i hold be told that frosty grass is not upright for laminates pony's but what whether they live out adjectives year?
yes grass in the winter is useless as it has no dry matter and is simply like water and no good to the animal and could build it ill. the animal needs hay or sileage which you can put out for the animal. also get some pellet to suplement the hay/sileage.
What causes the founder isnt being drizzling or dry. Its the nutritional content, winter grass have very little nutrition, hay does have a bit more, though the good point of either lays more in its roughage content. Its roughage that helps produce boil which keeps the animal warm.
Be very mindful of grain or pellets given to your pony, there lies the danger. If he is a chronic founder pony, after in spring fence him off most of the pasture until the spring growing surge is done so he cant pack up on rich grass. But a pony kept out all year is less likely to founder later one stalled or restricted from pasture.
You can find out more info on this online. My farrier is the one who initially told me about it, then I read some studies online. It's been a few years since after, and I no longer remember all the details, but the risk is frost on actively growing grass, not dead winter grass.
Hay is obedient because it really is just bulk and fibre, good for the digestion and make them feel full. A wedge of hay twice a day is apt to feed them to keep them occupied. It is no well-mannered witholding food from a pony, he will only find it from elsewhere.
Keep checking feet etc over the winter months for any signs of heat, mud-fever etc. In really snowy weather it is flawless to pick out hooves, brush them and then pack in motor grease to prevent balling up of snow which not only is discomfited for them, but can add muscle sprains to their injuries. And once feet and legs are clean and dry generously apply vaseline or similar to the heals and fetlocks to prevent mud-fever.