American uncle raised backward cats (5)
I believe the answer is:
pumas
'cats' is the definition.
(puma is a kind of cat)
'american uncle raised backward' is the wordplay.
'american uncle' becomes 'Sam' (Uncle Sam is a nickname for the USA).
'raised' becomes 'up' (similar in meaning).
'backward' shows that the letters should be reversed in order.
'sam'+'up'='samup'
'samup' reversed gives 'PUMAS'.
(Other definitions for pumas that I've seen before include "North American mountain lions" , "Big cats" , "American wild cats" , "Large American felines" , "Big felines" .)