ANCHORAGE, Alaska — Lance Mackey is looking to make history again.

Last year, the throat cancer survivor became the first musher to win two grueling races back-to-back: the 1,000-mile Yukon Quest International Sled Dog Race and the 1,100-mile Iditarod Trail Sled Dog Race.

Less than two weeks after his fourth consecutive Quest victory, Mackey is looking to defend his championship in the Iditarod — with much of the same dog team.

"They're warmed up in my opinion and they're ready to race," said the 37-year-old Fairbanks resident, whose father and brother are past Iditarod winners.

Mackey is among six Iditarod champions in the 36th running of the world's longest sled dog race, which begins with an 11-mile ceremonial start in Anchorage on Saturday. The real competition begins Sunday in Willow, about 50 miles to the north. That is when mushers start chasing after this year's $875,000 purse, to be paid out among the top 30 finishers arriving in Nome, an old gold run town on Alaska's wind-swept western coast.

This year's event boasts a record field of 96 mushers, including 33 rookies. Organizers also are introducing a new tracking system that will let fans follow online the real-time progress of 20 top mushers. Officials hope to expand the system to all participants in future races.

Mackey, who will carry one of the tracking devices, is known for having superb dogs that seemingly can run forever, wagging their tails and barking at the finish line. He's quick to praise them as the real stars, all capable of leading the pack, the reason for his victories. So what does he feed these running machines with names like Larry, Hobo, Lippy, Handsome, Rev, Foster and Rapper?

"Rocket fuel," Mackey says with a laugh.

Competitive tensions are expected to be high, given the significant number of past winners and other strong contenders trying to prevent Mackey from repeating last year's feat.

"I think this race has the potential to be more of a thriller than any other race in Iditarod history," said Stan Hooley, executive director of the Iditarod Trail Committee. "One of the most exciting aspects for me is that there's room for the competition, and for the adventure for the person who does not expect to win the race but is looking for fulfillment of a lifelong dream."

The event also is expected to be closely watched for another reason: last year's suspension of a popular musher, Ramy Brooks, for abusing his dogs. Brooks, a two-time Iditarod runner-up, was disqualified from the 2007 race for striking his dogs with a quarter-inch-wide wooden trail marker. One of Brooks' dogs died the day after the incident, but a necropsy could not determine why it died. Race officials said there was no evidence that the musher was to blame. Two dogs from other teams also died in last year's race.

Animal welfare groups have long opposed the Iditarod, saying that winning, rather than the animals' well-being, is the top priority, underlined by the deaths of dogs most years. But the Humane Society of the United States, while not endorsing the race, is not actively campaigning against it. The organization is focused on other programs, said spokesman John Balzar.

"Three to four million dogs are euthanized in America in shelters every year for not having a home, 300 million farm animals are kept in cruel confinement and 75 million animals are killed for their fur alone," Balzar said. "The Iditarod and competitive dog mushing are not one of our programs."

Iditarod officials, mushers and other supporters say huge strides have been made in dog care, including the addition of volunteer veterinarians who monitor the dogs throughout the race. According to supporters, critics are wrong when they say the dogs are forced to run.

"No way we can make a dog go a thousand miles by being mean to it," Mackey said.

The Iditarod, begun in 1973, commemorates a run by sled dogs in 1925 to deliver lifesaving diphtheria serum to Nome.

The modern-day Iditarod trail crosses desolate tundra, thick forests and two mountain ranges along the frozen Yukon River, then goes along the dangerous sea ice up the Bering Sea shore to the finish line in Nome. Temperatures can plunge far below zero and winds can wipe out visibility for the teams.

"At some point in the race, things will be really bad. You can count on that," said Cliff Roberson, a Corvallis, Ore., neurosurgeon who last ran the Iditarod in 1995 and is now participating in his fourth race — a 60th birthday gift from his family. He expects it to be his final run to Nome.

"Not because of the dogs but because of me," Roberson said. "This event leaves everybody wiped. The problem is, the older you get, the longer it takes to recover."

On the Net:

www.iditarod.com