Endlessly examine horses kept for breeding (4)
I believe the answer is:
stud
'kept for breeding' is the definition.
(I've seen this before)
'endlessly examine' is the wordplay.
'endlessly' means to remove the last letter.
'examine' becomes 'study' (synonyms).
'study' with its last letter removed is 'STUD'.
'horses' is the link.
I am not very happy about this link. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for stud that I've seen before include "Form of poker game" , "A horse breeding farm" , "Collar button or horse farm" , "kind of farm" , "Stallion; rivet" .)