At what size does a female Border Collie’s body mature?

A female Border Collie’s body matures at about 8 to 10 months, after which its size changes little. The 3 to 10 month period is rapid growth, needing scheduled, varied feeding for adequate nutrition.

Also, give growing Border Collies trace elements and calcium for healthy development. After 10 months, growth slows and nutritional needs drop.