http://www.newsweek.com/red-dead-2-redemption-horse-guide-tips-bond-happy-1188487

Red Dead Redemption 2 is finally here! Now that you’ve finally started playing, you might have some questions about horses. Why doesn’t your horse go as fast as he could? Or suufers from low stamina? It’s because you haven’t improved your relationship with your horse. How do you make your horse happy in Red Dead 2? Don’t worry, reaching the fourth and final level of horse relationships is easy.

The better relationship you have with your horse, the better its stats will be Rockstar