Pip I have noticed over the yrs the decline in the quality of bitches in N S & Nuttal lines. I have spoken to a few good digging men who keep these lines and most said the same. THEY CANT GET DECENT STRONG DIGGING BITCHES FROM THESE LINES. Over the yrs I have bred good strong dogs but never get strong bitchs most come small, and very few make 100%. WHY SHOULD THAT BE.
If you breed tight for long enough, the females size will decrease.
A friend has racing pigeons and by breeding close he can get the cock birds nigh on perfect, peas in a pod. But the hens get smaller & smaller ea