Hi Mark
We lamb in April. There is not usually any new grass growth up here in our part of southern Scotland until then. Our ewes lamb outdoors and by April the weather is generally ok, although we do get the occasional emergency blizzard. We now keep primitive breeds which have to be kept over to 16 months if they are going for meat and that fits in neatly with an April lambing as they go off in the following August (we mostly supply the family, or sell any surplus direct to regular customers).
We used to keep Jacobs and there was heavy pressure to lamb them in January, to get them to a large size before the August shows and sales. We didn't even try it so our lambs were about half the size of everyone else's

We tend to prefer to do everything in as natural a way as we can, and lambing in April is the norm for most sheep breeds, after putting the tup in in Nov. The thought of going out to see to a ewe on a dark and freezing January night really doesn't appeal, whereas the wonderful starry nights in April are lovely.
Really it boils down to what suits you
