You have to use context to convey "prey", and you wouldn't be able to simply say "We hunt for prey" in Dovahzul. That would be implied, though, in "We hunt" (Mu nir). 

Some examples:

"We knew the prey wasn't far." would be translated as "Mu mindok fin raan ni lost gut." (We knew the animal was not far) and this would implied that an animal (raan) is being hunted. To get "prey" across, you'd bring up hunting before this sentence. Something like "We didn't stop the hunt, because..." (Mu ni oblaan nir, fah...)

"The prey shook before lying there slain." might be "Fin nirlaan raan motaad us praan til kriin." (The hunted animal shook before lying there slain)