Lice infestation is an endemic problem for Australian sheep, and infestations can negatively affect fleece weight, quality and yield. Decreased production and lower wool quality cost the industry more than $123 million each year*, which includes chemical treatment and prevention. Controlling lice successfully requires the integration of several strategies, including biosecurity, monitoring and treatment.
Australian sheep are most commonly affected by the sheep body louse or chewing louse (Bovicola ovis). It is a small wingless insect, with a red-brown head and pale brown striped abdomen, with adult specimens measuring approximately 2 mm in length. Lice are parasitic, and when they ingest dead skin cells and fat secretions, they irritate the sheep’s skin. This constant and intense irritation causes pulled and cotted wool.
The average louse’s life cycle is between 31 to 34 days. When eggs are laid, they attach to wool fibre and hatch after 10 days. These ‘nymphs’ mature in three stages over 21 days, after which they reach full maturity. Unlike adult lice, these nymphs tend to live on the sheep’s skin itself, rather than in the wool fibre. They also lack the abdominal stripes characteristic of adults. Three days after reaching maturity, adult females begin laying two eggs every three days until death
Lice best survive at constant temperatures of 37°C (a sheep’s average body temperature), moving to the upper part of the fleece if conditions are warm and shaded. Lice must have a host and cannot survive away from animals for long on fences or in sheep yards. They spread through direct contact between sheep, although some transmission through shorn wool is theoretically possible. The spread of lice usually occurs during yarding, camps and transport.
* “Assessing the economic cost of endemic disease on the profitability of Australian beef cattle and sheep”, Sackett, D et al MLA publication AHW.087 April 2006.