Hi em. Is your little shetland still suckling off his dam? At 5 months I would expect so but if not, then he will still need all the careful diet that you would draw up for a 5 month horse, but scaled RIGHT down to his tiny size, weight, metabolism. You will already know to take great care about the grass he's on because shetlands can swell up like barrage balloons almost overnight and next thing you've got laminitis. If it was me, I'd do a few things: ring a couple of feed helplines for advice; copy this post into Breeding; track down the number for the Shetland Pony Society and talk to someone there - they have terrific knowledge. If they aren't too far away you could call in and take pix of your foal for additional information. If your foal is on his own and not on grass, then he needs his tummy full of fibre just like a horse but, again, scaled down to his size and age.