Some people look at the bloodlines and others the shape of the hoof, but no one knows exactly why some horses run better on the grass than the dirt. After a turf victory in her second start last fall, gray filly Frost Princess ran three times on the dirt at Pimlico and was soundly beaten each time.

After giving her a four-month rest, trainer Hamilton Smith returned Frost Princess to the races this spring with only one thing in mind for her -- grass racing. The filly, in her own way, thanked him, beating 11 horses in an allowance race on the turf May 5 and coming back Saturday afternoon to win the $50,000 Pearl Necklace for Maryland-bred 3-year-old fillies at Pimlico for the first stakes victory of her career.

Ridden by jockey Horacio Karamanos, who also excels on the grass, Frost Princess patiently allowed Cozy Gain to go by her in the stretch before launching her own rally and winning by 11/4 lengths. She ran the 11/16-mile race over a deep and yielding grass course in 1 minute 47.95 seconds.

"You can't go by the time," Smith said to Ron Kling, general manager for owner-breeder William Backer. "They were running in a bog out there."

Backer breeds horses at his Smitten Farm in The Plains, Va., but ships his mares to Kentucky, Maryland and West Virginia when it's time to foal to make them eligible for state-bred breeders' awards and stakes races.

Frost Princess's dam, Harvest Moon, was shipped to a farm in West Friendship, Md., 30 days before foaling, making Frost Princess eligible for the Pearl Necklace even though she was raised in Virginia.

Smith won the $200,000 Virginia Oaks at Colonial Downs last summer for Backer with the filly Art Fan. He would like to duplicate the feat with Frost Princess.

"I don't think we've seen the best of her," Smith said. "The next race is going to tell us what she's going to be."

Racing Note: Preakness winner Afleet Alex galloped 11/2 miles at Pimlico then boarded a van at 8:45 a.m. and rode up to Belmont Park, arriving at 4:30 p.m.

Record 9 Wins for Castro

Eddie Castro became the first jockey to ride nine winners at a track and tied the U.S. record for wins in a day Saturday at Calder Race Course.

Castro won nine races, including the $100,000 Office Queen Stakes aboard Snug Harbor, to break the mark shared by six jockeys, most recently Ken Shino at Fonner Park in April 2000. The 34-year-old from Panama also matched the mark of nine victories in a day set by Chris Antley, who rode four winners at Aqueduct and five at the Meadowlands in October 1987.

"I knew I was on a lot of live horses yesterday and today," Castro said. "But I never dreamed I'd win nine in one day. When you're on good horses you try to make the most of it. It takes some luck to win this many."

-- Associated Press