Replacing cows on farm exposes a lot of problems (3,2,5)
I believe the answer is:
can of worms
'exposes a lot of problems' is the definition.
I know nothing about this answer so I cannot tell whether it can be defined by this definition.
'replacing cows on farm' is the wordplay.
'replacing' indicates an anagram (placing again).
'cows'+'on'+'farm'='cowsonfarm'
'cowsonfarm' anagrammed gives 'CAN OF WORMS'.
Can you help me to learn more?
(Other definitions for can of worms that I've seen before include "nasty problem" , "amateur angler's bait?" , "this may turn out awkward" , "Complex problem" , "Potential trouble" .)