When Channing first rides the zebra around the track, her braid appears to be very long down her back. In other scenes her braid is not that long.
When Sir Trenton first sees his son racing Stripes, his owner/carer has just started to undo his rug and does not appear to undo the front two straps. When he rears, the front two straps appear to be undone as the rug slips straight off his body.
As Nolan Walsh comes around the turn of his newly made corn field track and climbs off his tractor, there are no corn stalks on the ground. In the far shot of Channing hugging him, the ground is littered with stalks.
While Trenton's Pride is a foal, his blaze doesn't reach all of the way down to his muzzle. When he is grown up, it is past his muzzle. Horses' markings don't change that dramatically.
A zebra's stripes are like fingerprints - no two are alike. In the montage of Channing training Stripes you can clearly see she is riding different zebras at different times.
Every so often through out the movie, Stripes' head is very hairy and you can see the black dye or paint on his face. It isn't as dark as his normal color. The next clip, his hair is very short and dark black, with his normal wide stripes again.
"Sir Trenton" shown running after his son, is a gelding.
After Channing got out of the car after arguing with her dad, she clicks to Stripes who makes a cantering hoofbeat sound, but when viewed, Stripes is still trotting, then canters.