Too hard to tell at that age. I think Jackson is a Silky and so does a few Silky breeders who I've talked to. However, it's not impossible that he's just a badly-bred Yorkie, and in fact is probably more likely considering they are a lot more common.
Size isn't the only factor though. I've seen some very small Silky's and very large Yorkies. I think Jackson is very Silky in his eyes, his ears, his muzzle, his body length, etc. Which is stuff you will be able to see more as he gets older.
He's ADORABLE! |