Gorgeous mare! Any pictures of the stud?
I'm not terribly experienced, so some of the more seasoned breeders on here can probably tell you a little more, but I can share some information, based on my own experience.
I based my mare's feeding on her weight, because she gains weight very easily. She is at 313 days now and has been on a very strict diet because she is such an easy keeper. She would get about 20 lbs of timothy/alfalfa hay per day and then starting at month 8, 4 lbs of mare & foal feed. Basically, if you're feeding hay and supplementing with a broodmare ration, she's probably going to be in good shape. If she is losing condition, then you can increase her feed and vice versa if she's gaining too much weight. I've relaxed a little now on my mare's feeding regimen because I've noticed she's a little ribby and I'd like her to have a bit of a buffer, especially since now she is starting to develop an udder.
I wish I could answer your question about fescue. We don't really have bermuda hay up here (at least we don't call it that), so I don't really know that answer. Hopefully someone else can answer that question.