Endless gloom and wet weather brings animal disease (7)
I believe the answer is:
murrain
'animal disease' is the definition.
(murrain is a kind of animal disease)
'endless gloom and wet weather' is the wordplay.
'endless' means to remove the last letter.
'gloom' becomes 'murk' (I've seen this before).
'and' means one lot of letters go next to another.
'wet weather' becomes 'rain' (I've seen this before).
'murk' with its last letter removed is 'mur'.
'mur'+'rain'='MURRAIN'
'brings' acts as a link.
(Other definitions for murrain that I've seen before include "Cattle disease" , "Cattle plague" , "Cattle-plague" .)