Over Christmas dinner, I had a 'spirited' conversation with my brother about domestic animals: horses, cows, dogs, the usual.

I'm a vegetarian who'd, given the chance, rather spend my time with animals, and he's vegan and in the most stubborn phase of undergrad rhetoric: domesticating animals is slavery, he said (or words to that effect), and they should all be set free. I argued that, as the inheritors of a contract, if you like, that was drawn up thousands of years ago, it would be a dereliction of our duty and responsibility to them. In the end we agreed to disagree.

I'd like to show him - and everyone - Buck, for this wonderful documentary is the perfect illustration of what can happen when the relationship between humans and animals is done right.

At first, Buck Brannaman seems like any other renaissance cowboy: he's softly spoken, has a knack for casual eloquence, and runs four-day workshops to help people with troublesome young horses. I mean, we've all seen The Horse Whisperer, right?

Well, as it turns out, Brannaman is the horse whisperer (he was part of the book's inspiration, and served as an advisor and riding double to director and star Robert Redford, who appears in this documentary).

A protegee of the inventors of "natural horsemanship", Ray Hunt and Tom Dorrance, Brannaman teaches "starting" of colts, as opposed to the "breaking" methods familiar to most ranchers (old footage of spirited young horses being broken is shown and it's nearly unwatchable in its brutality). He waves airy little flags at them - there are no whips - and stresses gentle, affectionate treatment. "Just love on him", is a frequently used phrase in his workshops.

Watching these naughty little colts suddenly become calm and graceful, and watching Brannaman and others move balletically through fields as though the horse's legs were their own, would be enough gee-whiz documentary material in itself. "Everything you do with a horse is a dance," he tells a crowd. 

But director Cindy Meehl gradually weaves in threads of Brannaman's own story, making his present gentleness even more remarkable: a child star, along with his brother (who is absent from the film, which would be frustrating were the end result less satisfying), he toured the rodeo circuits doing blindfolded rope tricks. Behind the scenes, the two little boys were beaten unmercifully by their strict, hard-drinking father Ace.

The more you learn about his background, the more his work with horses makes sense: he knows what it is to be young and frightened. As he often reminds his workshop attendees, the horses "are just babies". He also knows that an early life of violence does not have to beget a lifetime of it. It makes the man he is today even more remarkable.

Meehl's first film, Buck has a relaxed pace that occasionally slips into shambling, but the compelling nature of Buck's story - and his work - overcome any narrative weaknesses.

(It's not all dreamy Zen horsemanship, either - in one terrifying sequence, a woman brings an aggressive, possibly brain-damaged colt to a workshop, testing Brannaman's skills considerably.)

This is a lovely film, and one that will no doubt have repercussions in many aspects of the viewer's life. As Brannaman notes, people take things away from his workshops that affect their relationships, their work, and, most movingly, their art. In his world, horsemanship can become art, as some beautiful shots of horses and riders soft-shoeing their way around the arena demonstrate.

In many ways it's a perfect companion piece to The Black Stallion; this documentary has a similarly meditative pace to Carroll Ballard's exquisite work of fiction, in which the connection between horse and boy was triumphant due to its distinct lack of "traditional" training methods, with its wordless moments of horse and boy moving in silent, joyful unison.

(They're also both films that had me in floods of tears from beginning to end.)

A must-see even for those who are not cut from the "OMG ponies" cloth, Buck is the sort of film that quietly restores your faith in humanity's potential for great kindness.

- five stars

Buck is in selected cinemas from February 16th.