I normally don't really grain my dairy goats when they are pregnant, because they don't have as many babies as my boers do (thus not needing the grain), but when I do grain them, I grain them the first 3 months of pregnancy, and the last week of the 5th month, and all the way through lactation. I grain them 2lbs a day of 18% protein (grain mix or pellet). If I do end up graining the dairy does all through the pregnancy, I start out with 2lbs a day for 3 months, then I drop it to 1lb a day the rest of the pregnancy. When they kid I give them 2-3lbs of grain per gallon they milk.
For my boers they get 2lb all through pregnancy and lactation.