Sheep Lice

Sheep lice affect the health of an entire flock. The most common sheep body louse, Boicola ovis, infects sheep throughout the world. Economic impacts include decreased wool prices and animal productivity. These biting lice spread within a flock very easily, and effective lice control depends on animal management and chemical treatment. If not controlled, lice numbers increase very quickly.

  1. Identification

    • Lice live their entire lives in the wool of the sheep. Wingless and very tiny, about .08 of an inch long, the creatures inhabit the outer layers of skin, where the wool emerges. Parting the fleece allows viewing of lice at the base of the wool hairs. They like to congregate in the neck area of short wool sheep and side area of long wool sheep.

    Life Cycle

    • Lice complete their entire life cycle on sheep. They congregate in areas where the wool grows, not the face or udder. The female louse lives only 30 days. She lays 10 to 20 eggs, which hatch in nine to 10 days. It takes about 35 days for the hatched lice to mature.

    Effects

    • The feeding action of the lice on the skin irritates the sheep. Sheep may rub themselves against objects to get relief. The rubbing damages the wool by matting the fibers together and sometimes tearing them. Such self-inflicted trauma causes fleece loss and damage. High lice numbers predominate in late winter, when the wool is long and the sheep live in close quarters.

    Treatment

    • Controlling lice depends on appropriate animal management and chemical treatment. Shearing sheep removes 90 percent of lice. Lice exposed to the environment will die quickly. Shearing benefits chemical treatment of lice, but not required. Chemical treatment involves walking sheep through a chemical water bath containing organophosphates. Chemical treatments reach the skin easier with shorter wool. Topical backline (along the back) applications, such as cypermethrin or deltamethrin, control lice, too.

    Significance

    • The economic effect of lice on wool and productivity depend on wool condition, amount of wool, type of wool affected and sheep marketability. Matting and discoloration decreases values of highly profitable wool types. More lice means more damage and less profit. Many buyers refuse to buy lice-infested sheep or wool.

    Prevention/Solution

    • Sheep need close inspection for lice before introduction to a flock. Lice spread rapidly by direct contact. So if lice are found, isolate the infested sheep from the rest of the flock and treat accordingly. Lice not only transfer between animals, but between flocks on shearing clothes and equipment. Moving between flocks requires decontamination of all reusable items.