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Western Australia worms, flies and lice update - September 2017

WA WormBoss Worm Control Programs

WA WormBoss Drench Decision Guides





Albany: Brown Besier, Brown Besier Parasitology (

Across the state...

There’s a lot happening with sheep in springtime, when pasture nutrition is normally at its best—prime lambs rapidly gaining weight before turn-off, ewes getting back into condition ahead of mating, and shearing in many flocks. It’s also a prime-time for parasites of all kinds, as conditions warm up and there is still rainfall and plenty of pasture moisture—think worms and blowflies, and in some cases, coccidiosis in lambs. And if shearing is due or just happened, think body lice treatments.

The very poor season has added some complications, not least that in most districts sheep are generally in lighter condition than usual, and pasture is far tighter. Lower ewe condition scores and lower lamb growth rates means less resistance and tolerance to worms, and a higher chance of worm intake as they are forced to graze lower to the ground. Worm control will have to be especially good this springtime to avoid significant losses to parasites. Some key points:

Lambs usually need a drench in spring

A drench by 14–16 weeks of age is almost always necessary. This is the most worm-susceptible time of a sheep’s life, and for most it’s at a time of year particularly favourable for worms.

A drench at this time is commonly given to Merinos at weaning, but prime lambs also need effective worm control. Leaving it beyond about 16 weeks risks severe worm effects, unless a Worm Egg Count (WEC) shows counts are low.  Recent MLA-supported studies in WA show that by 14 weeks, even moderate worm burdens (counts above 250 eggs per gram) can reduce prime lamb growth rates, unless they are growing rapidly (above 240 gm/head/day over the last couple of months).

Action: Either drench lambs at 14–16 weeks of age as a routine, or do counts before 14 weeks to check the necessity.  The latter may pay if there are grounds to believe counts will be low: either due to high growth rates (check this—they are often over-estimated), or if worm control in the ewes was planned so lambs would be faced with a low worm challenge (pre-lamb treatments and moving to low-worm pastures).

Check worm counts in ewes

In most years, there is usually no need to drench ewes when the lambs are weaned, as with the lambs off them their worm immunity will have returned to its highest level and they generally gain weight rapidly with good spring nutrition.

However, in poor pasture years the worm resistance and resilience (ability to tolerate worms) of ewes can be severely reduced. There have been some cases of heavy worm burdens in ewes following lambing, and scouring seen at lamb marking. In this case, a drench then is indicated.

Obviously this is not really feasible where worms are suspected in ewes immediately after the marking event (especially if mulesed), but a worm egg count  can be taken from the paddock to show what is happening (check that ewe dung pellets are selected). If counts are high and the ewes are in poor condition, a drench is needed as soon as it is possible to yard them. If counts are low and no drench is needed, early weaning of the lambs can be considered, to give the ewes as much time as possible to regain their weight.

A word on coccidiosis

Coccidia are single-celled organisms (protozoa) that infect the lining cells of the gut, and are transmitted via the pasture as for worms. They usually pass unnoticed, but in very large numbers they can cause severe damage resulting in scouring and in some cases, deaths—this is then called “coccidiosis”.

In the Australian sheep industry, we see coccidiosis mostly in very young lambs in poor seasons, when nutrition for ewes and lambs is poor and the lambs are forced to graze early and close to the ground. The disease occurs mainly in lambs less than 3 months of age, as after this they gain a good immunity to coccidia. However, if lambs are seen to be scouring before marking, coccidiosis should be suspected as it is too early to be due to worms. 

Cases of coccidiosis have been diagnosed in WA this year, which is not a surprise given the pasture situation. There is no over the counter treatment, but your veterinarian can prescribe and supply suitable products, including one that can be given as a single drench where affected lambs can be singled out. Moving the mob—ewes and lambs—onto any other pasture may help, as there will be a lower intake of coccidia than where an outbreak has occurred. The longer term cure is to ensure good nutrition to the lambs and ewes, although this is obviously more easily said than done in a hard season. If suspected, it is worth consulting a veterinarian or adviser, especially where scouring involves lambs over 3 months, where it is almost always due to worms.

Time for drench resistance testing

A stocktake on the drench resistance situation every couple of years is very worthwhile. Resistance has developed on some farms to all except the newest drench types, and it’s important that only fully-effective drenches are used for any treatment in summer or autumn.

As mentioned in earlier newsletters, there are 2 main ways to do about this:

  • A full drench resistance test: this remains the gold standard. Small groups of lambs are dosed with different drenches and their worm egg counts after treatment compared with an undrenched control group.
  • A quick check of drenches: taking worm egg counts before and after a mob is treated, to show the percentage reduction in counts. It simply involves collecting samples when a mob is in the yards for drenching and then from the paddock, 2 weeks later. Over a number of drenching occasions, several drenches can be checked.

Lambs between 4 and 6 months of age are ideal for this, as they generally have significant worm egg counts at weaning, or within a few weeks before a drench. It’s best to talk to an adviser or to check the WormBoss website, to make sure that the correct procedure is followed.

Flystrike management

As a follow-up to the newsletter comment last month, flystrikes have started or will soon do so across the state. Depending on what pre-planned management measures have been taken to reduce the attraction of flies to sheep in the short term (such as shearing, crutching and worm control), the main decisions are the need for either whole-flock preventative treatment or treatments to affected mobs or individuals as strikes occur.

The FlyBoss website has some user-friendly tools to help with these decisions, and full information on the chemical options. The new DPIRD phone app, FlyStrike Assist, also has information on protection and withholding periods. Entering the proposed treatment date shows when these periods will end, making it easy to choose between options. 

Lice control

Shearing will be on the agenda for many farms at this time of year, and with it comes decisions on treatments for lice. If any lice have been seen—directly or by signs in the fleece—off-shears treatment is necessary, and that means a decision on whether by pour-on or dipping (and what type of dip), and the product to be used. There are a number of effective treatment options, but remember that resistance by lice to the insect growth regulator (IGR) and synthetic pyrethroid (SP) classes is common, and these now have little role for lice eradication. The LiceBoss website has much useful information and innovative decision tools to help sort out the best way to go.


Esperance: Nicole Swan, Swan’s Veterinary Services (

Spring has sprung and with good soil moisture and sunshine the pastures are getting going. Unfortunately, this weather is also ideal for any worm larvae that may be developing on pasture. 

Weaning is imminent and it is essential that weaners receive an effective drench at this time. Although faecal worm egg counts may be low prior to weaning, this is a stressful time for young sheep and low burdens can still have an impact. Ideally, weaners will be drenched onto a clean pasture. For a paddock to be clean at this time of year it must not have had any sheep on it for at least 6 months.

If your property is in a barber’s pole area then using a drench that provides residual protection is recommended.

If you still have undrenched weaners and you have not conducted a Drench Resistance Test in the last 2 years then it is strongly recommended that you contact your veterinarian prior to any drenching to organise to do this. You will need between 90 and 120 undrenched weaners with a scour worm burden of 300 epg or more.


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