Redefining the summer drench requirements in Mediterranean climates to slow the development of parasite resistance

Research need

The traditional summer drench programme, in Western Australia, has provided excellent worm control but there remains little doubt that it has been a key contributor to the severity of drench resistance.

Key research questions

Is it possible to devise new summer drenching programmes that reduce selection for drench resistance but still provide good worm control?

Methods

The research is based on results, collected over the last few years from several demonstration farms throughout southern WA, that it might be possible to avoid summer drenching of mature ewes on some farms in some years.

The productive effects of not providing the first summer drench have been estimated in mature ewes by comparing growth and wool production when receiving at the start of summer either:

• Nil drench
• Standard first summer drench
• Controlled release capsule

Conclusions

Mature sheep should receive the traditional first summer drench ONLY if worm egg counts exceed 200 epg.  The production penalty of withholding the first summer drench will generally be very small.

Recheck worm egg counts of mature ewes no later than first week of April and treat ONLY if worm egg counts exceed 200 epg.

Personnel

Dr Rob Woodgate
Veterinary Officer
Department of Agriculture & Food, Western Australia

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