Mar 142012
 
scottish lamb
 

Worms in sheep, ewes, and lambs on your smallholding

Its March and our ewes will soon be lambing.  Amongst other health issues worms can and will play a part in the fitness of my ewes and lambs over the coming months.  This is a complex area and it can often take smallholders a long time to learn about.  Looking back, I wish I had known all about it before I had got my own sheep or let anyone else graze their sheep on my land.  It would have saved a lot of expense and effort for both myself and the woolly lawnmowers.
 

*checkout the parasite forecast here*

 

 

Are worms harmful to sheep?

If not treated then the short answer is yes.  Most sheep have some worms in their digestive system – this is normal. Indeed, exposure to worms is essential if sheep are to develop and maintain an immunity to worms.  However failure to manage this issue can cause a smallholder a lot of problems and ongoing expense.
“There are three broad types of internal parasite that can cause significant health issues in sheep – worms, flukes and protozoa.” 
 Worm infestation is probably the most common cause of “ill thrift” in sheep. Worm infection is a significant animal welfare issue and, if not treated, can cause death.  Resistance to chemical treatments is also an emerging problem in managing sheep worms.
“Worms are thought to cost sheep owners more than any other disease.”
How much harm worms do to sheep depends on a range of factors:
•  The type of worm
•  The number of worms in the animal
•  The breed of sheep
•  The level of nutrition available
•  The age of the animal and the level of previous exposure of the animal to the specific worms.
It is important that everyone with sheep has a worm management plan – and this includes smallholders. An effective plan is simple and will save a lot of money, effort and heartache.
 

Are sheep worms different?

The short answer is yes.  The life cycles of worms or nematodes are similar – the adult lays eggs in the sheep that pass out in faeces and hatch. The larvae infest the pasture and are taken up by grazing sheep, developing into adults in the intestine.
Teladorsagia, Trichostrongylus and Haemonchus have life cycles of just a few weeks, so several can occur in one season. For example, Haemonchus has a short life cycle – as little as 14 days – so numbers can build quickly.
The life cycle of Nematodirus is a full year – eggs shed by lambs during one spring – hatch the following season to infect the subsequent batch of lambs. The  eggs need a period of cold weather followed by warmer temperatures of 10C or more before they hatch. If conditions are right, this can trigger a mass hatch just when young lambs are starting to graze and the result can be devastating.
 

How do I control worms in my sheep?

Good practice says that a worm management plan is required.  This includes:
  • Worm testing. It is cheap and easy to do. Without regular testing, you won’t know whether you have a problem, whether your worm management plan is working or whether you have an emerging drench resistance problem on your property.
  • Grazing strategy to create safe or low contaminant pastures for lamb weaners and lambing ewes.
  • Maintaining good nutrition during periods of poor pasture growth.
  • Building worm resistance in the flock.
  • Biosecurity measures for new sheep arrivals on the property or any outbreak of worm disease in your flock (a sure sign that your worm management plan has failed).
  • Minimising the risk of drench resistance developing on your property.
 

What is the sign of worms in sheep?

  • A typical sign of a worm problem is unthrifty sheep. One that is not eating properly, is losing condition, tends to lag behind the others when moved and, in severe cases, is clearly weak.
  • A worm problem often (but not always) results in sheep scouring and requires dagging. In severe cases, affected sheep may scour profusely.
  • Not all worms cause scouring (diarrhoea) and not all scouring is caused by worms (can be bacterial/green feed scours, etc.).
  • Other signs of worm infection you may see are anaemia or swelling under the jaw (commonly called “bottlejaw”).
 

Which sheep are more vulnerable to worms?

  • Young sheep (under 12 months old) are far more susceptible to worms (especially  Nematodirus) than older sheep. 
  • Sheep under stress (eg during the later stages of pregnancy, during lactation, during winter feed shortages) are also more susceptible to worms.
  • Sheep in intensive conditions, such as an overstocked under rotated smallholder pasture.
Sheep under twelve months of age and ewes in late pregnancy or lactation have a higher requirement for protein. Weaners need it for their own rapid growth and ewes need it for the growth of the foetus, particularly in the last six weeks of pregnancy, and for milk production after the lamb is born.
If pasture quality is poor, such as during a prolonged period of cold, wet conditions, even healthy weaners or pregnant/lactating ewes have difficulty getting enough protein from grazing. If they have a worm infection, the problem is much worse. In short, they will have a major protein deficiency and this will result in rapid loss of condition, which in turn further increases their susceptibility to worms.
 

What types of Sheep are Less Susceptible to Worms

  • Older sheep (ie sheep that are over 15 months and fully grown) are much less susceptible to worms than weaners and lambs.
  • Wethers and dry ewes are less susceptible to worms than pregnant or lactating ewes.
  • Some breeds of sheep are less susceptible to worms than others. 
If you suspect a worm problem, it is worth doing a worm test to confirm it. However, by the time you have seen the symptoms, the damage to performance has been done, so worms need to be controlled before clinical signs are evident.
 

Worm Control – General Principles

 “Worms are only a problem if the numbers increase to the point at which growth is affected, sheep become susceptible to other diseases, or die.”
There are five components of an effective worm control program.
Drenching alone will not resolve a worm problem. Too frequent drenching with chemical treatments may reduce the sheep’s immunity to worms and increase the problem of drench resistant worms. Ad hoc or over-frequent drenching is one of the major causes of drench resistance and is, in most cases, a waste of money, time and effort.
The overall purpose of a worm control program should be to minimise production losses caused by internal parasites and to maximise the sheep’s immunity to worms. If these are achieved, the sheep will need fewer drenches.

 

What Can You Do to Delay the Onset of Drench Resistance on your smallholding?

Make absolutely sure you are administering the correct dose. Underdosing is one of the major causes of drench resistance, as it helps the worms develop a drench resistance. Check the required dose on the label on the drench container.
Always set the dose by the weight of the heaviest sheep in the flock. Many smallholders just take a guess at this, but if it is possible acquire or borrow a weigh machine that gives you an accurate weight.  Administer this dose to all adult sheep. If the flock includes lambs, set the dose for all lambs by the weight of the heaviest lamb. 
Use the correct drenching technique. In particular, ensure that you are drenching over the tongue rather than squirting the drench into the front of the mouth. If you have just two or three sheep, and if you do not have access to a drenching gun, the drench can be administered via a syringe (with the needle removed) in much the same way as if you were using a drenching gun.
However, when using this method, it is important that the drench is administered slowly, as you are not delivering the drench down the sheep’s throat and are relying on the sheep to, in effect, drink it. After use, the syringe should be cleaned by pumping cold water through it, if you intend to re-use it for future drenching.
 

Tip for maximising the effect of white wormer or drenches on sheep

Fasting. When using white drenches (BZs) or mectins (MLs), the treatment is generally more effective if the sheep are fasted for 24 hours beforehand. Keeping the sheep off feed for six hours after drenching also helps make the treatment more effective.
* ewes in the last six weeks of pregnancy, sheep in poor condition or stressed sheep should not be fasted at all*
Overdosing will not help. However, with white drenches (BZs), two drenches twelve hours apart can be effective. (This applies to sheep but not to goats). Note that any departures from label recommendations will extend the withholding period.
After drenching, put the sheep onto clean pasture wherever possible.
 

Common smallholder mistake about worming

Because many smallholders only have a few sheep or purchase quantities that create an excessive it is tempting to continue to use your wormer until it is finished.  This could lead to the development of resistance within the worms on your ground.  
“Rotate between the drench classes (BZs, LEVs, MLs) either at each treatment or each year.”
Use a worm test to monitor worm faecal egg counts (FECs). If you know the level of worms in your sheep, you will be best placed to avoid drench overuse, slow the development of drench resistance and save on drench costs.
If you suspect drench resistance among your flock, do a drench resistance test. This will show you if any of the classes of drench are ineffective in your situation, in which case they should be dropped from your worm control program. If you wish to undertake resistance testing, discuss the process with your vet.
It is most important that drenching is not the only strategy for worm control on your property. Drenching should be just part of a program that includes pasture management, nutrition and selective breeding of worm-resistant sheep.
 

Herbal alternative to using chemicals to control worms

Below are some suggestions around using herbs etc to expell worms, this can be done along side chemical wormers or instead off where the worm burden is not excessive.  Please note however that these solutions are not effective against fluke and their use is being highlighted as a result of interest rather than fact.  It is known that sheep seek out certain plants when they are available, and it is thought that one of the reasons they do this is to expel worms from their system.
It is useful when using worm expellers to keep your sheep on hard standing for up to 48 hours after treatment.  Herbal expellers can be given to sheep in the form of a drench, in their feed, or through licks or drink. The other option is to include herbage such as chickory and plantain in the seed mix within the grazing.
Plants that have been highlighted as useful in tackling worms are:
  • chickory
  • plantain
  • willow bark (tannin levels)
  • parsley
  • thyme
  • garlic
  • cider vinegar
 

The dangers of introducing new sheep to your smallholder flock

All sheep that are bought in should undergo a quarantine period on arrival. They should be drenched . Following a 24-48 hour quarantine period, all of the susceptible worms should have been passed, the sheep should then be grazed on pasture recently used by the current flock so that they pick up the resident worms on the holding.
Use a “quarantine drench” to treat any sheep coming onto the property. Unless you know the drench resistance status of these new sheep, the most effective “quarantine drench” is a combination drench (ie one containing both white and clear drenches) plus moxidectin, or otherwise just one of the mectins.
Some authorities recommend maintaining a “refugia” of susceptible worms within a flock as a way of delaying any onset of drench resistance. Essentially, this involves leaving some susceptible worms (ie susceptible to your drench providing you know that the class of drench you are using is effective on your property) in the flock. The point is to dilute the number of drench-resistant worms building up in the flock.
“This strategy involves simply leaving 5-10% of the flock undrenched. Of course, the ones you do not drench must be the healthiest looking sheep in the flock.”
There is some controversy about this “refugia” strategy and it may not be appropriate in all circumstances, so please consult your vet before using it.
 

How to use your ground/field/pasture in managing your worm burden

The life cycle of worms includes a period in which the worm larvae live outside the sheep – that is, in the pasture. This creates both a problem and an opportunity for sheep owners. 
 

Sheep worm myth

There was once a common belief that worm larvae could only live outside the sheep for a short time and that destocking a pasture for 3 or 4 weeks was effective in breaking the worm cycle. We now know that larvae can survive on pasture for longer than that, especially where conditions are generally cooler and wetter. In general terms, the higher the rainfall and the cooler the conditions, the longer the larvae can survive in the pasture. 
“If a field/pasture/paddock is cropped or cut for hay or silage, worm larvae numbers are dramatically reduced.”
 

Effect of seasons on worm types

Species of worms change in predominance from the cooler months to the warmer ones. Drenches that may be effective against the cool season species may be less effective against the ones which predominate in the warmer seasons.
 

Reinfection

After dosing, sheep should be put onto dirty pasture to pick up resident worms to dilute the resistant worms that have survived dosing.
 

Mineral/vitamin deficiencies on your ground and in your flock and how this impacts on the sheep worm burden

Research has indicated that the supplementary feeding of certain minerals, where they are already deficient on your property, may increase the resistance of sheep to worms. Research has shown that the supplementary feeding of oats during a period of poor pasture growth (typically winter and sometimes early spring), when combined with high quality pasture management, can improve significantly the sheep’s resistance to worms.
Research has also shown that improved energy nutrition can increase a sheep’s “resilience” to worm infection, allowing animals to maintain growth rates and milk production even if they have a worm infection. When a pasture is in a period of poor growth, energy nutrition can be improved by the supplementary feeding of grains such as oats, barley and lupins. Note, however, that a sudden introduction of grain into their diet can kill sheep. Grains need to be introduced gradually.
 

Liver Fluke in sheep

There are two conditions that have to be met for sheep to be at risk of Liver Fluke Disease (fasciolosis). Firstly, they must graze an area that is constantly damp. Secondly, freshwater snails must be present in that area to act as intermediate hosts for the liver fluke.
 

What are the signs of liver fluke?

The signs of Liver Fluke Disease are weight loss and anaemia. In chronic cases, scouring often occurs (but not always) and the sheep suffers obvious abdominal pain and is reluctant to move. Infected sheep may also develop “bottle jaw” – a swelling under the bottom jaw. Unfortunately, in some cases, there are no obvious signs before the sudden death of the infected sheep.
“Liver Fluke Disease is more likely to occur in summer and early autumn.”
Drenching can be an effective means of preventing Liver Fluke Disease. Note, however, that most worm drenches do not contain a flukicide (ie a drench specifically for the treatment of liver fluke), so check the label to ensure that the drench you are using is registered as a treatment for liver fluke.
Drenching with a flukicide is typically carried out three times a year (late winter or early spring, summer and late autumn). Drenching more often than needed is expensive and may lead to drench resistance. Normally, drenching is only necessary for sheep that graze paddocks with fluke-prone (ie constantly moist) areas. 

Triclabendazole is highly effective at killing all stages of flukes responsible for acute fasciolosis. Drenched sheep should be moved to clean pasture or re-treated every three weeks for the next three months at least as prescribed by your veterinary surgeon.  Nitroxynil and oxyclosanide are less effective against immature flukes and should be used only in the treatment of subacute and chronic fasciolosis. Once again, treated sheep must be moved to clean pastures.  Improved nutrition is essential.

Draining or fencing off fluke-prone areas will help reduce the risk of liver fluke disease. Chemical control of snails in fluke-prone areas is generally a poor option. Snails reproduce very quickly and will repopulate treated areas. And the use of poisons so close to waterways is likely to be dangerous to the aquatic environment. For a small additional cost, you can check for the presence of liver fluke when you do a Worm Test.
websites used in the making of this post:
  • Drenching http://www.dpiw.tas.gov.au/inter.nsf/webpages/cart-6396qk?open
  • http://www.fwi.co.uk/academy/article/126167/worms-in-sheep.html
  • organic http://www.skylinesfarm.com/parasitecontrol.htm
  • herbs for worming http://reedbird.com/articles/herbsfordeworming.html http://lavenderfleece.com/herbals.html
  • http://www.smallstock.info/tools/disease-nutrition/7424.htm

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