The story of Snowman, the plow horse that was rescued from the slaughterhouse by a Long Island trainer and transformed into a national show-jumping champion, has been the subject of many a magazine article and at least three books. So where’s the star-studded studio feature? Rights have reportedly been optioned by MGM, but for now, Ron Davis’ documentary “Harry & Snowman” is the only big-screen version.

The film’s human star is Harry de Leyer, a Dutch kid who married young and moved to America shortly after the end of World War II. As a horse-riding instructor at the Knox School in St. James, de Leyer went on a horse-buying trip to Pennsylvania. That’s where he spotted a gentle white horse just minutes away from becoming pet food. The taciturn Dutchman somehow connected with Snowman and purchased him for $80.

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That little story would become Snowman’s mass-media narrative as he went on to win local championships and then, in the late 1950s, the National Horse Show at Madison Square Garden. He won Horse of the Year twice in a row — the first to do so — turning both him and his owner into celebrities. Snowman had his own fan club; de Leyer went on Dick Cavett and “To Tell the Truth.”

“Harry & Snowman” is modest in scope and its research can feel a bit slender. For voices and sources, Davis doesn’t venture much beyond the de Leyer family (although with eight children to choose from, perhaps Davis felt he had plenty), and he doesn’t at all explain the esoteric world of show jumping. Davis gently probes de Leyer’s personal life — he was a stern father who tended to overshadow his children — but these details don’t much figure into the central drama.

Still, “Harry & Snowman” is a touching tale of an American immigrant and a working-class horse who together achieved success beyond their wildest dreams. Even now, more than 40 years after Snowman’s death, de Leyer can get emotional. Standing over Snowman’s grave, de Leyer says, “He made me.”