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Beyond the Bale : December 2018
50 ON FARM What actually happens to worms during long dry periods or drought? And how are they best controlled during these times in those (normally) moderate to high rainfall regions where worms are normally present? DROUGHT: WHAT HAPPENS TO WORMS? Many livestock producers are surprised to find sheep severely affected by worms during a drought, or are dismayed when sheep succumb to worms soon after it rains. In regions where drenching is normally required, worms will still be present in drought, and lighter sheep will be far more susceptible. Regular worm egg counts indicate when drenches are required, preventing losses, especially of poorer sheep. In the normally lower rainfall areas, regardless of drought, it is usually sufficient to monitor worm egg counts about 6 weeks after there has been enough rain to generate a green pick (new green pasture). Recommendations for the moderate to higher rainfall areas are detailed below. WORMS IN THE SHEEP The first source of worms is the sheep themselves; they carry worms into a drought, and can suffer the ill effects many months after conditions have turned dry. WORMS ON THE PASTURE The second source is worm larvae, which live for many months on the pasture, despite dry conditions. IN THE FIRST 6 MONTHS AFTER THE RAIN STOPPED Larvae not ingested with pasture die, not because it is dry, but because they run out of stored energy, as larvae do not eat. The majority – about 90% – die in about six months under cooler conditions, three months under hotter conditions, and even faster when extremely hot. Very few survive more than one year. Therefore, larvae that hatched in wetter conditions before the rain stopped may be on the paddock for many months despite lack of rain. When the sheep eat the contaminated pasture, especially as they graze lower and lower, the larvae are ingested and some establish in the sheep. Worm burdens in the sheep can rise quite quickly when they lose condition, because under-nutrition reduces their immunity to worms. PARABOSS: BEST PRACTICE ADVICE FOR MANAGING SHEEP PARASITES ParaBoss is a suite of three products – LiceBoss, WormBoss and FlyBoss – developed to help sheep producers in the management of lice, worms and blowflies. The LiceBoss, WormBoss and FlyBoss websites are sources of detailed management information and regional programs that will assist in managing the major parasite risks for sheep. The websites have been developed by expert panels of parasitologists and veterinarians from across Australia. ParaBoss provides access to the three websites at www.paraboss.com.au. Subscribe to ParaBoss News, the twice monthly free email newsletter with state outlooks on the current state of sheep parasites as well as feature articles and the quick quiz to test your knowledge of sheep parasites. You can subscribe on the ParaBoss website. Join us on Facebook at www.facebook.com/paraboss.com.au to see weekly posts on flystrike, lice and worm control. ParaBoss is funded by AWI and MLA and coordinated by the University of New England with industry oversight. MORE INFORMATION www.paraboss.com.au But by about six months from the last significant rain (10–15 mm or more over a few days) that source of larvae has declined to very low levels. WormTest each 1–2 months, in both normal years and the first 6 months of drought: • Barber’s pole worm areas: 4-weekly in warm months; 6-weekly in cooler months • Non-barber’s pole worm areas: 5–6 weekly for young sheep; up to 2-monthly for adult sheep in good body condition on better feed. AFTER THE FIRST 6 MONTHS SINCE THE RAIN STOPPED Once most of the worm larvae that developed prior to dry times have died, new worms can only originate from new contamination, that is, from the worms living in the stock during drought. The question is: will the worm eggs being passed in dung that is landing on a dry paddock survive, develop to infective larvae, and become available for ingestion by the stock? Generally, all nematode worm species will hatch and develop into larvae within a moist faecal pellet and then move out onto the pasture. However, the brown stomach worm (Teladorsagia) and black scour worm (Trichostrongylus) are able to survive within the faecal pellet for weeks during very dry times, except with extreme summer heat. Barber’s pole worm (Haemonchus contortus) has less ability to do this and will generally die within a week or so if there has not been about 10–15 mm of rain. If sufficient rain dissolves the dung pellet, any living scour worm larvae are released onto the surrounding ground and they can move onto the new pasture and be ingested by stock. But while it remains dry the risk is low. There is some concern that sheep eat dirt with pulverised dry dung when eating grain trailed on the ground and will gain a worm infection under these conditions. However, there is no evidence of significant pick up of these larvae from the ground when the paddocks are dry with little or no pasture. It’s not until some green pasture has developed that the new larvae that were
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