@fify-- That's why this breed is called "hair sheep." Or more accurately, Katahdin sheep is a type of hair sheep, there are other types.
I would like to mention that although the natural shedding is one of the most desirable characteristics of this sheep, it does depend on how pure the breed is. The more Katahdin sheep breed with other types of sheep, the more they lose their shedding characteristic. In order for Katahdin to continue shedding, they need to remain hair sheep genetically. So breeders need to keep this in mind. A true Katahdin's coat will shed completely in the summer.