Can't recall if I replied to you last time - it rings a bell - but if you haven't already, I reckon about the best online sites to learn more about diet as it relates to metabolic/laminitic health are; Home
& Katy Watts | Safergrass.org
he has been on hay only. Twice a day.
Especially if he's 'prone to founder' I'd keep him on low nsc hay or grass & monitor his intake, but if twice a day leaves him going hungry for any period, that's not great. If you're thinking he can't afford more quantity but gorges his feed, a 'slow feeder' would be a good move, and if you're not sure how rich the hay is, it might be a good idea to soak it first, to leach out some of the sugars before feeding.
I would be including a good quality nutritional supp that will balance his diet. Be careful though, as 'ration balancers' & such can sometimes be grain based &/or sweetened. I'd also look into extra magnesium in the diet - google 'Magnesium For Horses' to learn more about that.
get him on a small amount of Safe Choice (I believe that's the correct name) for metabolic issues, and keep him on the twice a day hay feedings. Another friend suggested 3 times a day hay, no Safe Choice. And pull him out of the paddock because of the grass.
So he's got grazing 24/7? Then I wouldn't get too worried about the hay, unless of course you have rich grass & low NSC(or soaked) hay, so you want him to have more hay, less grass. As a new horse(I'd check his teeth & ensure he was effectively wormed too), I'd see how he goes on that first before adding anything else. If he doesn't start improving, then I'd probably consider a probiotic &/or ulcer treatment before adding feed too.
I wouldn't be inclined to choose 'safe choice' if you decide that he does need extra calories. Beet pulp, rice bran, copra meal & suchlike are the types of feeds I prefer for 'conditioning', because they're high in energy, low in sugar & high in fibre.
Oh and yes, stress is a big factor in laminitis & metabolic problems, so that shouldn't be discounted either.