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Beyond the Bale : December 2014
32 ON FARM Grazing management improves worm control by: • avoiding paddocks heavily contaminated with worm larvae • reducing contamination of paddocks with worm eggs • allowing time for most of the eggs and larvae on the pasture to die. These paddocks are only required for lambing ewes or weaners to use in the few months when they are most susceptible. The latter two points are used when preparing low worm-risk paddocks. Grazing management to produce low worm- risk paddocks can dramatically improve worm control if four key guidelines are followed. Producers can try it with just one or two paddocks initially, to see the result. Effectively use the paddock during the preparation time without further contaminating the paddock with worm eggs Do this by any of the following (goats and alpacas must also be included): a. Keep sheep off the pasture, so no worm eggs can possibly be deposited. But you can use the paddock freely with adult cattle or cows and calves, for cropping, haymaking or new pasture establishment, or simply spelling to let pasture regrow. b. Graze sheep on the pasture only when they are not depositing worm eggs – that is, for a time immediately after they receive an effective drench (after a short- acting drench: three weeks in barber’s pole worm areas and 30 days in scour worm areas; longer if a mid-length or long-acting treatment has been used and where persistent protection has been confirmed). c. Graze sheep on the pasture when the worm eggs they deposit can’t possibly develop to infective larvae for continuous lengthy periods: • during very cold weather where maximum daily temperatures are under 16°C in winter rainfall areas and under 18°C in the summer rainfall areas, regardless of rainfall; or • when there are extended periods with no rain, regardless of temperature. Allow 3–6 months (depending on temperature) before use for at least 90% of the existing worm larvae to die These periods are generally effective for paddocks that will start their use at the time shown below: STARTING OF PADDOCK USE PERIOD BEFORE USE FOR LARVAL DIE-OFF Mid to late summer 3 months Early spring 6 months in cold frosty areas 5 months in temperate areas Mid autumn/ early winter 4 months While it might seem that even a seventy or eighty percent reduction in larvae survival is substantial, it is not enough for this strategy to be effective, irrespective of the initial level of contamination. Figure 1 opposite, shows a range of temperatures and the proportion of an initial population of barber’s pole worm infective larvae (scour worms are similar) surviving over time, depending on the daily maximum temperatures. SHEEP WORMS LOW RISK PADDOCKS Cattle can be grazed on paddocks during the time when the paddocks are being prepared • Effective grazing management reduces the exposure of sheep to worms. • There are four key guidelines to follow to ensure sheep suffer less from worms and need fewer drenches. • Timing of paddock preparation varies across regions but uses the same key principles. 1 2