The first step in deciding your dog's diet is to figure out if he truly is a "hardworking dog." If he spends most of the week indoors and then goes out for a vigorous run or long play session on the weekends, a normal diet will probably suffice, with maybe a little extra on exercise days to make up for the calories he'll burn off.
On the other hand, if your dog spends several days a week for the whole hunting season in the woods or in the water, or if your dog pulls a dogsled, dietary adjustments may be in order. Usually, you will want a nutritionally dense food with 27 percent protein and 1,850 digestible calories per pound.
Hardworking dogs often will need to be fed twice a day to keep up body condition. In addition, it is a good idea to keep handfuls of food with you when out in activity to give your dog a "pick-me-up" during the day. Some people feed their dogs candy to maintain energy and blood sugar. This can be dangerous because of the canine problems associated with large amounts of chocolate. Talk to your vet if you think you will need to give your dog a special boost.
Don't feed immediately before or after hard work. Make sure there is always plenty of water, but regulate it before and after exercise so your dog doesn't get sick. Keep the water cool, but not cold.
In cold weather, you may need to feed your dog extra just to keep warm. The rule of thumb is 7.5 percent more calories than normal for every drop of 10 degrees from normal.
One of the challenges for feeding working dogs is what to do in the off-season. There are two schools of thought: feed your dog less of the protein-dense food, which avoids a food transition but can leave your dog feeling hungry when the volume is reduced; or feed your dog the same amount of a less-dense food, which keeps the dog full but can result in finicky eating if the dog prefers one over the other. The best thing to do in either case is make the transition slowly over a two-week period.