South Australia worms, flies and lice update - February 2018

SA WormBoss Worm Control Programs

SA WormBoss Drench Decision Guides





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

Typical hot dry January/February weather has augured well for worm larvae kill on pastures. However, the impact of the early summer rain in some parts of the state is still evident with reports of Haemonchus or barber’s pole worm infections in the Riverland and South East. While these reports are sporadic they have significant consequences due to the lethal impact of this blood sucking parasite.

Worm egg counts from Eyre Peninsula to the South East indicate variable worm burdens highlighting the need to assess worm risk (WormTest) in several mobs on each property in order to maintain effective worm control across flocks. Counts up to 1300 eggs per gram (epg) in dry crossbred ewes and 700 epg in crossbred lambs in the Adelaide Hills and South East respectively during the last 4 weeks demonstrate the value in frequent monitoring as significant production loss is occurring with these worm burdens. In contrast, many egg counts have been zero or less than 100 epg in animals of similar description and removing  the need for a summer drench. Summer drenching is discouraged as it is more likely to encourage the development of drench resistance. However, monitoring worm egg counts is paramount in decision making on the need for strategic drenching.

The recent trend in marketing double or triple active drenches is aimed at prolonging the life of the chemicals in these products. It represents a subtle change in the management of drench resistance where the emphasis is on limiting worm survival by the use of two or more chemicals at each drench rather than periodically changing the type of single chemical used during the year.

Inclusion of trace elements in drench such as selenium or cobalt is sometimes queried as to the benefit of this practice. It is sometimes difficult to purchase a drench or vaccine without trace elements. The important consideration is to be careful that the same trace elements are not being provided simultaneously by alternate routes. This is especially the case with selenium and copper where dosing with two or more times the recommended intake can cause sudden death or severe ill-health. The dose of trace elements in drench or vaccine is relatively small, but ensure the same minerals are not being provided in other oral or injectable forms around the same time.

Another consideration is that trace elements are most likely to be lacking during winter/early spring, as young grass has limited ability to accumulate minerals from the soil. And so the highest need for trace elements is during this time of the year and not late spring/summer when worm drenching is more likely to be carried out.