Yes it's a pain isnt it?
a combination of feeling fat, fed up, permanently peckish and yet too full of lambies to eat very much makes my girls pretty grumpy at the end of their pregnancy and they have a tendency to do the same if reunited in the late stages. Some more so than others.
As some of the head buts are belly blows and the situation results in lots of stressed and out of breath ewes, I avoid it until post lambing. My lambing shed is partitioned so I can keep them separate until after lambing which also accommodates those that eat too much and get indigestion pains, the ones that need coaxing to eat, the ones that get headbutted if they become distressed in labor and the ones that steal others lambs.
Ah the joys of sheep....thank heavens for hurdles and hinges!