(I’m using Velvet and Strap here because we know what they normally look like and I wanted to show how life under the changelings affects ponies)

Ponies that have been completely sucked dry of their love become low class workers that are mainly used for cleaning the hive and other menial tasks. Having to walk on jagged rocks most of the time leaves them unable to run away and mimics their superiors’ appearance in a grotesque way. They cannot exist outside the hive because they have forgotten what it means to be a free willed individual and will only live to serve the queen.

Husk ponies will often assist normal workers in transporting the queen’s eggs into breeding chambers, where those are placed into cocoons to grow into full-size changelings.

Sometimes husk ponies will forget what their assignment was or become more aware of their actual surroundings, at which point a normal worker will transform itself into someone they know and love and coax them back into doing their tasks.
In this case, Velvet’s “mom” would tell her to continue looking after her “little ones”.

If one can get a powerful mage to break the initial hypnosis spell and then apply intensive physical and mental care, it is possible to restore husks to their normal state. Subjects are not likely to fully trust anyone ever again though.