I've been thinking since my first time being a brony, how do they turn their shoulders even in the show? Shoulders between a biped and a quadruped are very different, unless MLP ponies somehow have flexible shoulders.
The perverted part of me had to go and ruin this picture with the question: When they get older, where will their mammaries grow in, will that in the chest area like a human, or down near their 'hind' legs where ponies have them?
The writers have clarified the M6 are adults, so their mammary glands would be located near the hind legs. However they are entirely unnoticeable until the last few weeks of a pregnancy when they begin producing milk and swell. They return to the nearly flat size after a few months once the foal is grazing as well. As far as I know, only humans have permanently engorged mammary glands.