I might just stick with their usual feed, and do just oats for a week or so.
And then after I reintroduce their food, it's continuing free feeding oats, and add the measured amount of their food in a separate dish, right? Until the 42nd day when I wean her back onto a normal feed routine? If I leave it that long.
That all sounds right to me. Good luck! Really hope this works out well for you and your girls.