Captives to the herdstones

 

Dacia Prime- Captured imperial citizens and soldiers were often brought by the beastmen insurgents to sacred sites known as herdstones.  There before the gods and select members of the herd they would be offered up by an Alpha Legion minor psycher to be inundated with the power of the warp as a sacrifice to serve the tribes and blessed children of the dark gods.

When this did not result in death it resulted in creating a powerful spawn that the beastmen insurgents could unleash in terror and shock attacks on imperial forces.