Grox

They look exactly as they sound like.

Grox are the primary livestock of the Imperium of Man and look pretty much like Grimdark Lizard Cows (there, a free awesome band name for you) or Morellatops from ARK. They're raised across countless number of worlds, because they can survive almost any environment, live on almost any plant food including driftwood and dead plants in soil, breed prolifically and (as a welcome deviation from the usual grimderp) are actually pretty damn tasty and nutritious. They're big (about 5 meters in length), agile and muscular. The only problem is that they're highly territorial, aggressive and generally need to be lobotomized to be wrangled, penned and bred. They also smell bad, but everything smells bad in the future. Also, your face'll probably end up ravaged by a carnifex at some point so it doesn't really matter.

Only War has rules for riding one as your "noble steed" in a cavalry regiment. /tg/ encourages this.

They are also mentioned offhand as existing in Ghur, the Realm of Beasts in Age of Sigmar. So that's neat!