If you know your horse and most of the other stuff like: pacing up and down hills, electrolyting, when your horse is tried and other little signs of "just-not-right." Then I'd say, ride a slower 50 and go step by step in doing so. You gotta start sometime. A fifty is not just 2 25's, things change out there in the second 25. Weather, dehydration, fatigue, etc.
Just make sure you have learned most of your horses health issues. Then go have a good long, fun trail ride!
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