First of all, welcome to YorkieTalk, JenniferMarie!
PLEASE feed your little 12 week old baby 4 times a day, about a tablespoon at a time. They need to eat several times a day until they are about a year old. Best thing is to feed twice a day and then leave fresh dry kibble and clean water out for them to help themselves while you are gone. It's important for babies to eat several times a day so they don't have a problem with hypoglycemia, which can affect small breeds (it's a drop in blood sugar that can lead to unconciousness).
As to size, I think the formula is to double their weight at 12 weeks and that will be roughly where they will end up. So your little one should top off at around 8 pounds, just a really nice size for a small dog!
And just right to play with a Japanese Chin, too! Those are darling dogs! Keep visiting YorkieTalk and feel free to ask us anything. And post a picture of your little one, too. What is his name? We love furbabies here....we're like a bunch of doting aunties! |