animals destined to a cruel death
How would the pilot know this? If he did he'd be morally obliged to report the end user for cruelty to animals, which carries heavy penalties.
But as you said it was in Western Europe you must know that it is illegal to put animals to a cruel death so the situation is just not going to arise, is it?
Even so, no-one can stop you
asking your employer to relieve you of any duty you don't want to do. But do it more than once - or - for the reasons you appear to have chosen, even less than that, and your boss is going to think (quite understandably) that he has a nutter on his hands, and you'll soon find yourself with more time off than you'd planned for.
What's next? Veggie pilots refusing duty because there's meat in the co-pilot's dinner?
ps. What's an "orango"?