Are they before or after chickens? (4)
I believe the answer is:
eggs
'are they before or after chickens?' is the definition.
(what came first - the chicken or the egg)
This is all the clue.
(Other definitions for eggs that I've seen before include "Oval food items" , "Contents of nests" , "Ova" , "Bacon and - -" , "Incites - farm produce" .)