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Beyond the Bale : September 2019
48 ON FARM If there has been no evidence of lice at shearing for a few years, it is time to reconsider whether you need annual treatments. WHAT DRIVES THE NEED TO TREAT ‘JUST IN CASE’? A common misconception is that if lice are not treated at this shearing, there will be significant fleece damage from lice by next shearing. However, that may not be the case. If lice are present, but not detectable after carefully examining the most rubbed sheep in the mob, and shearers have not seen them, then lice will be in very low numbers on any sheep. The fewer sheep infested at that time, the longer they will take to spread across the mob and cause damage. You can use the LiceBoss Long Wool Tool to assess likely cost of fleece damage, based on the number of sheep rubbing. A second misconception is that a treatment applied at shearing will protect the sheep against re-infestation. While most sheep lice treatments provide a few weeks’ protection, they don’t have a long residual period effect. Therefore, sheep are not protected for most of the wool-growing year anyway, despite treatment. SPREAD OF LICE WITH INTRODUCED SHEEP Often, lice are introduced on just a small number of sheep, such as strays or rams, resulting in a much slower build-up of lice than if a large number of infested sheep are introduced, such as with a mob purchase. Similarly, the number of lice on each sheep being introduced will affect the rate of build- up across the flock. A heavy infestation will create a larger base population of lice, which will increase faster than from sheep that have a light, undetectable infestation. The time of introduction also matters; introductions earlier in the wool-growing year will have longer to build than ‘JUST IN CASE’ LICE TREATMENTS: TAKE THE PLUNGE, AND STOP recent introductions. Also consider the likelihood of introductions. While you directly control bought-in sheep, straying generally depends on sheep being on neighbouring properties and the quality of your boundary fencing. Before a ‘just in case’ treatment, consider whether introduction of lice has even been likely in the past year, as well as the timing and potential numbers of sheep bringing in lice and their possible level of infestation. ONGOING LOW-LEVEL LICE INFESTATIONS Where treatment occurs each year, but doesn’t actually eradicate the lice, there are two likely causes: 1. The entire flock was not treated correctly, despite using effective chemicals When some sheep miss treatment or are poorly treated, lice can remain to re- contaminate the flock. With lice present since this treatment, it is more likely that lice will be detectable at the next shearing. This still may not be causing extensive fleece damage, but should be treated, with attention to complete musters and thorough application. 2. The product used was not completely effective Resistance to Synthetic Pyrethroids (SP) is widespread and resistance to the Insect Growth Regulators (IGR) is common. If an SP or IGR has been your recent treatment product, many of the sheep may have a surviving lice population, which is quite likely to be detectable by the next shearing. Consider changing to a known-effective product for your next treatment, combined with complete and effective application, then reconsider annual treatments in the following year. It’s also possible that you may have been using these products annually, just in case, with no lice present anyway – you may have eradicated lice years ago. TAKING THE PLUNGE Consider taking the plunge away from lice treatment at your next shearing; be ready to treat if lice are found, but prepared not to. 1. Check before shearing A few weeks before shearing, catch the 10 scruffiest, most rubbed-looking sheep and Modern lice treatment chemicals are highly effective if applied properly. Viper® backline application, image courtesy of Bayer Animal Health. Many properties have eradicated lice forever and never apply a ‘just in case’ treatment annually, but some producers are yet to take the plunge.
In the Shops - September 2019