Victoria worms, flies and lice update - November 2015

Hamilton: Andrew Whale, Livestock Logic (a.whale@livestocklogic.com.au)

Don’t select for drench resistance during the drought!

Conditions in the south west of Victoria remain dry with plenty of lambs now going onto full grain rations for finishing. Dry standing feed levels are well below normal years (similar to 12 months ago) and we would expect the majority of producers to be feeding large numbers of stock by January.

Drought conditions do have some benefits from a worm management perspective. The lack of carryover feed means that it is a good opportunity to clean your paddocks of worm levels prior to autumn. But it is also an opportunity to heavily select for worm resistance with unnecessary drenching, so we need to make the correct decisions on whether to drench, how many to drench and what product to use.

Do I Need to Drench

• Based on Worm Egg Counts (WEC). Where counts aren’t reducing production then there are advantages to delaying the drench a few more weeks (particularly where it is still green).
• Use lower drench trigger levels in summer, as we are concerned with both pasture contamination levels and production loss.

Leave a Proportion of the Mob Un-drenched

• Unless drenching lambs, skinny sheep (<CS2.5) and/or sheep with egg counts greater than 500 epg, leave the fattest 5­–15% of sheep un-drenched. This leaves a proportion of the worms not exposed to a drench, thus reducing selection pressure against worms.

Get the Right Drench

• Must avoid any long-acting products over summer—capsules or moxidectin.
• Use highly effective drenches—new actives or 3-way combinations.

Post-drought we can often see the emergence of drench resistance on properties that have previously had effective drenches. This is due to overzealous drenching in the summer when larvae levels on pasture are very low. Ensure that the drench is required this summer before selecting for drench resistance.