The grizzly bear can only breed if I also catch a boy grizzly. But along with "Supermum vs Grizzly in Arena", "Supermum, Grizzly Tamer" was #2 option. But another tempting idea I had, was to feed everyone's infants and children to the Grizzly, except supermum's, that way, she gets the honour she deserves (her first tyke actually has a material preference for candy, so I am partial to letting him live anyway), and I get rid of most the pesky children. Furthermore, I get to design a system for separating mothers from infants, and feeding the infants to a Grizzly Bear. Perhaps this would work:
A retracting bridge over a retracting bridge. Mothers are burrowed to top retracting bridge (or everyone is send there via military alert). Retracting bridge is opened, dropping everyone 1z onto lower retracting bridge, mothers drop their infants due to being stunned. Lower retracting bridge is NOT in burrow, so mothers can't collect their infants, and leave, leaving the infants stranded. Lower retracting bridge is opened, dropping infants into Grizzly pit. Grizzly eats infants. And this should probably take place within view of the meeting hall, so that everyone is suitably traumatized by the scene. Perhaps windows could surround the lower raising bridge, and all exits from the dining room could be cut off by other retracting bridges, so dwarves, terrified by the grizzly, nevertheless can't flee and are forced to watch it murder defenceless infants. Now I haven't tested the mechanics of this, but I think it should work, and it sounds like quite a good use for a wild grizzly bear and infants.