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South Australia worms, flies and lice update - September 2017

SA WormBoss Worm Control Programs

SA WormBoss Drench Decision Guides





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

Following a dry July, wet August and now moderate September, most producers are satisfied with the season to date—albeit a little late for parts of the Eyre Peninsula and the York Peninsula. South east producers are experiencing above average moisture leading to inundation not seen for many years. This is generally great for production, but can also be accompanied by increased disease incidence including mineral deficiencies and parasite burdens. The impending warmth of spring signals the emergence of blowflies eager to find moist fleece in which to deposit their eggs, so vigilance is paramount for sheep health and welfare. Winter will also have bolstered lice populations and so parting the fleece several times on 20 sheep while in the yards is always prudent.

Worm egg counts (WEC) have followed the seasonal pattern with recent counts in lambs in the thousands (worm eggs per gram (epg) of faeces). Even WECs in adults, both dry and lactating, have been in the hundreds, while others are zero. This variation highlights the impact of season, grazing management and drenching strategy along with body condition, age and immune status. It also illustrates that worm burdens are unique to the mob sampled and cannot be extrapolated to another mob with any certainty. We are fortunate that worm egg counting is a relatively simple, cheap and reliable option to monitor worm burdens in small ruminants, as attempting to predict parasite numbers based on experience or history is, at best, guess work.

As a general rule in agriculture, we are unlikely to detect production loss until it exceeds 20% or more and so relying on observation and intuition alone is not going to achieve optimal production and profit. Internal parasites are no exception and as long as you have moisture in paddocks and/or adult worms in grazing animals they are a constant threat. The adage goes… ‘if you can measure it, you can manage it’…and WECs are a great example of this.

Significant populations of worms in lambs at this time of year provide an ideal opportunity to check the efficacy of the various drenches at your disposal. If the lamb mob WEC is at least 250 eggs per gram of faeces, then treating multiple groups of 15 lambs with different drenches and then rechecking the WEC in each group in 2 weeks will indicate how effective each drench is at eliminating the worm burden. This information then allows you to plan your use of drenches over the next 2–3 years. Seek advice from your animal health advisor if you need any assistance in setting up drench trial.

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