Steve's advice sounds fine for good southern ground.
If you're on a Cumbrian hill farm, you'll either send your ewe lambs away to kinder ground for their first winter or will be feeding them from October onwards if you want them to grow right, so you would definitely need to be putting some cake into pregnant ewe lambs. You will also need to cake any Blue-faced Leicester tups from 6 weeks before tupping right through tupping and probably for the remainder of the winter afterwards.
So calibrate this sort of advice against your local conditions. But as Steve says, manage to condition score and you won't go too far wrong.