I know this is late posting, but been off with school and work and not really been able to read. Toxic poisoning will do the back feet and it acts like founder in that the horse will react the same. Very high fever was the case in my stallion when he had it, we were in a drought situation and according to A&M the plants that are mildly toxic become more so with the drought. He ate some evening shade down on the creek, which is the common name here, but others call it something else...I found him where he could not walk, just like founder except it had set up in back feet. Swollen and fever...I hit him with high pressure water and it did leave his feet with rings and one of the heels on the left hind was a slight contracted. It had affected his kidneys, we were lucky and he was okay, and still rideable, but his feet in the back did have the rings. Now with fever it will leave rings as well. I been told also if your horse goes through a drought it will tell the tale in the rings on their hooves, even with the best nutrition.
Maybe a little late to help you Rainie..but, just something I had lived through with my horse.
Easty
