Animals record released 50 years ago (6)
I believe the answer is:
horses
'animals' is the definition.
(I have seen 'Domesticated animals' mean 'horses' so perhaps 'animals' could also mean 'horses')
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for horses that I've seen before include "See 1" , "Hoofed mammals (which go with 19 4)" , "Equine beasts" , "Domesticated animals" , "Equine animals" .)