Now that it's been a couple of months, I've really been noticing her losing muscle and it seems like she's gotten "skinny".
However, I'm really not sure if that "skinny"-ness is due to her losing muscle in places that made her look more filled out, or if she's legitimately lacking nutritionally.
The main area I'm noticing is her ribs. When she has her coat flattened down (right after her blanket comes off), you can see them all when she breathes in. It's easy to feel them but you do have to gently press to get a good feel...
I've noticed other areas that seem to be "lacking" but I'm sure those are due to muscle loss: she doesn't seem as wide as she once did, her shoulders are less huge, her booty is less QH-y, etc.
Anyway, how does one work muscle-loss into their horse's body condition scheme?
She should be getting enough for what is (not) being asked of her and her activity levels are great (she spends at least 10 minutes each day running around like a maniac, bucking)... At least, she always came through the winter chubby when she was in work and eating less than this...
[also, she IS nearly 28 but that's no excuse. And she probably could use having her teeth done - they will be done in the spring :)]