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Home Worm Control Program – NSW non-seasonal rainfall Appendices: Further Information on Sheep Worm Control for NSW Non-Seasonal Rainfall Region

Appendices: Further Information on Sheep Worm Control for NSW Non-Seasonal Rainfall Region

Liver fluke control

Liver fluke (Fasciola hepatica) only occurs where the intermediate host (lymnaeid snails) are present. These snails are found where there are slow-moving creeks, swamps or springs and they can survive in mud when water flow temporarily stops. However, the snail is not necessarily present in all such areas.

Liver fluke may not be present on all paddocks or properties in a ‘flukey’ locality.

Roundworms are often specific to one type of animal, but liver fluke can infect many species including cattle, sheep, goats, alpacas and horses, as well as humans and wild animals


Grazing management can help prevent liver fluke infection. Unfortunately, there is currently no effective method to breed for host resistance to liver fluke.

If liver fluke is present on a property, infection can be prevented or minimised by

  • isolating the areas that harbour the snail, using fencing
  • conducting earthworks to deepen shallow water, or to improve drainage
  • repairing broken pipes and troughs that have resulted in permanent wet areas
  • avoiding grazing of snail-infested areas by the most susceptible animals (sheep, goats, alpacas and young cattle)


Testing for liver fluke can be done using the dung samples sent for a WormTest. A fluke test, which uses a different method to that used for roundworms, must be specifically requested.

If you don’t know whether your sheep are infected with liver fluke, test three times a year (autumn, winter and summer) for at least two years (i.e. 6 tests).

Testing will show whether liver fluke is present and to what extent.

You can also determine which paddocks are affected by testing mobs that have only been run in a particular paddock since the last fluke-treatment.

If fluke egg counts for a particular paddock are frequently high (greater than 25–50 eggs per gram), there may be significant production losses. Reconsider your grazing strategies for the affected paddocks and see if fluke- affected areas can be fenced off.

If results at the three testing times are not always positive, then continue testing at the specified times to decide whether to drench.

If all six tests have been negative and the livers of dead or slaughter sheep have not shown any signs of liver fluke, it is likely that the lymnaeid snails are not present on your property to act as a host for liver fluke.

Drenching for fluke will not be required (except to remove fluke from sheep brought onto the property).

A blood test (antibody [ELISA] test) is also available from various laboratories, for example, the NSW Department of Primary Industries State Veterinary Laboratory at Menangle. Also, a faecal antigen test for fluke is available from there, as well as through Charles Sturt University’s Veterinary Diagnostic Laboratory.


Any positive fluke egg count is significant and indicates treatment is needed.

If testing for two years confirms that sheep are infected at all test times, then ongoing testing can be stopped. In this case, three routine treatments for liver fluke should be given to sheep that have been grazing the affected paddocks in

  • April–May
  • August–September
  • February

Some treatments for roundworms (scour worms and Barber’s Pole worms) will control various stages of liver fluke. Check the label as some are only effective against mature fluke (see Table 1.).

The most important treatment is carried out in April–May and should be based on the flukicide, triclabendazole, which is effective against all stages of the fluke found in the sheep. If treatments are also required in August– September and/or February, one or both of these treatments should be a flukicide other than triclabendazole (if this was used in April). This treatment rotation will reduce the rate of development of fluke resistant to triclabendazole.

Flukicide resistance is common but not well-documented. A follow-up fluke egg count conducted 30 days after the April-May or the August treatment will indicate if the fluke have survived the flukicide.

When bringing in sheep from another property, consider including a fluke treatment in the quarantine drench if their fluke status is unknown. Bear in mind that adult liver fluke can live for several years inside host animals.

Table1.Fluke treatments and the age of fluke from which they are effective

Active Age of fluke killed
Triclabendazole All stages
Albendazole From 12 weeks
Closantel From 8 weeks
Closantel plus oxfendazole From 6 weeks
Closantel plus albendazole From 8 weeks
Oxyclozanide plus levamisole From 12 weeks
Source: from Liver fluke disease in sheep and cattle, by J Boray (March 2007) NSW DPI Primefact 446

The following drench actives do not control liver fluke:

  • moxidectin, abamectin or ivermectin
  • oxfendazole and fenbendazole
  • levamisole
  • naphthalophos and pyraclofos
  • monepantel
  • derquantel
  • praziquantel

Resistance to flukicides

Resistance has developed to various flukicides. Rotate between flukicides from different chemical groups, beginning with triclabendazole for the April–May treatment.

Resistance of liver flukes to flukicides can be checked, however, fluke egg counts may not be high enough to give a precise estimate of flukicide efficacy, nevertheless, they are still worth doing. You will need a fluke count carried out not long prior to drenching (up to 2 weeks before administering a fluke drench). Follow this up with another fluke count between 21 and 28 days after the fluke drench was given. If your flukicide is effective the fluke egg count will normally go down by at least 90%.

More detailed information on liver fluke can be found at the NSW DPI web site: Liver fluke disease in sheep and cattle

Roundworm life cycle and larval survival

Figure1. The life cycle of sheep roundworms (source – Sheep CRC)


Figure 2. Modeled from death rate of the L3 population in ‘Simulation of pasture larval populations of Haemonchus contortus’ by IA Barger, PR Benyon & WH Southcott. Proceedings of the Australian Society of Animal Production (1972) 9: 38

Factors contributing to paddock contamination with worms

The following table applies to:

Factor Time or conditions Effect
Minimum time before worm eggs can become infective larvae. 4–10 days Short graze periods (less than 4 days) prevent ‘auto-infection’ (animals becoming infected by larvae arising from worm eggs the same mob have recently deposited onto the pasture).
Conditions required for significant numbers of worm eggs to hatch and become infective larvae. 4–10 days of:
Brown stomach worm
Temperature: daily maximum >8°C1
Moisture in this time: >10–15 mm rainfall2
Black scour worm
Temperature: daily maximum >15°C for
T. colubriformis or >12°C for T. vitrinus
Moisture in this time: >10–15 mm rainfall3
Barber’s pole worm
Temperature: daily maximum >18°C1
Unsuitable conditions prevent eggs hatching and developing into infective larvae.
Note: The eggs of the brown stomach worm are much more tolerant of cold and dry conditions, and in general, grazing management has less effect on its control.
Moisture in this time: >10–15 mm rainfall3
1Some hatching of worm eggs of all worm species can occur below these daily maximum levels, but this is usually at a small and insignificant rate.
2Brown stomach worm eggs can develop at low rates without rainfall even in a relatively dry faecal pellet.
3Development to infective larvae may occur without rainfall if soil moisture profile is high.
Maximum time worm eggs can live awaiting suitable hatching conditions. Brown stomach worm: 21 days
(Note that some brown stomach worm eggs may survive for longer periods)
Black scour worm: 16 days
Barber’s pole worm: 5 days
Prolonged periods without the right conditions (temperature/moisture) for egg development will result in the eggs dying. This lowers the worm-risk of paddocks.
However, once hatched, infective larvae of both black scour and brown stomach worm can remain in the faecal pellet until conditions are more suitable.
The time for about 90% of the barber’s pole worm infective larvae (L3s) to die (making paddocks low worm-risk).
Note: larvae of brown stomach worm and black scour worm can survive longer because they can remain in the faecal pellet for extended periods.
Cold – Maximum temperature: < 15℃
Time for 90% larvae to die: 4 months
Warm – Maximum temperature: about 22℃
Time for 90% larvae to die: 3 months
Hot – Maximum temperature: about 35℃
Time for 90% larvae to die: 1.5 months
Very Hot – Maximum temperature: > 40℃
Time for 90% larvae to die: 1–2 weeks
L3 larvae do not feed. While waiting to be eaten by animals, they wriggle randomly in drops of moisture, more so in warmer conditions. Increased activity in warm weather depletes their energy reserves faster, hastening death.
In extremely hot, dry and windy conditions the larvae dry out and die.
Minimum time for infective larvae eaten by animals to mature and lay eggs (the ‘pre-patent period’). Sheep: minimum of 18 days for most sheep roundworms.
Goats: minimum of 14 (typically 21) days for barber’s pole worm and 21 days for scour worms.
Worm larvae eaten by animals soon after an effective drench will take at least 18 days (in sheep) or 14–21 days (in goats) before they can lay eggs. During this period after administering an effective drench, animals are not re-infecting the pasture.

Smart grazing for weaner worm control

By Norman Anderson & John Larsen, Mackinnon Project, University of Melbourne

From the Mackinnon Project website (10 December 2011): http://www.mackinnonproject.com.au/index.php?option=com_content&view=article&id=65&Itemid=1


Smart grazing is an improved yet simple and reliable strategy for the control of worms in weaner sheep during their first winter. It can counter the negative effects of summer rainfall that reduces the effectiveness of the ‘2­‐ summer treatment strategy’ in the winter rainfall areas of southern Australia.

The why and how of ‘Smartgrazing’

Merino weaners are very susceptible to worms in their first winter. Consequently, they need to graze pastures that have as few worm larvae as is practicable. ‘Smart grazing’ combines intensive grazing for 30 days with each of the 2 ‘summer’ drenches to ensure that virtually no worm eggs are deposited on a chosen pasture from the first summer drench (November) until after the autumn break (March–April), when the weaners are put into these pastures.

Intensive grazing means using 2½–3 times the normal stocking rate for no longer than 30 days after each of the summer drenches are given. After the intensive grazing period, the paddocks are de-stocked to allow the pastures to re-grow. This means that the total stocking pressure for the ‘Smart grazed’ paddock will be the same as that for a paddock continuously stocked at the farms normal stocking rate.

The intensive grazing will reduce pasture residues to around 800–1000 kg DM/ha after the first summer drench, and around 600 kg DM/ha after the second. If there is insufficient feed, the periods of intensive grazing can be reduced. On the other hand, if there is excess feed the summer drenches can be ‘staggered’ for different mobs so as to provide a longer intensive grazing period or cattle can be used as well.

Finally, the weaners must be drenched with an effective drench before they start grazing the ‘Smart grazed’ paddock after the autumn break.

Smart grazing on a typical farm

A typical self-replacing flock of 5,000 DSEs in southern Australia is made up of 1,500 ewes, 1,500 wethers and 1,000 weaners, running at a winter stocking rate of 15 DSE/ha.

70 ha of ‘Smart grazed’ paddocks must therefore be prepared for the weaners. Thus, 2600 DSE (70 x 15 x 2.5) are needed to stock the 70 ha at 2½ times the normal stocking rate for each of the two intensive grazing periods— this uses all of the wethers and 70% of the ewes on the farm.

A timetable for ‘Smart grazing’

OCTOBER: Select the ‘Smart grazing’ paddock—choose one with a history of good winter pasture.

NOVEMBER: Give the first summer drench (this must be an effective product), then intensively graze the paddock at 2½–3 times the normal stocking rate.

DECEMBER: Remove the sheep to another part of the farm after 30 days intensive grazing. Ideally, the pasture residue should be 800–1000 kg DM/ha (2–3 cm in height).

JANUARY: Paddock remains unstocked until the second summer drench.

FEBRUARY: Give the second summer drench, then intensively graze the ‘Smart grazing’ paddock with the drenched sheep (again, not for greater than 30 days).

MARCH: Paddock remains de-stocked until the autumn break.

AUTUMN BREAK (MARCH–APRIL): Drench weaners and set-stock on the ‘Smart grazing’ paddock when pasture is greater than 600 kg DM/ha (1.5 cm). Weaners can remain there until spring but monitor their worm egg counts every 4–6 weeks.

Why does smart grazing work?

The intensive grazing periods

  • reduce the amount of pasture dry matter, making the pasture less suitable for the survival of worm larvae
  • ensure that there is no deposition of worm eggs on the pasture from the time of the first summer drench until the autumn break
  • probably allow the drenched sheep to ‘vacuum’ up infective larvae in much the same way as cattle do when they are used in alternate grazing programs with sheep
  • have the same cumulative stocking pressure from November to March as set-stocked paddocks grazed continuously by wethers
  • are quite flexible, what must not be changed is the need (i) not to exceed 30 days grazing after each summer drench, and (ii) for a fully-effective product to be used at the summer drenches

What are the benefits?

Results from a controlled experiment over 2 years in western Victoria show that, compared to weaners grazing paddocks prepared the usual way (grazed by wethers over the summer/early autumn), weaners grazing ‘Smart grazing’ plots

  • grew 13% more clean wool (2.29 vs. 2.03 kg) which was 3.5% broader (17.1µ vs. 16.5µ)
  • were 3 kg heavier in October (46.5 vs. 43.2 kg).

During winter, the egg counts from the ‘Smart grazed’ weaners didn’t go higher than 250 epg, a trigger for drenching weaners used by many farmers and their advisers. In contrast, the weaners on the paddocks prepared by set-stocked wethers exceeded 400 epg in both years.

The numbers of worm larvae on the ‘Smart grazed’ pastures in winter were from one-half to a one-third of those on pastures in paddocks prepared by grazing with set-stocked wethers.

Source: The epidemiology and control of gastrointestinal parasites of sheep in Australia. Edited by A.D. Donald, W.H Southcott and J.K. Dineen, Division of Animal Health, CSIRO 1978
Figure 3. The availability of infective larvae of the winter scour worms on pasture, showing a peak around June–August (depending upon the timing of the autumn break).

Drench groups and actives

Drench groups and actives Worms Examples* of brand names/comments
BZ or benzimidazole group (‘white’)B albendazole
barber’s pole worm, ‘scour worms’, adult liver fluke, nodule worm, aids control of intestinal tapeworm (Moniezia) Valbazen (albendazole)
WSD Fenbendazole (fenbendazole)
Oxfen (oxfendazole)
LV or levamisole group (‘clear’)B levamisole barber’s pole worm, ‘scour worms’, nodule worm Nilverm, Levamisole Gold (levamisole)
ML or macrocyclic lactone groupB (sometimes called ‘mectins’)
barber’s pole worm, ‘scour worms’, nodule worm Ivomec, Noromectin (ivermectin) Absolute, Vetmec, Paramectin (abamectin) Cydectin (moxidectin)
AD or amino-acetonitrile derivative groupB
barber’s pole worm, ‘scour worms’ Zolvix
SI or spiroindole groupM
barber’s pole worm, ‘scour worms’, nodule worm Derquantel is only found in a combination: Startect (abamectin + derquantel)B
OP or organophosphate groupM naphthalophos (NAP)
(OPs have lower or variable efficacy against ‘scour worms’ in the upper GIT and immature barber’s pole worm)
barber’s pole worm, ‘scour worms’ Rametin (naphthalophos is commonly used in combinations)
TZ or benzimidazole group (flukicide)N triclabendazole Liver fluke (all stages); not effective against round worms Tremacide
SA or salicylanilides/phenols groupN
Liver fluke (> 9 weeks and adult) and barber’s pole worm
Liver fluke (adults) and tapeworm
Closicare (closantel)
Oxyclozanide is only found in a combination: Nilzan (levamisole + oxyclozanide)B
IQ or isoquinolone groupN
Intestinal tapeworm (Moniezia) PraziquantelN is only available in combination with broad-spectrum drenches. First DrenchB, Genesis TapeB
*ParaBoss does not endorse specific brands, these are presented here as examples only.

Breadth of activity across different worm species: BBroad-spectrum; MMid-spectrum; NNarrow-spectrum

Actives: An ‘active’ is the chemical in a drench responsible for killing worms. Some drenches have more than one active and are called ‘multi-active’ or ‘combination’ drenches.

Combination or multi-active treatments: Proprietary treatments containing more than one active. Formulated to be compatible as a mixture. Note: Do not mix your own drenches unless the labels state that you can.

Product formulation: All single actives are available as oral drenches. Moxidectin is also available in injectable products. Intra-ruminal/controlled release capsules are available with BZ and/or ML actives. Abamectin is also in a pour-on formulation for both lice and worm control.

Length of protection: Varies from short-acting (‘knock-down’ that kills susceptible worms within the animal) to mid- length (1–4 weeks) and long-acting (approx. 3 months), which not only kill susceptible worms already in the animals, but also susceptible infective larvae that the sheep eat during the protection period.

‘Scourworms’: Mainly black scour worm and (small) brown stomach worm, but also others.

Label: Check product labels for full details. Follow the label.

Other parasites: The Drench Decision Guides show effectiveness of groups against other parasites of minor importance.

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