Why is Orion referred to as Darkseid's Firstborn?

Why is orion referred to darkseid's firstborn son? I thought Kalibak was the eldest son....

Here are links that identify orion as firstborn

http://www.killermovies.com/forums/showthread.php?s=&threadid=471442&highlight=mister+miracle+powerful

http://www.dccomics.com/dcu/heroes_and_villains/?hv=origin_stories/darkseid&p=2

http://www.killermovies.com/forums/f95/t346614.html

use that, or one of our New Gods threads. thanks.