why my dog is losing so much weight?

Question
i have a german shepard mix/lab and he appears to be losing so much weight lately.  he still has good energy but i have noticed how much weight he has lost by looking at his bone structure.  what is wrong?

Answer
Age can have something to do with it but I don't know how old your dog is. Usually when a dog is losing an alarming amount of weight, for what ever reason, it warrants a trip to the vet's right away.

There are so many things this could be from- protein-losing enteropathy (which is usually accompanied by diarrhea), cancer,(which can be silent except for the weight loss) and a host of other problems.

You really need to get him into the vets. They should do some xrays to look for masses and blood work.
German Shepard's as a breed are prone to certain types of cancers as are labs and golden retrievers.

So a trip to the vet in imperative.
I hope that it isn't anything serious but please let me know when you find out what it is.