Reversing a trend of recent days, news Wednesday regarding Sunday’s Prix de l’Arc de Triomphe concerned horses being announced as participants in the race rather than defectors from it.

Chiefly, trainer Aidan O’Brien said that he would have two Arc runners, St Nicholas Abbey and Camelot, after putting both horses through workouts at his Ballydoyle training center in Ireland on Wednesday morning. St Nicholas Abbey, fifth in the 2011 Arc, had long been expected to start in the race. But the status of Camelot, who was denied the English Triple Crown when he finished second to unheralded Encke in the St. Leger Stakes on Sept. 15, came into focus only in recent days.

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O’Brien’s son Joseph is the only pilot Camelot has ever known, but O’Brien will ride St Nicholas Abbey on Sunday in Paris while Frankie Dettori has the mount on Camelot. As a 3-year-old, Camelot gets a break in the Arc weights that O’Brien, who is quite tall for a flat jockey, cannot take advantage of.

The services of Dettori, who has won the Arc three times, became available with the first notable Arc defection of the last week, that of Snow Fairy, who was injured during a workout on Sept. 28 and will not race again this year. Monday brought news that a case of swamp fever at the Cologne training center in Germany had put the local equine population in a 90-day quarantine that would bar defending Arc champion Danedream from leaving the yard of trainer Peter Schiergen and traveling to Paris. And on Tuesday, Nathaniel, who would have been among the Arc favorites, was taken out of consideration for the race after running a fever and showing signs of illness through blood tests.

That left 16 horses still in the Arc as of Wednesday’s entry stage, though supplemental entries, including that of French Derby winner Sanois, are expected Thursday. Heading the early Arc betting is the Japanese horse Orfevre, who had his final major exercise for the Arc on Wednesday at Chantilly, working one mile under race rider Christophe Soumillon. Orfevre has been stabled at Chantilly since mid-summer and won the Prix Foy at Longchamp last month in his Arc prep.

“We are very happy with his preparation,” Soumillon said after the work. “He seems in much better physical condition – more reactive – and his coat is beautiful.”