I'm not a breeder, but I just had to chime in with my recent experience.
I use a veterinary hospital, so I can see one of 5 different vets depending on their rotation schedule (I have one that I really respect and that I request specifically for illness/injuries).
Anyway, when I took Colby Tate in for his first vet visit the doctor looked him over and said (without my asking or prompting in any way) that Tater would probably be at least 9 pounds.
I just smiled and nodded, as Colby was so tiny and has such tiny bone structure even an idiot could tell he was gonna be a tiny.
On the next vet visit we had a different doctor. She said (again with no prompting from me) that she doubted he would make it to 3 pounds (he was only 3 ounces under three pounds at the time!). Little Tater is now almost 6 months and weighs about 3 1/2 pounds. I don't think most vets really have a clue on how to estimate adult sizes.
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He is your friend, your partner, your defender, your dog. You are his life, his love, his leader. He will be yours, faithful and true, to the last beat of his heart. You owe it to him to be worthy of such devotion. -- Author Unknown