A federal grand jury began hearing testimony yesterday in the investigation of switched identities of two thoroughbreds stabled in Maryland last spring.

Subpoenas of those who appeared today stated that the investigation "includes but is not limited to mail fraud and wire fraud."

Five persons who were served subpoenas by the FBI on Tuesday were questioned by Assistant U.S. Attorney Michael Schatzow regarding the mix-up of Dr. Peatoppy, a $12,500 claimer, and Sun Dandy, a $4,000 claimer.

Jockey Joseph Sierra, trainers Ed Coletti and Nate Heyman, Dr. Randy Brandon, a veterinarian, and James Rowan were asked about the case, in which Dr. Peatoppy raced three times under the name Sun Dandy at Bowie and Pimlico.

Rowan, who had worked as horse identifier, failed each of those times to notice that the horse's lip tattoo number did not match up with its papers. A substitute identifier picked up the switch on a fourth occasion, and the horse was scratched.

Trainer Ray Stifano then told stewards he had raced that horse previously as Sun Dandy. The identities apparently had been confused when both were shipped from then-owner Joseph Palladino's New Hampshire farm in January.

Although the race track investigation appeared to be over in April, FBI agents handed out subpoenas to personnel at Laurel and Delaware Park race tracks on Tuesday.

Brandon, who had treated both horses last winter, was questioned for about 45 minutes yesterday morning. "They want to look at some paperwork," he said, and indicated that he did not have with him the bills for working on both horses.

Sierra rode both horses for Stifano, and was queried for nearly two hours. "Mostly they wanted to know what we (Stifano and Sierra) talked about after (races)," he said. "A lot of questions about how the horse ran."

Heyman owned Dr. Peatoppy until last January when he was claimed for Palladino's stable. "I was asked how many times Joe (Sierra) got on him at the Meadowlands," he said. Sierra used to gallop horses for Heyman at that meeting, but both men agreed there was little chance Sierra would remember that particular animal.

Coletti, who twice saddled Peatoppy for Stifano, and Rowan were both asked to return for testimony next week.

Ivan Brown, who groomed both horses in question, also was subpoenaed and will appear Thursday. Stifano has not been subpoenaed, although he and a number of other race track personnel were closely questioned by FBI agents Tuesday.