Animal in its second year (8)
I believe the answer is:
yearling
'animal in its second year' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for yearling that I've seen before include "Animal between 1 and 2 in age" , "Relaying (anag.)" , "Young racehorse" , "A racehorse under 2" , "Racehorse that is 12 months old" .)