Some foundered horses cannot have grain, others have no problem with grain--we've acquired various foundered horses over the years, and each & every one of them has been given oats--we don't give huge quantities of oats, but they do get oats.
We've got one broodmare here now that foundered after a difficult foaling several years before we got her. She's nursing a foal now & is on 2nd cut alfalfa, with no problems whatsoever. Fresh green grass, though, would make her lame if she got much of it....small amounts do her no harm.
Thyro-L may help some foundered horses, though I wouldn't want to give it if the horse didn't test low on T4 tests....our Sherry foundered last year as a result of low thyroid, which was brought on by our iodine deficiency. She never foundered very bad, but she was quite sore at times. She was on Thyro-L for about 8 months; after 2 months on the medication her T4 level was up into the normaal range again, but we never noticed that the drug did too much for her otherwise. I had expected it would speed up her metabolism enough that she'd lose some weight & get over her lameness, but she did not. She has been off the Thyro-L for about 5 1/2 months now, and it was just 3 months ago that she started looking really good again; she dropped her extra weight and she started moving sound again. So, Thyro-L isn't a quick fix for all horses!!
Dona, I have to agree with Ashley & Marty--whatever caused those rings on your mare's foot isn't founder--there is something more than that going on with that hoof. For one thing, even if those were founder rings, they would be level, more or less, across the foot. In your picture, the rings are much higher on one side than the other, which indicates to me that the hoof is for some reason crooked. That outside wall is curling under--it isn't just the rings making it appear to be crooked. I tried to remove the rings, to see how the hoof would look without them, not sure how well this worked: edited to add--it didn't work; I smoothed out the hoof & saved it to photobucket, but the picture doesn't post here???? Anyway, without the rings, the hoof is still distorted.
How old is this mare?