what is sheep scab
1 Sheep-scab is a condition in sheep caused by infestation with a particular type of mite (Psoroptes ovis, known as the sheep-scab mite).2  This mite is a very small wingless parasite that you can only just see with the naked eye, and then only properly under a magnifying glass or a microscope. You may see wool in the mouth of the sheep and wool may also be found on fences and other objects against which the sheep rub. 2  Fluid leaks from the irritated skin, and dries to form yellow crusts or scabs. 3  This is why the condition is called scab. 4  You will see bare, scabby patches and matted wool.