Mark Gerard, 76, a respected veterinarian who cared for blue-blooded thoroughbreds but whose reputation was tarnished in 1978 when he was convicted on fraud charges related to an international horse-swapping scandal, died June 21 at a hospital in Miami after a stroke.

Dr. Gerard was a resident of Wellington, the seat of competitive polo in Florida, where he maintained a practice.

In the 1960s and 1970s, Dr. Gerard’s clients included Kelso, a five-time American Horse of the Year, and Secretariat, the 1973 Triple Crown winner.

“He was regarded as a top-of-the-line vet,” said Bill Nack, who wrote the 1975 book “Big Red of Meadow Stable: Secretariat, The Making of a Champion.” “He was very cautious and introspective.”

Supplementing his income as a veterinarian, Dr. Gerard imported thoroughbreds to the United States from South America.

Mark Gerard, 76, a respected veterinarian who emerged as the key figure in a horse-swap scheme in the 1970s, died June 21 at 76. (AP/AP)

In 1977, he bought two bay colts — with nearly identical white markings on their faces — during a trip to Uruguay.

One of the thoroughbreds was Cinzano, Uruguay’s Horse of the Year in 1976. The other was Lebon, a dud who had not won a race in months.

When the horses were imported to the United States, Dr. Gerard sold Cinzano to Joseph Taub, a wealthy computer executive. Dr. Gerard sold Lebon to Jack B. Morgan, a trainer. Both horses were stabled at Dr. Gerard’s farm on Long Island in Muttontown, N.Y.

Then, in a case that a judge said “might have been authored jointly by Alfred Hitchcock and Damon Runyon,” Dr. Gerard emerged as the key figure in a scheme that unfolded in the pages of newspapers across the country.

In June 1977, Dr. Gerard claimed that the champion Cinzano fractured his skull and had to be put down. The horse was reportedly buried in a Long Island landfill. Lloyd’s of London had insured the animal and paid out $150,000.

But in reality, the horse that died was Lebon.

Cinzano, alive and running, was from then on known as Lebon, and Dr. Gerard switched the two thoroughbreds’ official papers to reflect the change of identity.

Racing in late September, Cinzano (as Lebon) was a 57-1 long shot in a turf race at New York’s Belmont Park.

Dr. Gerard placed nearly $2,000 in bets on the horse. The thoroughbred won by four lengths.

When Dr. Gerard collected his $77,920 in winnings, the betting window attendants had to fetch extra cash from a safe.

Dr. Gerard walked away with the money stuffed in a brown paper bag, but the veterinarian’s big win aroused suspicion.

Later, a Uruguayan sportswriter saw a photo of the winning horse and recognized it to be the famous Cinzano — not Lebon.

After a formal investigation, Dr. Gerard was found guilty of misdemeanor charges of “fraudulent entries and practices in contests of speed.” He was fined $1,000 and spent eight months in jail in Nassau County, N.Y.

Mark Joel Geronimus was born Oct. 6, 1934, in Brooklyn, N.Y.

He was called Mike and he changed his last name to Gerard when he graduated from veterinary school at Cornell University, where he also played on the polo team.

He is survived by his wife of 41 years, Alice McCoy Gerard of Wellington; and a sister.

After the scandal, Cinzano was barred from racing at the highest levels. He was later purchased by Randolph Rouse of Arlington County.

Rouse was a fox hunter who rode Cinzano in Virginia point-to-point races. The pair were undefeated in 10 starts over a two-year period. Cinzano was a champion again.

“He was the best horse I ever had,” Rouse said in an interview. “Once the flag dropped, he took off in front. All you had to do was steer.”

Cinzano died in 1999 at 26 on Rouse’s farm in Aldie.