resistance (30-40), and fleece weight (50-80%).
The other good thing about resistance is that it also has a high ‘repeatability’. This means that once you measure resistance and find animals that are high, they should always remain high. This is especially useful for early identification of replacement breeding stock.
Animals with high genetic resistance to worms are said to produce more dags, because it is stated they produce excess mucus to flush the parasites out of the intestine. Be wary of this statement.
Key point: Use the term ‘host resistance’ to describe these resistant animals, then you won’t get confused with resistant worms.

3. Resistant worms

These are simply the worms that through a ‘reproductive advantage’ or ‘survival of the fittest’ have multiplied to large numbers to dominate the population.
Research so far shows that once they become resistant to drench chemicals they stay resistant.

Changing from resilience to resistance
There’s a lot of conjecture about this. Here’s some points you hear discussed.

We know that milk lambs can handle quite high worm burdens (above 10,000 epg) while still on the ewes, but then problems occur once they are weaned.
So from this you hear comments that lambs start out being resilient and then once their immunity develops (and their FEC drops to below 500 epg), they can be considered to be resistant.
If a lamb didn’t get below 500 epg and remained at 1000 epg, then it would remain resilient - in good health and happy to live with it’s worm burden.
All this is a nice concept but things are probably much more complex. Resilience and resistance could be the two ends of the same thing, but don’t hold your breath until it’s sorted out as I doubt if it’s even on researchers’ ‘to-do’ list.

Why would anyone want resilience?

Resilience is a daft goal.
Who would want sheep that maybe could live with a worm burden, but polluted pasture with larvae that we now know can live for long periods and even go down to 10-15cm in the soil when things get tough up top?
And the chances are also very high that they’d be great producers of dags.
With a resilient flock, imagine the words you’d need to instruct the auctioneer before he asks for an opening bid on your lambs in future.
Or worse still, what are you going to tell the prospective buyer of your farm when the day comes to sell and he/she asks about the drench resistance status.
And if you don’t sell and pass the farm on to a family member, what a great heirloom resilient worms will be to deal with. It would justify a plaque in the woolshed where the dags are laid out to dry commemorating your generosity!
So don’t complicate life by worrying about resilience. Ignore it.

Resilience as a breeding objective

Resilience as a breeding objective is daft!
Why would anyone want to farm sheep that maybe perform OK with a gut full of worms, but pollute the farm with larvae that are hard to kill in the environment?
Add to that the chances that their progeny for the whole five years in the flock will need to be dagged at least once every year, if not twice.
Breeding for resistance is the only way to go.
I suspect the difference between resilience and resistance has been made in to a big issue by academics, and not by sheep or their worms.

Drench resistant worms in sheep - refugia

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

By Dr Clive Dalton

What is 'refugia'?

The word ‘refugia’ appeared out of the blue with no explanation of where it came from. It has been around academia since at least 1976 when it was posed in relation to insect populations in Africa becoming resistant to insecticides.
Researchers talked about insects being ‘in refugia’ so now we talk about internal parasites being in refugia.
The academic definition of refugia is ‘the proportion of a worm population that cycles (breeds) and is not exposed to a particular drench chemical, so escapes genetic selection for resistance’.
The concept is very simple. Think of it as worms in a refuge hopefully avoiding resistance.
You don’t want worms inside the sheep or larvae on the paddock that are not killed by a drench. If you keep on drenching, the susceptible worms will die and the resistant ones will survive and breed.
So you need to keep a population of ‘susceptibles’ in the system somewhere, to keep on breeding with susceptibles which will then be killed by drench.
But you also want the susceptibles to breed with resistant worms to slow up their resistance developing, and hopefully be killed by drenching too. Let’s hope the crossbred don’t show hybrid vigour.
In 1981 researchers at Armidale pointed out that refugia will only delay the evolution of resistance where a large proportion of the population escapes exposure to the anthelmintic so the population continues to consist of mainly susceptible worms.
It’s important to keep remembering this.

The dilemma !
There's always a dilemma.

If you drench to kill worms in a flock to improve health and production (which is all good), then you cannot expect the flock to have a large population of worms in refugia especially as larvae on the paddock.
With extensive drenching you will end up with a large population of resistant worms as larvae on the paddock (which is not good) as you have killed all the susceptible ones.
As the refugia population cannot be measured, this means that things will vary a great deal, and it will change greatly between years and between farms.
The fear is that it may only be a very short-term solution in some flocks depending on how far drench resistance has developed.

What’s good for refugia?

Reduce the number of drenches given.
Extend the intervals between drenches.
Leave around 5-10 % of top lambs in a group undrenched.
Not to drench any animals in the top end of a mob, or only drench the tail-enders.
Not to drench animals above 12-18 months old as their immune system should be fully developed.

What’s bad for refugia?

Remember the dilemma. What’s good for worm control is bad for refugia.
Drenching animals on to a ‘clean’ pasture as this will allow the resistant worms to multiply.
Using only one class of stock on a paddock that are regularly drenched.

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.

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?

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January 31, 2009

January 29, 2009