A common winter issue, lice are prevalent at this time of year due to their preference for cooler, darker and drier weather conditions. Infestations develop as a slow burn on healthy animals, with numbers gradually increasing on individuals. The entire lifecycle of lice is spent on sheep, so transmission between individual animals can only occur following very close contact. For example, a lice infested ewe will infect her lambs within 24 hours as they feed and remain close to their mother.
Lice infestations have a serious impact as they stimulate an immune response in the skin of a sheep. This can lead to damaged wool with reduced yield and quality as well as causing damage to the skin itself. The strong itch reflex triggered by lice infestation causes scratching which leads to further damage to the wool and pelt, also distracting sheep from grazing.
Sheep in good body condition are less susceptible to lice, so when trying to determine whether your flock has an issue, the poorest condition animals are the ones to check by parting the fleece and counting lice numbers at key locations across the body.
Fortunately shearing will remove the bulk of lice from an animal. In particular shearing during warmer weather will expose the lice and their eggs to increased UV light leading to a higher kill. However, for various reasons this might not always an option and chemical treatments are often required to help break the lifecycle.
Chemical treatment is best done when lice numbers are at their lowest – either in summer and/or immediately off shears. Winter shearing may provide the opportunity to do this. A range of products are available with a variety of application methods. The key is to use the product that will most effective for the situation at hand and to apply it properly according to the manufacturer’s recommendations. Products should be rotated every year to avoid resistance issues developing.
Any new sheep brought onto a property should get a quarantine dip. Treated animals should not be mixed with untreated ones. Regular monitoring will help ensure treatments are working properly.