Image imported from derpibooru 
Original Description:
 
This is an example pic of height difference between the avg broodmother and the pygmy broodmother. Pygmies are the same age as broodmothers but take on a shortstack build, have one less finger on their claws and slightly bigger ears, they are known to be alot more docile and less erratic during breeding. Pygmies are the only ones to have hooves for feet, unlike the broodmother’s stubby feet or hoof combo [Broodmothers can have hooves or stubby feet, just a rarity to have both.]  
Pygmies are mostly known to stay in groups to feel safer, they let out smaller roars than the normal types and can be pet.
 
Examples of pygmies: Applebloom, Sweetiebelle, Scootaloo, and other smaller species.