"Vostroya is a world in the Halo Zone beyond the Eye of Terror, which swore allegiance to Mars during the Age of Strife. It is now ruled by a committee of Techtriarchs, a mix of Mechanicus Magos and more traditional Imperial planetary government. During the Horus Heresy, Vostroya refused to provide regiments to the Emperor, preferring instead to reserve the population in the manufactorium blanketing the world. After the Heresy came to an end the Vostroyans agreed to supply every first born son to service with the Imperial Guard."

Text from http://wh40k.lexicanum.com/wiki/Vos.....oyan_Firstborn

Dem fuzzy things