I once took pity on a Manx wether I had bought in for his fleece. I left him in with his sister and ran all bar the tups together. Well he was a total wee sh!t3, attacking the ewes and when they went into labour trying to make them stand by pawing at them and trying to mount them. So he went straightaway in with the big boys and suddenly HE was the object of intense interest by big males

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Ewe lambs I like to leave with their dams so they can see what lambs and lambing are all about - I'm sure it helps. The only time I had any problem was with a couple of Soay shearling gimmers who were so excited about something new that was smaller than them that they were pests from time to time, but nothing like that wether. Now anything male is taken out at 4 months, and only a full tup goes back at tupping time for just 4 weeks.
For whether or not to feed concentrates it really does depend on whereabouts you are, so please give us some indication. I live in Scotland on a very cold and draughty hilltop, but with good grass (even that though looses it's nutritional value once it's been frosted or snowed on, and we get a lot of that). I keep only Primitives now, and I give them some concentrates leading up to lambing, plus willow branches when available. They really don't need anything like as much concentrate as commercial sheep, just a handful each of 16% coarse mix, gradually increasing that a bit once they demolish what you've given them within seconds. Judge how much to give by how much they take - Primitives are not greedy. if they are not used to it, they may turn their noses up at it initially, but keep going.