Desormeaux failed a Breathalyzer test at Belmont Park in New York on Friday and was removed from his three mounts on the program, according to officials at Pimlico Race Course, site of the Preakness.
"It was a team decision," Tiger Walk trainer Ignacio Correas IV said of the switch to Dominguez, who was voted the nation's outstanding jockey the last two years. "Ramon is a great rider. We're happy to have him."
The Daily Racing Form said on its website that the test showed Desormeaux had a blood-alcohol level of .05 per cent or higher, which constitutes "alcoholic impairment."
A rule that went into effect last month in New York requires that jockeys named to ride undergo an alcohol test.
In a phone interview Friday with Daily Racing Form, Desormeaux said he had "a little too much wine with dinner last night" but had stopped drinking by 8:30pm, knowing that he would have to take a Breathalyzer test.
"I guess my body doesn't deal with it the way your body does," said Desormeaux, a 42-year-old two-time Preakness winner and three-time champion of America's most celebrated race, the Kentucky Derby.
Desormeaux has not been suspended, although the New York State Racing and Wagering Board is conducting an investigation.
He was eligible to run in the Preakness but Tiger Walk's connections decided it was best to go with Dominguez.
Tiger Walk, a Kentucky-bred colt who finished fourth in the Wood Memorial in his last start with John Velazquez in the saddle, was listed at 30-1 odds in the morning line.
"I'm excited to ride the horse, not necessarily the way it happened, Dominguez said.
"I'm happy that they chose me to ride this horse. I know very little (about him).
"I rode against him a couple of times in New York, and I will have to go look at a couple of replays to take a look at his running style."
Dominguez, 35, has ridden in the Preakness nine times previously, failing to win but finishing second aboard Scrappy T in 2005 and First Dude in 2010.
Bodemeister was the early favourite for the Preakness at 8-5 odds, while Kentucky Derby champion I'll Have Another was the second choice at 5-2.