Complex sentence: The Altai is a horse breed developed in the Altai Mountains, with hardiness that was significantly influenced by the harsh climate in which they were developed and the need for survival on only year-round pasture grazing.
Split into simpler sentences: The Altai is a horse breed developed in the Altai Mountains, and they have been significantly influenced by the harsh climate in which they were developed. This breed that was bred in the Altai Mountains is well adapted to its harsh climate, including the need for year-round pasture grazing.