This chapter aims to summarise the wide variety of conditions that may be involved in states of emaciation, wasting, and loss of productivity in sheep. These wasting conditions signifi- cantly impact animal welfare, decrease production, and cause premature culling of animals in sheep flocks. They are complex diseases, and their presence can sometimes go unnoticed or underdiagnosed, seriously compromising the economic viability of production systems. Furthermore, the loss of body condition in sheep is sometimes masked by the presence of the fleece. Therefore, it is imperative to avoid underdiagnosis and seek early diagnosis to implement effective control measures.
