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South Australia worm update - May 2013

Colin Trengove, Sheep Health Lecturer, UA Roseworthy (

Steady soaking rains across SA over the past 3 weeks has ensured a timely break to the season and soil temperatures still in the 'mid teens' has promoted prompt germination and growth of perennials and annuals alike. Little runoff has occurred due to the steady nature of the rainfall and the parched state of the soil after a long dry since last spring.

Worm larvae will be just 'hitting their straps' three weeks in to the green season and so sheep will be loading up on meat meal as they graze close to the ground on the green carpet. Worm egg counts have been relatively low in late autumn due to the exceptionally dry summer and autumn leaving minimal worm contamination. However, the autumn break always makes way for a new worm population and so stock owners need to be vigilant at this time of year.

Pre-lambing monitoring will have determined the need for a drench and so the situation will not change if minimal worm burdens coincide with low pasture contamination. The biggest risk is for ewes not monitored and not drenched or where stock are moved around to utilise the short feed and pick up the newly emerged worm larvae in the process.

Once lambing has started little can be done about ewe worm burdens until marking and even then they will have contaminated the lambing paddock to in turn burden the lambs as they start to graze. An early weaning drench would be prudent in this situation.

For those lambing in June/July it would be timely to monitor WECs now to assess the need for a pre-lambing drench, but bearing in mind that it will take 3-6 weeks after the autumn break for larval worm contamination to result in significant counts of worm eggs in the sheep faeces. 

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