Here's the link to the "Life Design". Nutrena: Products - Horses - Life Design® - NEW Life Design® Senior
There should be Guaranteed Analysis information somewhere on the bag of feed. It will either be printed right on the bag or be on a tag that's been sewn to the bag.
Look to see what other ingredients are in the feed.
The first three listed ingredients are the major components; everything else is found in trace amounts.
Looking at this link it looks pretty good.
Increased energy can come in two forms:
1. She's feeling really good because the feed is working.
2. It can be a jittery/spooky kind of energy because the horse has an intolerance to something in the feed.
2.1 Also watch to see if she's becoming nippy, kicky, starting to pin her ears a lot, swish her tail in aggravation. If she were to start doing these things, when she didn't do them before going on the new feed, she's got a food intolerance to something in the feed.
One of my TWH's is oat/corn/soy intolerant. I haven't needed the riding crop in the bath bucket since I took him off oats/corn/soy four years ago. He's also got dust/mold/pollen allergies -- he's a train wreck - lol
I also cannot give this TWH or the other teenager more than a handful of timothy/alfalfa cubes sprinkled over their supplements or they will get testy.
My two mid-20's guys eat 3# - 5# of soaked cubes every day and they're fine; they need the extra protein and amino acids to keep their muscles toned. There was a point in their youth that they would've both been climbing the walls if I'd fed that much alfalfa - even mixed with timothy
My point is to monitor what form
the mare's energy level takes on.
If it's a "meat and potatoes-I-feel-good!" don't worry about her and enjoy the ride
If it's a "Hi-C and a-dozen Hershey-bars-jittery" kind of energy, you'll need to see what-all is in the Nutrena, then find something else that doesn't have the same ingredients.
I hope that all made sense