If you and your Chihuahua decided to move to Alaska, you would take precautions. You'd buy him a sweater...maybe a heated pet bed. Why? Because a tiny, hairless native of Mexico is not built for the tundra.
The same is true for horses. Some breeds developed in desert-like conditions with very sparse grazing. Lush, abundant pasture may seem like horse-heaven on earth, but in truth, some of these horses may founder or colic more than other breeds better accustomed to these conditions.
If your horse seems to suffer from mysterious bouts of founder or colic, think about where the breed evolved. Arid? Swampy? Hot? Cold? You may need to make some adjustments to her environment to more closely imitate her ancestral home.