Appendices: Further Information on Sheep Worm Control for Victorian Winter Rainfall Regions

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.

Prevention

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).

Detection

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 twice a year (late summer and winter) for at least two years (i.e. 4 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 testing times are not always positive, then continue testing at the specified times to decide whether to drench.

If all 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 host snails are not present on your property to transmit 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 (EMAI) at Menangle. Also, a faecal antigen test for fluke is available through EMAI and Charles Sturt University’s Veterinary Diagnostic Laboratory.

Response

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, routine treatments for liver fluke should be given to sheep that have been grazing the affected paddocks in:

• February–March (at or after the second summer drench, but before a secondary snail breeding season in autumn)
• July–August (winter—before the main breeding season of the host snail which occurs in spring)

An important alternate strategy, where only a small portion of the farm is affected, is treatment either onto (before grazing) or off (after grazing) the affected paddock(s), or both.

Some treatments for roundworms (scour worms and barber’s pole worm) 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 winter 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 February– March, this treatment should be a flukicide other than triclabendazole (if this was used in winter). This treatment rotation will reduce the rate of development of fluke resistant to triclabendazole.

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.

Table 1. Fluke treatments and the age of fluke from which they are effective

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 winter 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 95%.

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

The following table applies mainly to brown stomach worm (Teladorsagia circumcincta), black scour worm (Trichostrongylus species) and barber’s pole worm (Haemonchus contortus).

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

Introduction

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 ‘Smart grazing’

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.

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 infective larvae that the sheep eat during the protection period.

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

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

Other parasites: Drench groups and actives shows effectiveness of groups against other parasites of minor importance.

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