Illness, parasites or simple underfeeding could cause your dog to become underweight. If his bones are sticking out and he appears weak and lethargic, this means it is time to put on some doggy weight.
First things First
The evidence of food intolerance and intestinal obstruction can also be found, so your vet may prescribe amino acids and/or vitamin and mineral supplements for your skinny friend.
Feeding Tips
Try feeding your pooch 4 small meals a day. Add some healthy foods to his chow in order to encourage weight gain, while also adding a few spoonfuls of pasta or rice to supply the much needed carbohydrates.
Also, moist his food with low-salt chicken broth to make it more palatable, or add sauces or gravy made for dogs (make sure you don’t use sauces or gravy that have been cooked for humans as they are much too salty, sugary and spicy for canines).
RER
Calculate your dog’s Resting Energy Requirement (or RER) so you can determine his caloric needs. Small breeds (about 10 pounds) typically need about 450 calories; medium-sized breeds (45 to 70 pounds) need 1200 calories; while large dogs (over 85 pounds) need around 1800 calories per day.
If you have a giant-breed dog (weighing over 130 pounds) he will require about 2400 calories a day.