Ditto discussing grazing options with your vet, if he/she is coming out to do Spring shots/coggins soon
If your screen name is indicative of the breed you own, Tennessee Walkers are on the predisposed list for metabolic issues. Two of my three have that problem
Is your property cross-fenced to where it wouldn't be too difficult to make a dry lot area where they would still have access to shelter?
If not, my next thought would be to muzzle them until Spring grass is done "yahooing" it's fructose-laced self up thru the ground
I use the Tough-1 Easy Breath muzzles because they fit those big Walking Horse noses a lot better and give them a huge opening to breath. Saddles Tack Horse Supplies - ChickSaddlery.com Tough-1 Easy Breathe Grazing Muzzle <>
I was headed for three years with one horse's muzzle but he chewed the grazing hole to almost double the size and that is not a good thing - lollol
The mesh slow feed hay nets below the muzzle are also great and last a long time, in case you have a need for those
Also, there's clover in that field somewhere, even if it's only a small amount and might be a different type of clover than you're used to looking at:)
For some reason, nobody understands, my area ended up absolutely polluted with Hop Clover in 2011.
We had such a ground cover of it, that I threatened to set the entire barnyard on fire, once I realized what I was looking at. My regular hay guy didn't spray that year and I ended up throwing out around 70 bales of hay because it was so polluted with hop clover.
I didn't see it in the pasture because the horses kept it eaten down. I have 22 acres but that year I noticed they spent all their time in just a few areas, eating clear down to the dirt. I finally figured out that must have been where the hop clover was:(