The 38-year-old Brooks hit each of his 10 dogs with a trail marking lathe, similar to a surveyor's stake, after two refused to get up and continue running on an ice field, race marshal Mark Nordman told The Associated Press from Nome on Sunday.
"He felt it was a discipline he needed to get his team off the ice," Nordman said.
Witnesses reported the incident to race officials. It happened Tuesday near Golovin, about 90 miles from the end of the 1,100-mile sled dog race in Nome.
"He lost his temper," Nordman said. "He spanked each dog on the team, just a real frustrating moment for him."
One of Brooks' dogs died the next day on the trail, between White Mountain and Safety, the last checkpoint before Nome.
Nordman said based on inconclusive necropsy results on Kate, a 3-year-old female, he has no reason to believe the two incidents were related. Further tests were being conducted.
An animal rights group was upset about the incident because it came when the dogs did not want to run.
"I'm sure they're exhausted and sick of the whole thing," said Lisa Wathne, a spokeswoman for People for the Ethical Treatment of Animals.
"When is enough going to be enough with this event? There is no way to do this humanely. No one who has any feelings for dogs should condone this event, or could possibly think it's acceptable."
Nordman said all allegations of dog abuse are investigated thoroughly.
"This behavior can't be condoned for any racer, any race, any event throughout the world," he said. "We can't have that."
Race spokesman Chas St. George said, "I think the process is the right thing, and what we have to do is like any year, is work more toward care and compassion for these athletes, I'm talking about the four-legged athletes."
Nordman said Brooks, who couldn't be reached for comment Sunday, was disappointed when informed of the disqualification from a three-member judge's panel.
"He just says he made a mistake and wants to learn from it, and become a better person," Nordman said, characterizing Brooks' reaction after contacting the musher Saturday night.
Brooks' disqualification is for this race only, and he could compete in the Iditarod again.
Jerry Riley, winner of the 1976 Iditarod, was banned for life from the race in 1990 after he dropped a dog in White Mountain without informing veterinarians the animal was injured. Nine years later, he was allowed back in the race.
Brooks finished 31st last year and was second in 2002 and 2003. Brooks, a former Yukon Quest International Sled Dog Race winner, comes from a family of renowned sprint mushers, including grandfather Gareth Wright and mother Roxie Wright.
Lance Mackey won this year's Iditarod, crossing the finish line Tuesday. Forty-six other mushers also have finished the race, 11 teams were still on the trail Sunday and 23 mushers scratched.
Two other dogs died in this year's race, one of pneumonia and the other from a hemorrhage due to a gastric ulcer.