We have had calcium / prolapse issues doing this , vet says we need a slow release calcium bolus like dairy cows have pre calving but no one makes them for sheep , apparently the roots are to high in calcium and the ewes can't utilise it , also the turnips start to b olt in march loosing their goodness just when iit's most needed . I don't like using turnips for in lamb ewes but that's what we have , I hope to try making some high quality hay available to them this time , fodder beet didn't help last year as they are high in calcium to but great on the grass post lambing .Sorry, I'm wrong. It is other way around. I know neighbours who have grazed stubble turnips up to lambing, then lambed on grashttps://www.bbc.co.uk/news/world-asia-48019189s. They have had issues with twin lamb that I put down to the food change at a critical time