Picked up by the ears, number of cows, it's said (5)
I believe the answer is:
heard
'picked up' is the definition.
(hearing is a kind of picking up)
'number of cows it's said' is the wordplay.
'number of cows' becomes 'herd'.
'it's said' shows a homophone (sound like).
'herd' is a homophone of 'HEARD'.
'by the ears' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for heard that I've seen before include "Got to know (of)" , "Received aurally" , "Was told of" , "Caught - picked up" , "Perceived sound" .)