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South Australia worm update - August 2012

Colin Trengove, Sheep Health Lecturer, UA Roseworthy campus:

Late winter rains have raised the hopes of croppers and graziers alike for a good spring to finish the season. Worm burdens have generally been modest but sufficient to indicate that a weaning drench is essential.

It has been a relatively tough year with a late break and limited pasture growth during winter. As a consequence ewe lactation and lamb growth has been reliant on restricted feed on offer plus supplements where available. The harsh start to lambing meant that pre-lambing drenching was common place and so limiting winter worm contamination.

Weaning is a good time to do a drench resistance trial if worm egg counts are sufficiently high (i.e. over 250epg). Multiple drench resistance is widespread leading to suboptimal worm kill when various drenches are used. The specific drenches which fail to be effective will vary with every farm. A trial to determine which drenches are effective in your flock should be done every 2-3 years as the situation can change relatively quickly depending on your drench use, management practices and environmental conditions. Your animal health consultant can best advise on how to undertake this if any queries.

Sufficient moisture combined with rising soil temperatures and associated mineralisation will promote the spring flush of feed. The improved nutrition as a result of more feed of better quality in spring boosts the immune system and helps to suppress developing worm burdens. However, it does not impact the existing worm population in the gut and so monitoring +/- drenching is still important to ensure that sheep in poor condition are not hampered in their recovery as better feed becomes available.


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