What condition were the dogs in when they arrived at Skagway from Dawson in The Call of the Wild by Jack London? Why?

In The Call of the Wild by Jack London, the dogs and their drivers arrived at Skagway after a thirty day trek from Dawson. They were exhausted and down in weight because they had not had a proper rest. Many were limping, and Dub had a hurt shoulder. All of them had sore feet from toiling day after day, hour after hour along the trail. 

In Skagway, the men expected a long stay-over to rest, both for them and the dogs, but it was not to be. Already Buck was down from his usual one hundred forty pounds to about one hundred fifteen, so when he and his mates were sold and expected to start up once again in only three days, they were not well rested and ready.