Nitrogen in a work at Keeneland. (Courtney Snow/Past The Wire)
Breeders’ Cup Closer Look
There are moments in racing that seem almost scripted — the underdog story, the perfect pairing of horse and trainer, the glint of destiny that turns into dominance. For trainer Mark Casse and Nitrogen, the story began humbly, with a hunch, and has now arrived at the Breeders’ Cup World Championships, where the filly stands among the leading contenders for the Longines Breeders’ Cup Distaff (G1).
“This seldom happens,” Casse said. “It’s nice, you know. I look back — it’s crazy how things happen. She was on the AE (last year); she wasn’t even in. We weren’t sure, but we shipped her out here, and she ended up getting in.”
Last year, Nitrogen was a late addition to the Breeders’ Cup Juvenile Fillies Turf (G1), only drawing into the field after another horse scratched. “(Jockey) Jose Ortiz’s horse was the one, I believe, that scratched that let us draw in,” Casse said. “And then he rode her. She had a really tough trip. We kind of got shut off, and she dropped back — but she came running. I felt after that, if she had had a little better trip, she could have given the winner a run for her money.”
That race hinted at what was to come. The filly who nearly missed her Breeders’ Cup debut has since become one of the sport’s most versatile and intriguing stars — a turf talent who made a seamless, and stunning, transition to dirt.
“She’s done well and then, of course, the transfer to dirt — it’s just been amazing,” Casse said. “It was a race that was supposed to be on the turf that came off, but she won so impressively. When you looked at her numbers… she ran her best on the grass as a seven, then a one on the dirt. Her dirt is so much better than her grass. And her grass is pretty good.”
For Jon Green, who manages D.J. Stable with his father Leonard, Nitrogen has continually exceeded expectations.
“With a filly like Nitrogen, I shouldn’t be surprised anymore with what she’s accomplished,” said Green. “Really, from the beginning of her training, we’ve always felt very highly of her. We ran her against the boys first time out. We ran her as a maiden in two Grade 1 races, and we just always had a good feeling about her.”
The decision to put her on dirt, Green admitted, was one of the toughest calls they’ve ever made.
“That was one of the most difficult decisions that we’ve had to make in all the years we’ve been in the business,” he said. “We were taking basically the top 3-year-old turf filly in the country and running the risk of damaging her by running her on a surface that she’d never run on before. So, it was a little daunting. But, just like everything else that she’s done in her career, she not only won, but in a very impressive fashion. The rest has been history.”
History that began, fittingly, with instinct. After Wonder Wheel earned her Eclipse Award, the Greens invited Casse to choose one homebred yearling to keep — the rest would be sold.
“We’re really excited about Nitrogen,” Green said. “Mark looked them all over and chose her. He said, ‘Don’t sell her. She’s the one. I want to use my ‘get out of jail free’ card on her. This filly breathes different air.’ That’s how she got her name and why we named her Nitrogen.”
NITROGEN, a multiple graded stakes winner on both turf and dirt, looking gorgeous as always galloping this morning at DMR ahead of Saturday's @BreedersCup Distaff!
— Equibase (@Equibase) October 28, 2025
Last time out, she finished 2nd by a head to fellow Distaff contender Gin Gin in the G1 Spinster Stakes at… pic.twitter.com/iFY9z11I6P
Casse smiled at the memory. “They had like 20 or so,” he said. “Wonder Wheel had done very well, and they said, ‘You get to pick one.’ And that’s who I picked. She was beautiful. You’d have a tough time finding a prettier horse. When we were breaking her, I kept saying, ‘I hope this one’s good — because I picked this one.’”
That faith — and partnership — has carried both trainer and owners to new heights. D.J. Stable is in the midst of a career year, ranking fourth nationally through Oct. 27 with 48 wins and nearly $4.4 million in earnings.
“I think partnering up with Mark Casse and his team has brought us to a new level as a racing operation,” Green said. “We’ve had success in the past — we won Grade 1 races and the Breeders’ Cup (Juvenile Fillies) with Jaywalk before winning it with Mark and Wonder Wheel. But overall, our racing operation had kind of not gotten through the glass ceiling we anticipated. From the first moment we started talking to Mark, we realized that he was more than a trainer — he’s a great communicator, and he’s an entrepreneur. I can’t say enough about our relationship with Mark, personally and professionally.”
