Agricultural stocktaking can put you out (8,5)

I believe the answer is:

counting sheep

I'm a little stuck... Click here to teach me more about this clue!

'agricultural stocktaking' is the definition.
I don't know anything about this answer so I cannot tell whether this works.

'can put you out' is the wordplay.
I cannot quite see how this works, but
'can' could be 'tin' (both are metal containers) and 'tin' is present in the answer.
'you' could be 'u' (commonly used in online communication) and 'u' is present in the answer.
This may be the basis of the clue (or it may be nonsense).

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I've seen this clue in The Guardian.

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