Dogs can become underweight for a variety of reasons. Just as with humans, it's important that your dog stays at a good, stable weight. Otherwise, your dog could suffer from a variety of illnesses. For a dog that is a picky eater or just can't seem to gain weight, there are several different methods you can try to put a few pounds on it. If none of them work within two to three weeks, you must take your dog to a vet.
Put your dog on a puppy food diet. Since puppy food is meant for adolescent dogs, it is full of vitamins and nutrients that are meant to cause weight gain in the dog. Give your dog 1-2 cups of puppy food two to three times a day. Exactly how much you give will depend on the size of your dog and how much weight you are hoping to put on your dog.
Mix a canned dog food along with your dog's dry food. These canned foods are often more appetizing to dogs. Mixing the canned food along with the dry food will serve as a "two in one" meal for your dog. Make sure that the dry food is fully saturated with the canned food before you serve the food to your dog. You can also use two cans of food per meal if you want your dog to gain a larger amount of weight.
Give your dog peanut butter. Peanut butter is a food that is high in protein, calories and fat and should put weight on your dog in no time. You can mix peanut butter along with dry food as a way to get your dog to eat an entire meal. You can also scoop out a tablespoon of peanut butter and let your dog lick the peanut butter off. If you choose to give peanut butter as a snack, you can give your dog 1-2 tablespoons of peanut butter three to four times a day.
Add a supplement to your dog's food. Food supplements are very high in calories, minerals and vitamins. Dogs also like the taste of the supplement, thus causing the dog to eat the dry food that is mixed along with the paste or gel. These gels can be obtained online (see Resources below), at a vet's office or a pet store.
Try giving your dog "satin balls." Satin balls are a mixture of different foods that are then moulded into spheres, much like meatballs. The ingredients in the satin balls are meant to put weight on a dog in less than two weeks. See the Resources section below for more information about how to make satin balls as the ingredients do vary based upon the size of your dog.
Remember to give your dog plenty of exercise when attempting to put weight on the dog. You don't want to dog to simply gain fat.
Consult your vet before you attempt to put weight on your dog. This is to make sure that your dog does in fact need to gain weight. You should also consult your vet if you notice your dog losing weight rapidly as this could be a sign of a serious disease.