Since I have unlocked the final nest slot now, I changed my strategy to mostly giving xp companions to the females and pebble companions to the males, I keep one of every breeding unless there is something I want to keep "forever", then they will hit about level 5 by being adults or still be on level 1, I breed them and release the level 1 ones and keep training the level 5s to level 10, mostly with hunting and keeping the companions. For Zerdas I tend to give pebble companions in general since they are always needed for hunting quests and I don't get that many to keep them going.
Or in an easier to read way:
5 nest slots/litters per day
Keep 1 of each (unless Volmyr/Attribute I want, then keep out of the rotation)
Males - Pebble companion, release after breeding
Females - XP companion, release at level 10
Zerda - Pebble companion, release at level 10