End user began originally to go after a cattle breed (8,5)
I believe the answer is:
aberdeen angus
'cattle breed' is the definition.
(I've seen this before)
'end user began originally to go after a' is the wordplay.
'originally' indicates anagramming the letters.
'to go after' says to put letters next to each other.
'end'+'user'+'began'='enduserbegan'
'enduserbegan' anagrammed gives 'berdeenangus'.
'berdeenangus' put after 'a' is 'ABERDEEN ANGUS'.
(Other definitions for aberdeen angus that I've seen before include "Type of cattle" , "Joint supplier" , "Scottish breed of cattle" , "Neat" , "Black, hornless breed of cattle" .)