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South Australia worm update - February 2012

Colin Trengove, Sheep Health Lecturer, UA Roseworthy campus:

February has settled into a more typical month with scant rainfall around the state and temps hovering in the 30's for a few days at a time. Some areas in the mid and lower north are still grazing off crop/pasture regrowth after rain earlier in the month, while the south east is desperately short of feed following a dry spring and summer.

Egg counts have generally been unremarkable, but those areas that have received significant rainfall during summer need to be monitoring closely for residual worm contamination and pickup. A drench should be considered where egg counts are above 100 eggs per gram in summer, but also taking into account sheep age, condition score and future grazing. Ewes coming off stubbles have generally been in good condition (ie above score 3) and so a worm drench may not be warranted depending on what future grazing and supplementary feeding is install for them.

Other major considerations in the decision whether to given a (second?) summer drench are:

  • the desire to minimise pasture contamination going into autumn and the season break ie the earlier in the season a drench is given, the longer the pasture decontamination phase assuming the pasture is left unstocked between the drench and the autumn break; and
  • the intent to minimise drench resistance and so avoid using the same drench group in consecutive drenches during summer e.g. if Ivermectin was used for the (first) summer drench in November/December it is highly undesirable to use it again in February/March as this is considered 10 times more likely to contribute to the development of drench resistance.

Several mobs should be egg counted during February to determine whether drenching is indicated to both optimise the use of diminishing feed reserves and lessen the carryover of worms into the following winter. A strategic drench now can minimise the need for drenching over the remainder of the year, but is also best avoided due to the ever present threat of drench resistance.

For February 2012 state outlooks, please follow the links below:
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