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Western Australia worms, flies and lice update - June 2018

Albany: Brown Besier, Brown Besier Parasitology (brown@bbpara.com.au)

WA Worm outlook

We finally seem to be into winter, but with quite variable pasture growth around the state. Sheep nutrition has a lot to do with how well they handle worms, but the winter worm pattern has well and truly started even if pastures are short.

It must now be assumed that sheep will be exposed to worms in most paddocks, except those occupied by sheep that have low or zero worm egg counts over previous months. As that’s not easy to gauge, it’s time to start regular monitoring of worm egg counts to check how worm burdens are running.

The main seasonal issues at present concern lambing ewes, and last-year’s lambs.

Lactating ewes:  a drench at lamb marking is probably warranted if a significant proportion (say, more than 20%) are actively scouring. This indicates that their milking ability may be reduced, and that a lot of worm eggs are going onto the pasture. This is likely to lead to significant worm burdens in the lambs as they start to graze, with consequences for their growth rates.

If the ewes look to be in acceptable condition with no significant scouring, they generally won’t need a drench at this time. Ewes given a long-acting drench prior to lambing will not need further treatment.

Lambs at marking: There should be no need for a drench on the marking cradle to the lambs.  We don’t often see significant worm counts until they are 10 or more weeks of age, and usually the first drench can wait until weaning (or 14–16 weeks, whichever comes first). 

Pre-lamb ewes: if yet to lamb, the main issue is whether they have worm burdens likely to lead to problems while lactating. Check counts 2­–3 weeks out from lambing, and drench if higher than 100 eggs per gram. This is a very low figure, but as ewes spontaneously lose their worm immunity for a few weeks at and after lambing, there is the potential for heavy worm burdens if they start with a significant count. There is no problem drenching ewes as close as 2 weeks out from lambing if handled carefully and it will not affect the developing lamb.

Hoggets/white-tag lambs: If there is no recent worm count information, check now and if no signs of worms, then WormTest again at 4–6-weekly intervals. Young sheep may be suffering an unrecognised growth rate penalty due to moderate worm burdens, which cause few visible signs.

Scouring in this age group in winter is usually due to worms, even if counts are low on average. This is usually due to an immune response, indicating that they have met enough worms to trigger their immunity. If a significant percentage— say, 20% or more—are scouring or have significant dags, a drench should be given. Provided they are in good body condition, they should maintain low to moderate worms burdens over the next few months, but monitoring is needed to ensure these don’t affect growth rates.