`When I was a child, I was always trying to figure out a way to get a horse. For years there was a contest run by a Kentucky tobacco company where you'd name a yearling, and if you named it correctly, you'd win it. Every year I named that yearling. But I never got anywhere with that and I never got anywhere with begging my family, so finally I decided that maybe I could find a unicorn. I knew that I was a virgin, and I knew that virgins could find unicorns, and I figured that, well, if it had a horn we'd do something about that when the time came. That's how desperate I was to have a horse."

The Pulitzer Prize-winning author, Jane Smiley, has come to Ireland to talk about horses. No, wait. She is on a book tour to promote her latest novel, and has dropped in to the Irish Writers' Festival to do a reading from that novel. But guess what the novel is called? That's right: Horse Heaven. And guess what it's about? Right again: racing.

But if you're thinking how perverse a subject this is for an established and highly-regarded writer, think again: with 19 horses of her own, it would be perverse if Jane Smiley didn't write a novel about horses.

Then again, Smiley's choice - and, more to the point, treatment - of subject matter has always been imaginative in the extreme. Her third novel, Duplicate Keys, looks like a murder mystery - is a murder mystery - but is also a shrewdly-observed study of human relationships. Her fifth novel, The Greenlanders, is a post-modern epic which recreates the world of the Icelandic sagas.

Her eighth novel, One Thou- sand Acres, a reworking of the King Lear story set in the American mid-west, was the one which won her the prize and the plaudits. But her 11th and most recent book, despite the apparent familiarity of its topic, pushes a few boundaries too. A huge, sprawling narrative whose overall looseness is reined in by the tautness of the individual strands within it, Horse Heaven merrily tests the limits of conventional story-telling while remaining a riveting read.

Is this interest in literary form the result of her time at the Iowa Writers' Workshop? "On the one hand," she says, "I went to Iowa but on the other hand I got my PhD in English with a speciality in medieval literature. If you're a medievalist and you're also doing Renaissance-type things, there are various forms - tragedy, comedy, romance - that are very distinct, and those interested me. And I was always interested in the different parts of a person's psyche that they appealed to. None of those parts in your psyche is excluded from the other part, so you can watch a tragedy and then read a realistic novel and then laugh at a comic novel. I liked the idea of being able to exercise all those parts of the writer's aesthetic brain."

The idea for Horse Heaven grew, she says, out of a conviction that here was a self-contained, teeming world that had been largely ignored by literature. "I was driving down the road in Wisconsin and I heard a sports commentator on the radio use a racing expression - `spit the bit'. And I thought, there's a whole language of horse racing that nobody has ever exploited.

"Most racing novels are about how Joe and his horse won the big race; but actually there's an entire world of horse racing that that's only a little bitty part of, because usually Joe and his horse don't win the big race - or any race at all. So I was interested in what everybody else was doing while Joe and his horse were trying to win the big race."

Did she worry that by choosing this subject, she'd lose a lot of readers who weren't interested in horses? She grins. "No. 'Coz I run around with people who are interested in horses all the time, so you begin to think that that's . . . " What everybody thinks? "Exactly."

Well, here's a reader who was never interested in horses, and who is cantering effortlessly though Horse Heaven, nodding happily as familiar horses loom into view; oh, here's that sweet little filly that everybody loves, or, oh-oh, this is the bad guy, or, dontcha just love this horse's sense of humour?

It's hard to explain how Smiley gets inside the horses' heads in the book - it's not by downplaying the human characters, or by resorting to a Mr Ed-the talking-horse superficiality - but she has the gift that all good writers have, of making you see the world differently for a while.

In this case, you get an occasional glimpse of the world through the eyes of a horse. "I guess the idea came naturally because when you work with horses, you're always confronted with the monolithic, impenetrable nature of their personalities," she says. "It's not like they're very malleable - they're trainable, up to a point, but pretty soon you have to ask yourself, well, why is he doing this, or why is she doing this? And then you start making up narratives that inevitably give the horse a point of view. And at that point, you're one step from writing a story or a novel."

Ultimately, the most interesting aspect of animals, even domestic animals such as horses, is their unknowability. "For example, we accept the fact that most male horses are geldings - that's just a given of horse life. But if you say, well, what does that mean for the horses, then it becomes an interesting question. Because it's a large population of a third sex.

"And there are actually many characteristics that geldings have, that mares and stallions don't. They're not only more amenable and docile, but they also have a kind of attachment to one another. Now, they're not becoming attached for reasons of reproduction, although there might be some remnant of that desire in there, but they become attached anyway. I wanted to investigate that idea: what does a gelding know about love?"

Jane Smiley's Horse Heaven is published by Faber & Faber