Several species of sucking and chewing lice infest sheep and goats. They are not normally as prevalent as sheep keds, though, and are seldom a problem in flocks that are treated for keds. The African sheep louse, sheep foot louse, and sheep body louse all suck blood from the animals, while the sheep biting louse feeds on skin scales and wool fibers.
Symptoms of lice include severe itching by the animal and rubbing on fences and other surfaces to relieve the irritation from the bites. Animals may rub and scratch until they denude areas of skin, and the wool of infested flocks becomes ragged and inferior in quality. Heavy louse populations cause anemia and make animals more susceptible to respiratory and other diseases. Lice are generally more of a problem in winter.
Distribution and abundance of these species are not well known. Eggs are attached to the hairs but can hatch even after being dislodged from the animals for several weeks. Immature and adult lice can survive for a week off the host. The eggs of the sucking lice hatch in 10 to 18 days; those of the biting louse, in 5 to 10 days. Females can begin laying eggs about 2 weeks after hatching.
Sprays, dips, pour-ons, and dusts are all effective for control of sheep keds. As a general rule, sheep should be treated in the spring after they have been shorn, when the weather is warm and the keds are most exposed. If animals are heavily infested in fall or winter months, however, it is advisable to treat them rather than allow the keds to continue to increase and cause losses. If you spray during fall or winter, select a warm, sunny day. Treat the animals in the morning, and keep them outside until they dry. To reduce the chances of illness, do not let wet animals crowd into a warm building. If all new bucks and ewes are treated before they are turned in with the rest of the sheep, treatment of the flock once a year will control sheep keds.
Application equipment that provides a nozzle pressure of at least 50 psi is adequate for ked and louse control on sheep. To ensure adequate and thorough dosage, do not spray more than 5 or 10 animals at a time. Confine sheep in a relatively small area so they will rub against each other and maximize the effectiveness of the materials being sprayed. Hold the spray nozzle a few inches from the wool, and spray the animals until they are thoroughly wet.