if they are heavy bred and huge there may not be much room in there for them to eat much, its better they are eating the hay and graze then grain...as long as they are behaving normal other wise... I would just keep a good eye on them
they should be chewing a cud..peeing pooping berries, bright eye,alert and have deep pink to red inner eye lids...eating and drinking well...
I bet they want grain once those babies are born..
B complex if 4 cc per 100#sub Q