Each mare is very very different and I have mostly TB mares here too
The Pearlescent mare is a tank. A complete and utter 16.2hh, WB built tank, and she will eat anything and everything put in front of her and maintain her weight I always have to remember that she is feeding a growing fetus as well, so as well as free choice 2nd and 3rd cut alfalfa mix hay, she gets 4 lbs a day of 16% Buckeye Growth formula for mares in foal, weanlings / yearlings and 2 lbs a day of the ration balancer Buckeye Alfa Grow N Win
When she is not in foal or lactating she gets cut down to about 3 lbs a day in total
My Puchi Trap mare has always been a hard keeper. Where I had her before they fed ShurGain and at 12-14 lbs a day of 14-16% broodmare feed, plus free choice hay, she looked utterly awful and gaunt even leading up to foaling. Plus she was a picky eater and there was SO much grain in her bucket, she was totally backing off it, sighing, looking at it like it was poison and standing in the corner glaring at her bucket.
I now have her on Buckeye as well now that we have our own place, and not pregnant, she is getting 2 lbs a day of Grow N Win and 4 lbs a day of Buckeye Trifecta which is a 14% fat product that really packs the weight on them. When she is in foal, she gets Growth added in there as well and probably a total of 8-10 lbs a day of grain and I find with her, I absolutely HAVE to give her that much or you can see ribs and hip bones sticking out. She still - to this day - is a very picky and slow eater and will take all night long to finish her dinner - she just picks at it very very slowly ...
Hope that helps a bit - you really wont get the broodmares "hot" at all - the babies are taking so much nutrition from them, the feed is going more to baby than it is to them at this point ...
Good luck with her!