There are so few unique horses in vanilla Skyrim that you can count them on one hand. Shadowmere is obtained via the Dark Brotherhood and Frost is found through a questline in Riften, while Arvak can only be acquired after downloading the Dawnguard DLC. The options are lacking, to say the least, which is where Skyrim Anniversary Edition comes in.
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Skyrim Anniversary Edition adds three new unique horses and seven tamable wild horses,
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