Lots of certain animals in containers (5)
I believe the answer is:
packs
This clue could be a double definition.
'lots of certain animals' is the first definition.
'packs' can be an answer for 'lots' (pack is a kind of lot). I am not certain of the 'of certain animals' bit.
'containers' is the second definition.
(pack is a kind of container)
'in' is the link.
Can you help me to learn more?
(Other definitions for packs that I've seen before include "Cartons" , "prepares to leave" , "Given cards" , "Groups of hunting animals" , "Sets of playing cards" .)