Back to State Outlooks

South Australia worms, flies and lice update - August 2018

SA WormBoss Worm Control Programs

SA WormBoss Drench Decision Guides





Adelaide: Colin Trengove, Sheep Health Lecturer (UA Roseworthy campus) (

What impact have recent weather conditions had on sheep parasites? The answer is, not much as recent monitoring indicates an abundance of worms despite minimal ground cover in most agricultural areas.

Recent rainfall has been quite variable north of Keith and total rainfall for the 8 months to mid-August are in the order of 10–35% of long-term averages across most of the state. The upper Eyre Peninsula, upper North and Riverland are experiencing the leanest conditions. The south east is more fortunate enjoying a more normal winter with rainfall in the 40–80 percentile band.

The long dry start to the year would be expected to “clean up” pastures and limit worm burdens, but recent monitoring around South Australia indicates about half of the mobs tested have needed a drench based on a 200 eggs per gram cut-off. This is not surprising as while moisture has been scarce this year so has UV light and the thick cuticle (skin) of worm larvae enables them to survive with scant protection as long as they are not being scorched by the sun. Even Haemonchus contortus (barber’s pole worm) larvae survive the many frosts already experienced, but the cold will prevent new eggs from hatching to larvae.

Similarly flies can’t cope with cold winter conditions, but lice delight in the microclimate close to the warm skin of sheep and away from the sunlight. Many recent detections of lice in markets including in shedding sheep has prompted PIRSA to run a lice detection and treatment information day at Mount Pleasant sale yards on 24 August.

Worm egg count monitoring tends to be minimal during mid-winter as most ewes are drenched prior to lambing regardless of their worm burden. However, the recent surge in monitoring has been in lactating ewes and the significant proportion that require drenching indicates the extended contamination of pasture since lambing. Monitoring in the south east has also revealed high counts in weaner lambs (up to 10,000 worm eggs per gram of faeces).

Lambs rarely need a drench at marking, as their exposure to worm larvae is minimal up to 6–8 weeks of age, but drought years can be an exception. Checking worm burdens in lambs requires them to be separated from their mothers for 15 minutes in a clean pen to ensure that only lamb dung is sampled. While this may be an inconvenience it can be an added insurance against worm concerns prior to weaning. If lambs do need a drench, the general recommendation is to use at least a double and preferably a triple active drench i.e. one that has two or three chemical ingredients to optimise efficacy and minimise the development of drench resistance.

There have been many reports of ewes and lambs lost this year in the lead up to lambing and the first few weeks of lactation. This has no doubt been due to the energy in feed not meeting the demands of late pregnancy and lactation. In addition, low protein intake lowers immune status rendering ewes and lambs more susceptible to worms, bacterial infection and other parasites. Monitoring ewe worm egg counts and condition score periodically during pregnancy will provide opportunities for critical management decisions before losses are experienced.

If ewes are in poor condition, early weaning should be considered, but lambs need to be at least 8 weeks old for their rumen to be sufficiently developed. Do a worm egg count and decide upon the most effective drench to use. Move weaners to a low worm risk paddock to ensure that they can grow at an optimal rate without the handicap of a developing worm burden. Feed quality will not be a concern once green feed is available, but weaners need a dense pasture at least 4 cm high to optimise growth i.e. covering the heel of your boot and equivalent to 1200 kg Dry Matter/Hectare.

[Editor’s note: The percentile rank / band of a score is the percentage of scores in its frequency distribution that are equal to or lower than it. In this case, a percentile band of 40 indicates that 40% of the rainfall scores are lower than it.]

For August 2018 state outlooks, please follow the links below:
Back to State Outlooks