Massive size difference in littermates

I bred Millie (9.5 lbs) to Comet (10.5 pounds), and I got puppies with birthweights of 5.5 (Tanga), 6.5 (Junebug), 7 (Kali) and 6.5 (Cricket). With the exception of Tanga, you'd think all those puppies would grow to be about the same size. Not even close. At 12 weeks, Tanga was just over 4 pounds, and Kali was about 5. At 14 weeks, Junebug was 4.2 pounds and Cricket was 7 pounds on the nose. How the heck did two puppies with identical birthweights end up nearly 3 pounds apart at 3 1/2 months of age?

I understand how you feel. From the 4 puppies that I just had/have, there was only a .6oz difference between the biggest and smallest at birth and now at almost 9 weeks, there is a 2.1 pound difference between them.

Here are pictures of 2 girls from a litter I bought. When i looked at the girls as puppies they were fairly close in size and looked really nice. One quite growing Cowgirl, she tops off at 6 lbs when she is wet, her sister Maddie is appr. 11/12 pds between summer/winter weight.

Cowgirl:



Maddie: