Strike-breaker (derogatory) - disease of cattle and sheep (8)
I believe the answer is:
blackleg
(Other definitions for blackleg that I've seen before include "One who breaks a strike by working" , "Scab, strikebreaker" , "Strikebreaker - disease of farm animals" , "one not out, controversially" , "Person who works while others are on strike, having dark limb" .)