Based on the real-life 1973 Triple Crown winner, the film – which will hit theaters in October – stars Diane Lane as Penny Chenery, a wife and mother whose determination helped lead Secretariat to victory.
"She was a very savvy businesswoman," says Lane, 45, who to prepare for the role spent time with Chenery, now 88. John Malkovich plays Secretariat's trainer Lucien Lauren.
As for Lane's relationship with her equine costars, "each horse has its own personality," says the actress, who worked with several different horses in the role of Secretariat. "I had my favorite [horse], and mostly my relationship with the horse was a friendly one. He's in the top 10 of my costars, for sure!"
– Michelle Tauber
For more from Lane and photos from the film, pick up this week's issue of PEOPLE, on newsstands now