I have my expectant does on a good quality alfalfa hay. I supplement with grain or goat feed with BOSS (black oiled sun flower seeds) mixed into it. They get the grain twice a day - I start out with about two cups and work up through their pregnancy until they are getting 7 to 8 cups twice a day at freshening. I do have large dairy breeds... so a smaller breed would be different in the amounts.
Just try to make sure the doe's body condition is good. Too fat or too thin, and you're risking ketosis/toxemia of pregnancy...not something to fool around with. The kids do most of their growing in the last 2 months of the pregnancy, to watch her closest then.. Again, just keep her condition up.. If you really shovel the grain to her in that last little bit, you may wind up with bohemoth kids that she can't pass..so that's something else to consider.
Make sure she's got access to good loose mineral, too, and keep it in shape enough that she'll actually use it. They're bad to soil their mineral just like they soil their hay or grain, and sometimes they just stop eating it without the herdsman really realizing it.