Skinny pup

Question
Hello,

I bought my sister a puppy for xmas last year. He is a staffy cross blue heeler and around 5-6 months old. He had abit of problems with worms at the begining but I babysat him for about a week when my sister was away and when I gave him back he looked really healthy. I saw him the other day and he is very skinny. I ended up taking him home for the night to see if it was due to illness but he seemed to be eating and drinking fine, I fed him a few times throughout the day/evening as he has no energy and his stomach was still sunken in. By the time I fed him his dinner his belly looked like it actually had food in it so I didnt feed him again until the next morning. His ribs and spine are quite defined, he doesnt look like he has any muscle or fat on him. when he runs I can see his hip bones pretty well and when he sits his sternum sticks out. My sister says that she feeds him twice a day but I am concerned that she is under feeding him or lying to me. I also caught him eating his own poo aswell, though he only did it the once while he was with me. Could you please tell me what you think the problem could be? Thank you.

Answer
    You didn't mention if you gave him a dewormer when you had him or not. The majority of people who deworm puppies only buy dewormer that kills roundworms. So, even if you dewormed him, he might have another type of worm that was unaffected by that particular dewormer. If the dog has ever had fleas, I would suspect tapeworm. Tapeworm is spread primarily by fleas. Additionally, dewormers don't prevent worms, they only kill existing worms. Oftentimes dogs get reinfected, and the owners don't suspect worms because the dog has been recently dewormed. Evidence of roundworms and tapeworms can be seen in fresh feces, however, there are many other common parasites that cannot be seen by the naked eye in the feces. Just because you can't see them, doesn't mean he doesn't have them. Choose a broad-spectrum dewormer that covers tapeworm, roundworm, hookworm, and whipworm.
    Ask your sister to show you how much she feeds him at each feeding. If she fills his bowl, pour it into measuring cups to see how much he is getting. Double that number (since she feeds twice a day) to determine how much the puppy is being fed, and compare it to the feeding guidelines on the bag. Feeding guidelines on bags are often exaggerated, but if he is skinny he should be getting at least what the bag says. If he is eating more than the bag feeding guidelines suggest and is underweight, there is a problem. As always, I recommend feeding a high quality food (like Blue Buffalo, Wellness, Orijen, Earthborn, etc.) Stay away from foods with corn or corn products. Corn isn't necessity "bad" for all dogs, but companies add corn instead of meat because it's cheaper. Unfortunately, it is also a low quality protein and your dog has to take more energy to digest it, without getting as much nutrition from it. Additionally, the dog has to eat more to get enough nutrition, wasting even more calories in digestion. This is why feeding a $50/bag food can sometimes be less expensive in the long run than feeding a $20 bag of food. Don't trust commercials, the only way to tell if a food is good is to look at the ingredients on the bag. There are plenty of sites that will help you learn what to look for. My favorites are dogfoodscoop.com and dogfoodanalysis.com.
    Any time you are concerned with the well being of an animal, I advise you have it examined by a veterinarian. They are the only people qualified to diagnose your puppy. There's always the chance that the puppy could suffer from a metabolic disorder or other similar disease, which is something the veterinarian will have to test for. Good luck, hope that was of some help.