how much food are you supposed to feed a yorkshire terrier puppy?

The dog food bag should give you the recommended amounts to feed him depending on his size/weight.
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1/4 cup. make sure you are using puppy food if your dog is under 2 years old
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For example, on the bag of Royal Canine food for Yorkshire's, there is a guide on the side of the bag to help determine the correct amount of food to feed. It's based on their age & weight.

http://www.petco.com/shop/product.aspx?sku=874817&cm_ven=nik&cm_cat=10&cm_pla=874817&cm_ite=5438362
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There is a "recommended serving" on all dog foods,check that out. Or,you can always ask a vet
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My puppy get's 3/4 a cup of food a day, she is a Yorkie and she is 4 months old. If you're not sure check with a vet.
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I feed a top-quality fresh-frozen raw diet and each yorkie gets approx. 2 TBSP per meal (that's twice per day after about 4-5 months). Many of these answers are more than I'd feed a mid-size dog, so I think the quality of the food must be terrible! Be sure to feed the best - it pays in the long run!
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Trainer, behaviourist, breeder, …