Summarize:

The B vitamins are mainly involved in enzyme systems that increase your dog’s appetite, and in energy metabolism of fats, proteins, and carbohydrates. In short, they ease the conversion of energy sources like fats, proteins and carbohydrates into energy, providing your pet the energy needed for growth and maintenance. The excess energy brought about by the increase in appetite and consumption will then be converted to fats and will prevent muscle catabolism, or wasting.  The best B-complex vitamins include Pet-Tabs® and LC-Vit®.  Be sure to follow the directions on the packaging. For puppies, it is recommended that you use liquid multivitamins like LC-Vit® (3ml daily). Another option is to bring your dog to a vet and have her given a shot of B-complex vitamins, if you do not have time to give it daily vitamin supplements. The regime is one injection, once a week for four weeks. If the dog's appetite has not improved at the end of this time, then further injections are unlikely to be beneficial. It is sensible to regularly deworm your dog because worms compete for food in the dog's bowel and cause poor body condition, silently sucking the nutrition out of your dog. Perversely, a dog with a heavy worm burden is likely to have a potbelly, but the bones of the ribs and hips lose fat cover and become stark.  Choose a broad spectrum de-wormer that can cover all types of worms. Praziquantel (Canex®) is a good example of a broad spectrum de-wormer.   Canex® for Medium Sized Dogs can be used at a dose of 1 tablet per 10 kilograms of body weight. Canex ® for Large Sized dogs can be used at a dose of 1 tablet per 20 kilograms of body weight. For smaller dogs, half a tablet of Canex® for Medium Sized dogs can be used. If it’s the first time that you will de-worm your dog, you can do it three times with a two week interval. From the first time on, de-worming can be done every six months to one year. Dogs that are active, working, lactating, frequently travelling, or getting used to a new home tend to become thin and lose appetite. You can give these dogs energy supplements that are packed with easily absorbed carbohydrates and vitamins. A good example of an energy supplement is Nutri-Plus Gel®. You can give your dog 1 to 2 teaspoons per 5 kg body weight or 10 centimeter (3.9 in) of gel per day (using the plastic gel applicator or doser provided).
Give your dog vitamin supplements. De-worm your dog with de-wormer medication. Give your dog energy supplements.