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South Australia worm update - November 2012

Colin Trengove, Sheep Health Lecturer, Uni Adelaide (colin.trengove@adelaide.edu.au)

A dry finish to spring has resulted in suboptimal pasture growth as well as restricted opportunity for worm larval survival on pasture. Worm counts have been relatively low over the last month limiting the need for drenching. Worm egg counts are of even greater value in these circumstances, as they will often indicate no need for a drench. There is no point in dosing sheep with chemical where there are low worm numbers as these mild burdens can actually be beneficial in maintaining a stimulus to the immune system. Even weaners have hopefully received an effective drench at weaning and may not require a drench going into summer.

If there are low worm burdens going into summer and the preceding low rainfall pattern continues, repeat worm egg counts can be delayed until February to assess whether a drench is required before autumn. However, any rainfall in excess of 20 mm, especially combined with cooler weather, can soon change this scenario. A worm egg count is recommended 3 weeks after a significant summer rain to assess whether there has been subsequent worm larval emergence and new worm burdens established.

The advantage of regular monitoring is that you can often save on drench and never need to second guess. This is especially important if your flock is at risk to Haemonchus spp or ‘barber’s pole worm’ during summer.