Mae Clafr Defaid yn un o'r risgiau mwyaf o ran clefydau defaid a gellir ei ledaenu trwy fethiannau bioddiogelwch, patrymau symud cymhleth, a chymysgu defaid ar ffermydd ac oddi arnynt, megis trwy bori ar dir comin.
Sheep Scab is one of the major disease risks for the sheep industry and can be spread through failures of biosecurity, complex movement patterns, and the mixing of sheep on and off farms, such as through common grazing.