1. 43% of flocks in the pastoral zone and 29% of flocks in the wheat/sheep and high rainfall zones are infected with lice. This number was increasing due to resistance of lice to older chemicals and the ban on diazinon in 2009, however currently it is believed that the prevalence is stable due to effective chemicals being able to control and eradicate lice.
2. Sheep lice infestation can reduce clean wool cut by up to 1kg per head. This results from lice reducing yield, causing the fleeces to become cotted and yellow and increasing the losses during processing. This results in fleece values being reduced in the range of $3-$10/hd
3. There is little economic impact in the first year of an infestation. In studies where infected sheep have been introduced into flocks, there has been little effect in the first year, but reductions of up to 30 to 40% in the subsequent year’s fleece value occur as lice numbers build up in the flock.
4. The estimated annual cost of lice to the Australian sheep flock is $81 million This includes the treatment, prevention and production cost.
5. Lice have no effect on body weight, lambing percentage or growth rate. However, sheep with low weight gains because of poor nutrition or other stress may be more susceptible to lice and develop heavier infestations.
6. Spread of lice between sheep occurs almost exclusively by sheep to sheep contact. Therefore, if lice ban be eradicated from a flock and other lousy sheep excluded, the flock will remain lice free.
7. The best way to monitor for lice is to look for rubbing sheep. However, you must actually see lice to be sure they are not scratching for other reasons.
We will discuss lice in more detail in upcoming newsletters. Remember the best source of information is liceboss.
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