Colin Trengove, Sheep Health Lecturer, UA Roseworthy (firstname.lastname@example.org)
What a summer - after many days in which you could fry an egg on your bonnet and worms in the paddock, the recent 30-100mm rainfall has definitely been sufficient to promote worm larval emergence. What are the risks? These conditions are ideal especially for Haemonchus (Barbers pole worm) to emerge in susceptible areas and so producers need to be vigilant in monitoring for the presence of this worm in the following 3-4 weeks.
The dry hot summer up to mid February had promoted low worm risk pastures reflected in lower egg counts generally, but significant summer rainfall not only reduces dry standing feed value, but gives worms the signal to resume their life cycle. Their survival on the ground like the green feed that germinates is likely to be short lived as hot dry conditions would be expected to return in February/March. However, the short term green feed provides a great protein boot to grazing livestock and the brief access to worm larvae can be sufficient to create significant worm burdens going into autumn and beyond. The logical strategy is to monitor for worm larval intake by WEC monitoring 3-6 weeks after rainfall exceeding 30mm.
A "second summer drench” is ideally avoided from a drench resistance perspective, but strategically the need is best based on the monitoring results. Remember – if a drench is deemed necessary in late summer, use a drench group that you haven’t used in your flock in the past 12 months.