Record domesticated animals rolling over grassy plain (6)
I believe the answer is:
steppe
'grassy plain' is the definition.
(I've seen this before)
'record domesticated animals rolling over' is the wordplay.
'record' becomes 'ep'.
'domesticated animals' becomes 'pets' (I've seen this before).
'rolling over' says the letters should be written in reverse.
'ep'+'pets'='eppets'
'eppets' back-to-front is 'STEPPE'.
(Other definitions for steppe that I've seen before include "crosses Siberia" , "Flat area of eastern Europe or Russia" , "Dry grassy plain of central Europe" , "Dry plain of Eurasia" , "Large area of unforested grassland" .)