From Fuze's Blog of Stuff:

A Look into Other Methods of Harvesting — Mana Farming

This method is the most advantageous to the changeling, but worse for the magical beings turned livestock. Similar to the catch and release method, this removes the release step. Magical creatures are captured and held captive indefinitely to be used solely as mana batteries in a way. Most commonly kept in cocoons so that a steady stream of mana is continously infusing into the ectoplasm, creatures can also be locked up in chains or mind controled to have mana extracted the conventional way. Even further, creatures can be bred to increase the stock. A controversial method certainly, as it can be quite cruel to the magical creatures subjected to this treatment.

Chrysalis seems to have collected an unfortunate pony to extract mana from using the cocoon method. Rebuilding a hive will take some large mana reserves after all.

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Now for the other extreme of the spectrum, changelings like Chrysalis, who merely view other races like food/livestock. She cares about her hive much more than she cares about races other than changelings, so shes not against abducting ponies. Also, I have very little experience drawing females, go figure.