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New South Wales worms, flies and lice update - November 2020

NSW WormBoss Worm Control Programs

NSW WormBoss Drench Decision Guides






Central West LLS

Condobolin: Hanna Thomas, DV (

Although the majority of WormTests conducted in the Condobolin area have indicated low worm burdens, recent investigations have found increasing levels of barber’s pole worm. This is despite the fact that the stock in question were drenched the month prior, emphasising the need to manage drench resistance and know which drenches are effective on your property. It is recommended that producers conduct a DrenchTest every 2–3 years to determine the level of resistance present to various drenches on their property. Another way to test drench effectiveness is a DrenchCheck; this involves doing a WormTest up to 10 days prior to drenching, then conducting another WormTest 14 days after drenching. This will allow you to gauge if the drench has been effective.

Coonabarabran: Kate Atkinson, DV (

Flystrike remains an issue as we head into the warmer months with a high average monthly rainfall. Using flystrike chemicals strategically will help slow resistance to products and increase the longevity of their effectiveness.

Like drenches, rotating chemical groups for flystrike treatments will help slow resistance development. Be aware that cyromazine products (such as Vetrazin™) and dicyclanil products (Clik™) are in the same chemical group (Insect growth regulators). Organophosphates have widespread resistance and also present human health implications, so should no longer be used.

Minimising the need for chemical use can be achieved by selecting genetically for flystrike resistant sheep, docking tails to the correct length (to the tip of the vulva in ewes) and shearing/crutching strategically during the high risk period. Strategic shearing and crutching can give up to six weeks’ protection.

If a long acting flystrike prevention is used at the start of the high risk period, shearing (body application) or crutching (breech application) are useful at the end of the risk period, as this is when the concentration of the product declines to below effective level, creating the greatest risk period for resistance issues. Alternatively, a short acting product application (from a different chemical group) at this time can act as a ‘tail cutter’ for the first product.

Coonamble: Jillian Kelly, DV (

The Coonamble district is experiencing a bumper harvest, with headers and road trains going 24/7. It is easy in such a busy time to forget about your stock, but it is really important to keep an eye on their worm burdens and flystrike. Worm egg counts continue to be high on some farms, the highest individual count to date being a whopping 10,000 eggs per gram! Many producers don't have clean paddocks and so are having to rely on long-acting drenches, which is an issue with so few on the market. Resistance by barber’s pole worms to moxidectin is also extremely common, potentially shortening the length of protection. We are still trying to get as many farms as possible to do a DrenchTest to fully assess their level of drench resistance and to make better drenching choices in years to come.

Flystrike is a big issue at the moment. Many producers are finding that chemical preventatives are not working or are not lasting as long as the label states. This is not surprising given the level of resistance found during the Department of Primary Industries’ testing of maggots over the past few years. We strongly urge producers to think more holistically about their fly management and not just rely on chemicals. Sheep may need to be shorn or crutched more frequently. Low risk sheep (i.e. freshly shorn sheep) should be prioritised into high risk paddocks (e.g. paddocks with long, wet grass) and vice versa.

Any struck sheep must be identified and treated with an appropriate fly treatment. A good way kill maggots is by putting the wool and maggots in a black plastic bag and leaving it in the sun. If you fail to kill all the maggots on the sheep, the resistant maggots live and breed on!

In cattle, small black fly burdens are causing pink eye. We are yet to see buffalo fly in our district but are asking producers to keep a close eye out as summer progresses.

Forbes: Nik Cronin, DV (

Harvest is in full swing, so there will soon be stubble paddocks available for grazing stock. This is considered a great time for strategic drenching — maybe to coincide with weaning, or at least with the first summer drench — as an ungrazed stubble paddock should be free of worm larval contamination.

In general, lambs should be drenched at weaning, as this is the age when they are most susceptible to worm burdens. An effective drench given to weaners going on to a clean paddock will give them the best start to getting through summer.

However, for dry, adult sheep it is recommended to conduct a WormTest first, because if the egg count is low then a drench may not be required. Drenching sheep unnecessarily creates another opportunity for drench-resistant worms to survive. Particularly when conditions are drying off and there are few worm larvae on the paddock, these survivors in the sheep can then go on to become the dominant worm population on a property once the season breaks in autumn, which fast-tracks drench resistance. The key is to conduct a WormTest first, and don’t drench if the egg count is below 100 eggs per gram. Then continue using WormTests to monitor egg counts in these undrenched mobs over summer.

Another strategy to delay the development of drench resistance is to leave a small percentage of the mob undrenched. These sheep will carry through unselected worms to dilute the resistant worms that survive the drench. This is not a good idea if barber’s pole worm is present, so request larval typing on your worm test to ensure this is not the case.

After using a drench, it is good practice to test its effectiveness by repeating a WormTest 10-14 days later. WormTest kits can be found in all our Central West Local Land Services offices.

Nyngan: Kelly Wood (

We have been seeing a real variety in worm egg counts (WECs) around the Nyngan district with a number of WormTests recording 4,000–5,000 eggs per gram (epg). These are likely to be barber’s pole worm, bringing an imminent risk of deaths, but if they also contain high proportions of scour worms the sheep would also be losing production.

With such a good season and strong prices at the sales, it’s a shame to be growing worms rather than sheep. So, how wormy are your sheep, what types of worms are they carrying? Without conducting a WormTest, you just don’t know. Larval cultures are strongly recommended to give a species breakdown, as your drenching thresholds would vary depending on the worm species.

Some of the high WECs we have seen have been in weaners that have been recently drenched and moved to clean pasture. Unfortunately, this means that not only does new drench have to be purchased and the mob re-mustered, but the weaner paddocks have also now be contaminated with large larval burdens of worms that are likely resistant to the drench used. These cases really highlight how important it is to undertake a DrenchTest to test for resistance on your property every 3–5 years ensuing you are using the most effective drenches you can.

If you have weaners you haven’t drenched yet and are interested, get in touch with your local district vet to discuss conducting a DrenchTest on your farm. If you haven’t done one in a while and you’re not sure how effective the drenches you are using are, you should do a WormTest just before drenching. Repeat another WormTest exactly 14 days after drenching and include larval cultures. If your epg at this time is greater than 100, it is likely there is resistance and you will need to consider other products, particularly combinations. Your local district vet can help you plan a drenching strategy to get your sheep through this wet season and the region-specific Drenching Decision Guides on the WormBoss website are full of useful information relevant to your area.

With the wet weather we are also seeing lots of flystrike, particularly body strike. Checking your sheep regularly and appropriately treating struck sheep is important not only from a welfare and production standpoint, but also to manage the fly populations on your farm. We are recommending rotating chemical classes used to prevent strike (as you would after using a long-acting drench) to reduce the impact and development of resistance. We are also promoting integrated management with crutching, shearing and paddock selection in the short term. Strike is highly repeatable (a small number of sheep disproportionately contribute to the number of strikes each year) and you should consider culling for repeated strike as part of a wider genetic strategy for limiting the impact of flies.

Riverina LLS

Wagga Wagga: Dione Howard, DV (

The warm temperatures and spring showers have seen barber’s pole worm counts increase in sheep and goats across the area. Three WormTests from the last week around the Wagga area measured 3,700, 4,500 and 11,500 eggs per gram.

Barber’s pole worm causes death, anaemia, lethargy and collapse: all signs which have been seen in affected mobs in the area. Don’t wait until you see stock losing condition or sick. For all classes of sheep and goats, use regular WormTests to monitor worm burdens.

It is easy to grab samples for a WormTest during breaks in harvest; these results will assist you in making the best drench decisions.

Narrandera/Griffith: Sophie Hemley, DV (

With harvest well under way there have been relatively few WormTest submissions from the Western Riverina region. Three tests of note are:

  1. A mob of six-month-old Merino lambs in good body condition that were drenched in mid-July returned an average pooled worm count of 1,040 strongyle eggs per gram (epg). On culture 98% were Trichostrongylus sppy (black scour worm) and the remaining 2% were Teladorsagia spp (brown stomach worm). Interesting there were no signs of a worm burden in this mob.
  2. A producer noticed that a tail was slowly developing in a mob of eight-month-old Merino lambs. The lambs were losing condition but not scouring. The mob had no drench history. An average pooled worm count of 480 strongyle epg was returned (individual animals 0-1,200 epg). On culture 93% were Trichostrongylus spp (black scour worm) and the remaining 7% were Teladorsagia spp (brown stomach worm). All other counts (including fluke) were negligible.
  3. A mob of dry mature Merino ewes had been grazing the same pasture paddock for almost two months and returned a very low worm egg count.

This month there have been several producers asking for advice on quarantine drenches when introducing new sheep on farm. It is best practice to quarantine drench all oncoming sheep with a combination of no less than four unrelated drench actives, one of which should be a new active (monepantel or derquantel). For complete advice on quarantine drenching, you can either call your local District Vet or visit the WormBoss website.

Flystrike is continuing to be an issue in many flocks. For more information on how to solve you current flystrike problem, you can get in touch with your local District Vet or head over to the FlyBoss website.

Northern Tablelands LLS

Inverell: Andrew Biddle, DV (

Seasonally things have tightened up a bit here on the Northern Tablelands.

Barber’s pole worm waves and blow fly tsunamis have receded, but we would welcome the follow up rain.

Worm levels are generally low so keep monitoring.

The main issues currently are Clostridial disease and vaccine deficiency.

Western LLS

Buronga: Trent McCarthy, DV (

The season across large areas of the western district looks promising with some further rainfalls predicted. Some cases of black scour worm have been detected through WormTest results on some of the more intensively managed or irrigated country. Scours and ill-thrift was reported on a property in recently introduced sheep, that were purchased from interstate and that failed to respond to drenching. A quarantine drench is critical to avoid introduction of drench resistant worms to a property when the animals have an uncertain history. Quarantine drenches should consist of a least four different chemical classes, with at least one class being the newer drench class categories, such as monepantel (Zolvix™) or derquantel (Startect™). In this case Ovine Johne’s Disease was established as the causative agent; this is caused by bacteria that can cause chronic wasting and scours, generally in older animals. It is an important reminder to always ask for a national Sheep Health Declaration and check the details of purchased stock carefully.

Flies and flystrike activity have been on the rise due to recent moist and warm conditions. Producers are reminded to adopt an integrated approach to flystrike control; including genetic selection (reduced selection for traits such as wrinkle, dag, breech cover and fleece rot that increase flystrike risk), targeted management and husbandry timing (crutching or shearing around risk periods), and careful use of chemical control methods where indicated. Check out some of the resources on the FlyBoss website for more information and tools to assist your enterprise.

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