Being mean with the hay

We are fast running out of hay, as is everyone, so in order to preserve our diminishing stock we are being quite mean with who has and doesn't have hay.
Our original plan was to give all the sheep Barley straw through November and December, whilst there was still grass for the sheep to eat. We'd bought in 130 bales of straw just for that reason. But with the sudden arrival of the snow, the sheep went straight onto the hay. But over the last few weeks we've been cutting down the hay the gimmers have, and giving them the straw instead. They had a bit on a whinge about it. But now they are quite used to the straw. We've also started to give the ewes straw, every other day, and on fine mild days, shut them out of the barn so that they go out and eat the grass.
It seems to be working, we are not going through the hay as fast as we were and we've been able to source another 100 bales of hay, which should at least last us through to lambing!
In many ways it is cheaper for us to feed the sheep a concentrate feed, but as the ewes are in lamb we have to be careful how much concentrate we given them, as over the last 2 - 3 weeks of pregnancy, all excess feed goes into the lambs, so we have a delicate balancing act of giving the ewes enough feed so they don't loose condition, but not too much that the ewes have BIG lambs.