This is always a huge concern for me too because I am absolutely paranoid about founder.
We are told by the experts that horses should never be left without feed, that they should always have free access to hay when not on grass.
There is so much grass here this year because of all the rain we've had in the last 12 months (after 9 years of very little). And weeds.....weeds I've never seen before...some of which contain toxins that build up in the system and eventually damage the liver (if eaten).
I've been limiting grazing and putting the herd in a bare yard (I guess that's what you call a dry lot) between turnouts. They are going hours without feed which I know is not good but if they had free choice hay they would never stop eating.
They all seem to be doing OK but I worry about ulcers.
In fact when I think about it I seem to spend an awful lot of time worrying about the horses
and agonising about my management.
Pathetic, aren't I?
LOL! I don't think you need to worry about your horses getting ulcers as much as getting them yourself! I don't necessarily agree that a horse should have feed in front of them every hour of the day. What about show horses? Their feed is severely limited at times. Of course, a lot of show horses DO get ulcers!
I think a good rule of thumb is to never let a horse go four hours or more without food. They need a more constant supply of it going through their guts than other animals. And if they are out on pasture for four, five, six hours, and then brought off pasture, they don't need an entire bale of hay four hours later, either. Just enough that they can finish in a half hour is actually sufficient. As long as they get some more in another four hours.
I think every horse owner worries about founder, but I wonder what the statistics would show to be the actual number of horses that founder in a year? All my friends have horses. I've had horses for 40 years. I have NEVER had a case of founder, and never had a friend who had a horse founder. I know of only one other person in my area that had a foundered horse.
My horses get a big bunch of hay, individually in their stalls, each night around 7 PM and they don't get fed again till 7 AM. I know that hay we give them doesn't last 12 hours. Not if they are eating at it steadily. Maybe if they eat an hour here and then rest and then an hour there, it might last. I have no idea because I don't check them at 2 AM to see if they have any hay left, but they have always been just fine.