Lice are common parasites of sheep and less commonly of goats. Lice are usually host-specific meaning that different species of lice are found on sheep, goats, and cattle. Lice cause skin irritation and severely affected animals may exacerbate this by scratching and rubbing, further damaging skin and fleece. Transmission in a flock occurs when animals rub against each other.
Lice are very sensitive to heat, sunlight and humidity. Shearing and exposure to direct sunlight on short fleeces tend to discourage lice burdens, and lice are unlikely to be a problem in the export process unless the animal is otherwise debilitated. On goats, however, the louse population can increase explosively in stressed animals.
Clinical Signs and Diagnosis
Lice are small active insects that can be difficult to see in hair or fleece. Adult lice on sheep and goats are less than 2 mm in length with a red-brown head and cream coloured body. Lice may be seen under conditions of good lighting by quickly parting the hair or wool in or adjacent to irritated areas. They may be found anywhere on the body in heavy infestations, but may be localised to the head, neck, underbelly or ankles, depending on species, coat length and intensity of sunlight.
Grass seeds penetrating the skin is the main differential diagnosis when a number of animals in a mob are scratching and biting at themselves.
There are a range of pour-on backline preparations available to control lice. Shearing and exposure to sunlight will dramatically reduce lice populations.
Infested animals pose a risk of spread at assembly points. This is less common if animals are shorn, exposed to sunlight, and have been treated for lice on farm. Unnecessary chemical treatments during pre-export preparation should be avoided to prevent residues.