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Western Australia worms, flies and lice update - April 2015

WA WormBoss Worm Control Programs

WA WormBoss Drench Decision Guides

Albany: Brown Besier, DAFWA (

The recent good rains across most of the state have started pasture growth, and with it, the worm cycle. Worm eggs will be developing in far greater numbers than a month ago, and it’s important that sheep now carry close to zero worm burdens.

The advice given last month still applies: an urgent drench is needed for any mobs where it is not certain worm counts are very low.  The vast bulk of mobs will have been given a summer drench (especially lambs and hoggets), or if ewes, a drench in autumn.

However, where sheep are still putting significant numbers of worm eggs out onto the pasture, there is a danger that this will set up problems in winter and spring.  The main reason for continued high worm burdens is that drench resistance reduced the effectiveness of the most recent product used. At a minimum, drenches at critical times (summer and autumn) should be 95%, and ideally close to 100%, effective.

If in doubt, a worm egg count on suspect mobs will quickly indicate whether good control has been achieved, or a follow-up treatment is needed.

Pre-lambing drenches to ewes: for ewe mobs drenched in autumn and due to lamb in late April or May, worm burdens are almost always too low to justify a pre-lambing drench. However, if ewes were drenched in summer, or have not been drenched at all since last year, a worm egg count is strongly recommended to check whether this drench is needed. Even a low count will be magnified over the lactational period, as ewes spontaneously lose their immunity for about 2 months after lambing.

If average egg counts 2–3 weeks out from lambing are over 100 eggs per gram, the mob should be drenched. If in a barber’s pole worm area and the count is over 200 eggs per gram, it is a good idea to request a test for the worm species, as if mostly barber’s pole, a long-acting drench may be recommended.

So far, the early rains bode well for broad-acre agriculture in WA, but along with weeds and insects, there is a greater risk of worm problems. More worm egg count monitoring will be needed this year compared to years with more traditional weather patterns.

Perth region and Central Wheatbelt: Ray Batey, Sheepvet Australia (

Managing larval contamination—the key autumn objective

Recent worm egg counts for some clients have revealed increased worm egg output across all age groups since monitoring last October, with a large variation between individuals. Sheep are in good condition and nutrition does not appear to be a factor.  Multiple worm species appear to be involved, with Haemonchus implicated on at least one property.  It is likely that late spring rains, summer showers, and early autumn rains have facilitated greater larval survival and pickup than ‘normal’ on some farms.

It is important to recognize that pastures on which sheep with high WEC are or have been running are likely to present high larval contamination and survival rates at this time. This presents an increased risk of contaminated lambing paddocks, with grazing management likely to be as important for risk mitigation as the choice of treatment.

It is important to make decisions appropriate to each circumstance. One client with elevated counts in half his adult ewe mobs has opted to monitor affected sheep and delay treatment until they are moved onto prepared lambing paddocks. In the meantime, those mobs are being used to crash graze and clean up other paddocks prior to cropping. Other clients less able to manipulate the grazing-cropping cycle have treated early with further monitoring of younger ewes scheduled for mid-winter.

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