Fleece derangement of merino sheep infested by the itch mite Psorergates ovis

Abstract

Extract

Fleece derangement, characterized by matted chewed wool in a region accessible to the sheep's mouth — i.e., behind a line approximately from elbow to hip, — indicates a typical behavioural response by sensitive sheep infested with Psorergates ovis. The condition was recorded by Bekker (1928) long before the mite was found (Carter, 1941; Womersley 1941). Fleece derangement is seen easily at flock inspection and so is used as anindication of P. ovis infestation in a flock, though Baker (1968) showed that a greater proportion of sheep in which heavy skin scurf was present, with or without fleece derangement, may be infested. Inspecting individual sheep closely for scurf is slow, while examining skin scrapings limits the number of sheep that can be inspected to less than about twenty per day, so the ready convenience of observing fleece derangement favours its use.