Wool-growers had clipped back pack and packed it in, sadly (7)
I believe the answer is:
alpacas
'clipped back pack and packed it in sadly' is the definition.
I can't judge whether this definition defines the answer.
'wool-growers' is the wordplay.
'wool' becomes 'alpaca' (alpaca is a kind of wool).
'growers' becomes 's' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'alpaca'+'s'='ALPACAS'
'had' acts as a link.
Can you help me to learn more?
(Other definitions for alpacas that I've seen before include "Sources of wool" , "Llamas with long silky fleece" .)