my dog is only 50lbs, she hiked for a month w/ me last summer before i sent her home, half-way through that month i switched her to puppy food, it has higher calories than regular dog food. so for your dog look for a puppy or working dog formula (hunting stores a resource for a working dog formula)

also i supplemented her food w/ zuke's power bones (at 50lbs she got 3-4 a day), which are 'endurance treats' www.zukes.com

this is the best article (in my opinion) for hiking w/ dog, it talks about food http://www.appalachiantrail.org/atf/cf/{D25B4747-42A3-4302-8D48-EF35C0B0D9F1}/fido.pdf