Some histories say that when the Ur-Quan first entered this sector of space, the Ilwrath had not yet developed hyperspace capable engines, and their early conquest was much to their delight, as the Ur-Quan provided them with the hyperspace technology allowing them to practice their unholy rituals on many other races during the war.
The Ur-Quan later reveal that the Ilwrath were the strongest and most reliable of the Hierarchy battle thralls, and that their destruction with the Thraddash was perhaps the biggest defeat the Battlethralls had ever suffered. (SC3)
"Upon emerging from the egg sac, the Ilwrath hatchling participates in what is known as the Birth Rite. Each hatchling competes with its siblings for its first feeding of blood, and a large number of hatchings perish during this event. Whether the blood was part of the natural diet of the Ilwrath before the establishment of the worship of their gods Dogar and Kazon is unknown."
I'm pretty sure the relevant lines from the Ilwrath actually referred to cannibalism among the hatchlings; the "first frothy draught of blood" being the blood of their siblings.
"Ah, Our Culture Is Rich With Meaningful Tradition. During The Birth Rite The Egg Sac Teems With Many New Potential Deaths The Hatchlings Fight Over Their First Frothy Draught Of Blood. In The Ensuing Frenzy, Many Hatchlings Are Consumed, Either Partially Or In Their Entirety."
"Hu-Man, You Do Not Understand. It Is As It Has Always Been. When The Hatchlings Struggle From The Egg Sac They Show Their Respect To The Twin Gods Of Death During Their First Frenzied Gorging. From That Moment On, The Directives And Philosophies Of Dogar And Kazon Are Manifested By The Hatchling."