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South Australia worms, flies and lice update - July 2016

SA WormBoss Worm Control Programs

SA WormBoss Drench Decision Guides

Adelaide: Colin Trengove, Sheep Health Lecturer (UA Roseworthy campus) (

Winter has arrived with gusto…. much wind, copious rain and single digit overnight temperatures. The implications for parasites are good. Worm development conditions on pasture are ideal, with the exception for Haemonchus contortus (barber’s pole worm) that won’t develop to infective larvae during frosty conditions. Similarly, flies can’t cope with these conditions, but lice delight in the microclimate away from sunlight and close to the warm skin.

Worm egg counting tends to be minimal mid-winter as feed on offer is mostly adequate and ewes are either late pregnant, lambing or lactating. Most monitoring during May–August in southern Australia occurs either preceding lambing, as a check on the need for a pre-lambing drench, or in the lead up to weaning. Lambs rarely need a drench at marking, as their exposure to worms on pasture has been minimal, with the possible exception of drought years. However, many producers adopt the conservative approach of routinely drenching ewes pre-lambing, without checking worm burdens, as an added insurance against worm concerns prior to marking.

There have been several recent reports of ewes going down in the lead up to lambing as well as in the first few weeks post-lambing. A thorough investigation by your veterinarian should confirm the cause, but my suspicion is hypocalcaemia (milk fever) in many instances. What has this to do with worms? Any stress on ewes in the last 6 weeks of pregnancy, especially those bearing twins, increases the risk of hypocalcaemia. Management procedures such as yarding, drenching, vaccinating and moving should be kept to a minimum during this period and in particular the last 2–3 weeks before lambing. Conditions that predispose to hypocalcaemia in the weeks prior to lambing, apart from droving and yarding, include prolonged grain feeding or grazing lush green feed without providing a calcium supplement. The diet during this period only requires 1% calcium (e.g. stock lime or various loose mineral mixes) added to prevent hypocalcaemia. If you have experienced ewes appearing weak or becoming recumbent and subsequently dying under the conditions described, a lack of calcium could be the explanation. Lack of magnesium and phosphorus can also cause similar problems and so a diagnosis by your animal health advisor is advantageous to determine the best treatment and prevention.

As weaning approaches, a worm egg count is useful to assess the effectiveness of the winter worm control program. It is also time to decide upon the most effective drench to use if monitoring indicates suboptimal winter worm control. Weaning paddocks should have been chosen several months ago and prepared to ensure that weaners can grow at an optimal rate without the handicap of a developing worm burden. Feed quality should not be a concern at this time of year, but the amount should be at least 4 cm high and dense, i.e. covering the heel of your boot or at least 1200 kg Dry Matter (DM)/hectare (ha).

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