Tordenskyen (1945) [DVD] Movie

The son of a horse rancher (Preston S. Foster), McDowell takes it upon himself to train Thunderhead, a white colt with the same rebellious streak that distinguished its mother (Flicka). Thunderhead helps McDowell round up several horses that had been stolen from his father, and also attracts the attention of a racing aficionado (Ralph Sanford). Once fully grown, Thunderhead indicates that he'd be happier running wild, so McDowell tearfully but proudly gives the horse his freedom.