Miniatures seem to be one of the poster breeds for insulin resistence; and that probably comes from their Shetland heritage and being able to thrive on sparse pasture; but, move them to an abundant, improved pasture and they are more likely to have an issue. not saying miniatures hroses can't graze, as many do, and many are out 24/7 without issue; but you gotta know the climate, forage and particular horse's needs. [I have pasture suitable for fattening cattle, not so great for keeping little horses looking like horses. so, my littles are limited; mostly limited to daylight hours (safety issue, as we do have coyotes, so they are in drylots at night).]