What is in dairy grain? Anything you do, do it gradually so they do not bloat from a diet change.
In the Summer my goats eat a lot less of their normal feed, since they have acres to graze from, but they still need feed if they are milking, nursing babies and of course growing babies. As soon as the land goes brown and it gets cold I start upping their feed and buying giant bales of hay.
Everyone feeds differently and you have to find what works for you. I feed...
2 parts alfalfa pellets
1 part grain 3 or 4 way
a small bit of BOSS ( black oil sunflower seeds)
They have a 700 pound bale of grass hay and minerals available all the time.
This works for me with my dairy girls and they get enough calcium from the pellets that I have not had issues with it. But may not work for you cost wise, what you can find in your area and etc.
I also cut grain during the last month of pregnancy so they do not have huge fat babies. So they get just the pellets, hay and any forage that may have grown back.
Are you in a cold climate? If so you should start them back on the grain now, gradually of course