Starts to round up ruminants at large in the countryside (5)
I believe the answer is:
rural
'in the countryside' is the definition.
(I've seen this before)
'starts to round up ruminants at large' is the wordplay.
'starts to' indicates taking the first letters.
The initial letters of 'round up ruminants at large' is 'RURAL'.
(Other definitions for rural that I've seen before include "Old country fellow" , "Rustic" , "Pastoral or agricultural" , "Sort of dean" , "Countrylike" .)