Hi - we shear our lot twice annually for a variety of reasons. First up is that they are Longwool sheep, and therefore grow big, heavy fleeces, so during the spring months if they were in full fleece and we had a hot spell, they would basically overheat, not to mention they are more prone to fly-strike than most, regardless of how much pour-on we apply. Also, we house them in winter, and generally shear towards the end of January / beginning of February in order that when they lamb, we can see what's going on at the rear end, and also so the lambs don't end up strangling themselves in the long fleece. Due to the remarkably low price that one gets for wool these days, this is not particularly cost effective, but does ensure that the sheep have a better quality of life, and makes lambing a whole lot easier..
Hope this helps.
Catherine.