German Shepherds are large dogs with fast metabolisms when they are healthy, so it is important to maintain a regular feeding schedule with proper foods to maintain a healthy body weight. They can eat from 15 to 25 lbs. of dry food in a week, depending on their age and size. Feeding under this amount may lead to malnourishment while more may lead to obesity, especially if your German Shepherd does not get enough exercise. A healthy dog may at first seem slightly underweight - their ribs aren't visible, but can be felt, and their belly should be tucked in a bit at the waist
Determine the cause of your dog being underweight. Take your German Shepherd in for an examination by your veterinarian. It is possible you are just not feeding your dog enough each day, or perhaps you aren't giving them enough of the right kinds of foods. It is also possible they have a disease, infection, or injury that is causing them to lose weight. German Shepherds are prone to several illnesses that can cause a loss of appetite and weight loss.
Start a schedule of weekly "weigh-ins" to see if your German Shepherd is gaining weight, losing more weight, or staying at the same weight. This will help you determine if your weight gain plan is working or if you need to alter it. If you continue to see a lack of results, or if your dog continues losing weight even if you change feeding plans, you should take them back to the veterinarian.
Provide food several times a day. Some dog owners leave dry food available all day long and supplement that with wet food once or twice a day. If you do this make sure the dry food is high in protein and low in fillers such as ash and cornmeal. You can also give them dry food at several feeding times throughout the day. You may need to feed your German Shepherd three or four times to make sure they are getting enough food.
Offer fresh "people" foods with meals or as snacks. This does not mean give them leftovers from the table or scraps from the refrigerator. Give them vegetables, such as carrots and celery, as treats and bland cooked turkey and chicken as part of their meals. Lean meats, roughage, and unprocessed foods can help their digestive systems work properly.
Give them regular exercise. Walking, jogging, or swimming are activities that are muscle building and can be done every day. It is important that they are not just gaining weight through eating and getting fat. Building muscle mass is important to maintaining their proper weight and health.