13 ounces is a very dangerous weight for a puppy who isn't eating very well or much. They can expire, dehydrate in only a few hours. I would not care if I had to buy porterhouse steaks and feed him every hour, as long as he was gaining and growing. Once he has established a healthy weight and is use to eating enough at one meal to carry him over for another 3 hours, then he's on his way to being ok. It's going to take perseverance on your part to keep this baby alive and healthy. Dog food isn't going to do it right now, and you would never have to feed him dog food if you don't want. Science diet is one of the worst dog foods out there and usually all vets push this stuff for the profit. Most Vets. are NOT trained in neutrition. Real food is safer and healthier for him anyway. I have two Yorkies and two Chihuahuas that I feed only real food to and they are VERY healthy and happy. A really great book I use to help me take care of my dogs is Dr.Pitcairn's complete guide to NATURAL HEALTH for DOGS & CATS.
Here is some vital information for you:
http://www.prwatch.org/prwissues/1996Q1/madcow13.html
http://www.homevet.com/petcare/foodbook.html
http://www.api4animals.org/doc.asp?ID=79
http://www.nexusmagazine.com//Petfood.html
http://home.att.net/~wdcusick/03.html