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South Australia worms, flies and lice update - November 2015

SA WormBoss Worm Control Programs

SA WormBoss Drench Decision Guides


November has been milder than October and remained mostly dry. An exception was a high pressure system that brought a sudden 30-100mm rain across Eyre Peninsula and mid and upper north mid month. Conditions dried quickly and so caused only minor disruption to harvest. Similarly, the rainfall is unlikely to have significantly changed the worm risk to livestock due to the rapid drying out.

Recent worm counts indicate low worm burdens in sheep in the mid north through to the Adelaide hills and mallee with the exception of some lactating ewes and weaners with counts high enough to warrant a drench. This highlights the opportunistic nature of worms that capitalize on animals with compromised immunity such as late pregnant through to lactating ewes. Similarly, young animals up to hogget stage are more susceptible to worm burdens because they are still acquiring immunity through repeated or sustained exposure to worms.

It is recommended that worm burdens be assessed in late spring as pastures hay off to determine the need to eliminate significant worm burdens going into summer. However it is also recommended that drenching only be undertaken if there is a demonstrated necessity i.e. egg count > 100 epg (although this cut off will vary with location, aversion to risk and local advice). To reduce the risk of developing drench resistance it is preferable not to drench going into summer, or if deemed necessary, refugia needs to be encouraged i.e. survival of worms that are not exposed to drench chemicals. One method to achieve this is by leaving 10-20% of the mob in better body condition undrenched on the basis that these animals are less likely to have significant worm burdens. As a general rule the nutritional status of animals in condition score 3 or better will ensure they maintain low worm burdens regardless of the risk of exposure.

Regardless of seasonal conditions remember to monitor worm burdens in young animals every 1-2 months as they can establish worm burdens rapidly due to their low immunity. Here's wishing you a worm free festive season!