Parasites & Pests

The major louse affecting Australian sheep is the sheep body louse, Bovicola (formerly Damalinia) ovis. The parasite feeds on the fatty secretions on the surface of the skin. Sheep lice cause intense irritation to infested sheep, resulting in pulled and cotted wool, especially around the flanks.

The adult body louse is about 2 mm in length, and feeds on the surface of the skin.
The sheep body louse is relatively flat, with a red-brown head and pale brown striped abdomen.  Immature lice are smaller than adults, lighter in colour and generally found on the skin rather than in the fleece.

Lice are obligatory parasites, meaning that they only live on a host, and can only survive for a relatively short time away from it. Lice are said to be “species specific”, meaning that sheep lice only live on sheep. Goats, cattle ,pigs and horses have their own species of lice. Although sheep lice may survive on goats for a short period of time, they are not likely to be carriers of sheep lice.

Finding Lice

There can be anumber of causes of fleece derangement, including infestation with sheep body lice.  As lice are relatively small, good lighting and for those that wear them, reading glasses are also required, so that lice can be identified.  Select sheep that have signs of fleece derangement and part the fleece over areas where lice prefer to live such as the flanks and shoulder to search for lice.    If it is a light infestation, several fleece partings should be made along each side of the sheep in defined areas such as the neck, shoulder, ribs, flanks and rump.

Sheep should be routinely inspected for signs of lice prior to shearing, at crutching and any time that sheep are mustered including drenching.  This is especially important if
lice have been previously detected in the flock.

Life cycle

Economic Cost

In a report commissioned by the MLA* in 2006, the annual cost of lice to the Australian Wool industry was estimated to be $123 million.  For farmers, there are two main costs of having lice infested sheep.  Lousy sheep cut about 10% less wool and the value of the cotted wool is also reduced by about 10%. ( NSW DPI Agfact – A3.9.31,2001). 

A sheep lice infestation is likely to reduce fleece weight and staple strength, and adversely affect style, colour and yield. It has been estimated that fleece weight is reduced by 0.2Kg – 0.9Kg of greasy wool and clean wool is reduced by 0.3Kg – 0.8Kg per sheep due to fibre shedding. Lice also irritate the skin while feeding which increases suint and skin secretions, which in turn, discolour and reduce the value of the fleece.

Lousy sheep are also more susceptible to blowfly strike. As sheep bite at their flanks the wool becomes moist and attracts blowflies.

* “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.

Transmission

Sheep lice are obligatory parasites, meaning that they only live on a host, and can only survive for a relatively short time away from it.  Lice are said to be “species specific” meaning that sheep lice only live on sheep. Goats, cattle, pigs and horses have their own species of lice, and although lice may survive on goats for a short period of time, they are not likely to be “carriers” of sheep lice.

Away from their host, lice and their eggs can only live for a limited period of time.  Under laboratory conditions they can survive for several weeks, and for example, could survive for several days in shorn wool in a shearing shed, but will quickly die in sheep yards or on fence posts.  Direct contact with lousy sheep is the usual way that lice are spread, although transmission between farms on shearer’s moccasins is theoretically possible. Birds are often seen around grazing sheep, but are not known to transfer lice.

Lambs readily become infested if their mothers are infested with lice, and if not treated can potentially re-infect their mothers.