Hi and welcome to YT! Yes, as Ann said..if he is acting like he has no energy, get him to a vet asap. Puppy Yorkies tend to get hypoglycemic and can go down hill super fast. Definitely keep some nutrical on hand (I always used to give it as a preventative thing...used it as a treat several times a day).
Feeding a pup? I believe in free feeding..I don't think you can over feed a puppy. Just leave food out and he'll eat when hungry. Otherwise, go by weight and what is recommended on the bag. At 13 weeks, I would definitely feed more than 2 times a day so he doesn't get hypoglycemic.
__________________ Terri, proud mom to Mandie  & Shelby-Dale  |