Controlling Lice in Sheep

Background

Sheep lice cost the Australian sheep and wool industry more than $71 million in treatment costs and lost wool production each year.¹ Economic losses include reduced wool value from cotted fleeces, decreased fibre length, fleece weight, staple strength, style, and colour. 

Lice infestations cause intense irritation, with sheep frequently biting themselves or rubbing against trees and fences leading to fleece derangement, cotted or broken fibres. This intense itching usually occurs early in the infestation process until the animal becomes used to the parasite. 

Lousy wool often has a yellow colour and a distinctive smell caused by skin secretions. The sheep’s natural immune response to lice may cause thickening of the skin and pelt damage (e.g. cockle). Other causes of fleece derangement include itch mite (Psoregates ovis), dermatophilus, fleece rot and grass seeds. 

The body louse spends its entire lifecycle on the host animal, meaning that infestations are mostly spread via direct contact. Adult females lay their eggs on wool fibres within 12 mm of the skin. Eggs require a temperature of 35–39°C and a relative humidity of 50–70 per cent for optimal development. Eggs take 8–10 days to hatch before progressing through three nymphal stages over 21 days. Mature females lay about two eggs every three days and lay an average of 30 eggs during their lifetime. 

Off-shears control options 

Shearing significantly reduces the size of the lice population by physical removal and subsequent exposure to the elements. This makes immediately after shearing an ideal time for sheep and wool producers to apply a pour-on ‘backline’ treatment to control lice infestations.  

Short wool control options 

Dipping short wool sheep is a cost-effective alternative to pour-on treatments. Saturation dipping with either a plunge or cage dip is acknowledged as the most effective method of lice control. Complete saturation of the sheep with diluted chemical ensures contact between the target pest with the active ingredient.

Long wool control options 

Despite the best care and attention, lice infestations in long wool can occur and have a severe economic impact. A long wool lice treatment may be necessary to reduce lice numbers and minimise fleece derangement until the next shearing.  

Management considerations for managing lice

• Treat all sheep on the property at the same time. Avoid split shearing.  

• Muster each paddock thoroughly to ensure all sheep are treated. Conduct a second muster if necessary.  

• Do not mix treated sheep with lousy sheep or those of unknown lice status.  

• Check boundary fences to prevent untreated or lice-infested sheep from joining treated mobs.  

• Quarantine all purchased (e.g. rams, replacement ewes) or returning sheep (e.g. coming back from agistment) until you are sure they are lice-free. If lice are suspected, shear and treat with an effective off-shears backliner or short wool saturation dip. 

 • Sheep that require treatment with a long wool lousicide should be re-treated with an off-shears lousicide at the next shearing. 

 • Follow biosecurity guidelines when entering sheep properties to ensure no inadvertent spread of lice e.g. lice can be spread via shearer’s moccasins.  

Importance of Chemical Rotation

Parasite resistance may develop to any chemical if it is used continuously.  

The following guidelines will help to ensure sheep and wool producers continue to have access to a range of effective lice control options:  

• All lice treatments should be applied as part of an integrated pest management program (visit www.liceboss.com.au).  

• Avoid the consecutive use of lousicides with the same mode of action.²  

• If consecutive use of the same chemical group is required, careful attention should be paid to achieving eradication after treatment to help prevent the establishment of a resistant lice population.  

• Rotation between products with different modes of action may prolong the effective life of all available treatments.  

• Do not use the same mode of action for lice control and flystrike prevention during the same season.² 

Trusted solutions and advice from Elanco  

Elanco is an industry leader in sheep lice solutions with a product range including Extinosad^™ Pour-On, Viper^™ Pour-On, Piranha^™ and Extinosad Eliminator coupled with benchmark technical support and customer service. For any information or technical advice on managing sheep lice, contact Elanco 1800 995 709  or email productsupportau@elancoah.com