Most of the 24 sled-dog teams that began the Yukon Quest on Feb. 6 have crossed the finish line in Whitehorse this week. Only two mushers have dropped out of the race, including Terry Williams, whose dog Bags collapsed and died on the trail Wednesday.

A sled dog belonging to an Alaskan musher has died — likely of a heart condition — while competing in this year's Yukon Quest International Sled Dog Race, the race's first dog death in three years.

Bags, an eight-year-old male dog belonging to Terry Williams of Fairbanks, Alaska, collapsed and died on the trail between the Pelly Crossing and Carmacks checkpoints on Wednesday, race marshal Hans Oettli told reporters Thursday in Whitehorse.

The 27th annual Yukon Quest is a 1,600-kilometre race through the rugged terrain between Fairbanks and Whitehorse.

Williams, a 37-year-old rookie musher, dropped out of the race at the Carmacks checkpoint, more than three-quarters of the way to the finish line, on Wednesday night.

Oettli said Williams was very upset about his dog's death because it felt like losing a member of his family.

When asked where Williams may be on Thursday, Oettli said he's not sure but that he likely needs time to himself

A website tracking Williams's progress had not been updated since Wednesday evening, when the musher was still on the trail to Carmacks.

Likely died of heart disease: vet

Yukon Quest head veterinarian Kathleen McGill said an initial examination indicates Bags died of heart disease.

"It appears to be cardiac and to be a silent cardiac disease, not one we picked up. There was no heart murmur," McGill said.

"All of the vet checks along the way indicated a healthy dog, eating well, well fleshed, well muscled."

McGill said the type of heart disease that killed Bags is rare in dogs, but further testing will indicate if her findings are correct.

She added that because of Bags's active lifestyle, he probably lived longer than he would have if he was not a sled dog.

Musher 'very caring'

Both Oettli and McGill said there was no indication that Bags was abused or neglected.

Oettli described Williams as a "very caring person [who] took extremely well care of his dog team."

"He definitely did not push the dog team," Oettli said. "That's why he's in the back pack [and did] … extremely well throughout the race. His dog team looked great."

It marks the first dog death in the Yukon Quest since 2007, when three dogs belonging to three different mushers died during the race.

Eighteen of the 24 mushers who started this year's Yukon Quest on Feb. 6 have crossed the finish line in Whitehorse.

As of Thursday afternoon, there were four mushers still on the trail. Yukon musher Gerry Willomitzer dropped out of the race over the weekend.