[Nintendo DS] [200?] Horse Game

Yeah I know horse games were and are a dime a dozen and I played loads of them growing up. But I'm trying to find this one specifically.

I remember various details about it. It was for the original Nintendo DS, the graphics were either 64-bit or higher, in overworld navigation huge white arrows pointed at buildings and the arrow would be yellow if it was a story quest location.

The story involved racing horses in competitions as well as open locations for fun. Each open riding area had several exits which would lead to new areas and the climax of the story required the player to ride and explore until they discovered the Hidden Valley (or a similar name) with a secret legendary herd of wild horses and then win the final racing competition with the herd's leader.

The only other helpful detail I can remember is that I was able to play the whole thing within a day so it was a short game.

Sorry I can't be any more helpful but I hope this is enough to help track this game down.