Destroyed. I hate that wimpy word as in "the animal was destroyed". It's like saying in journalism that someone "passed away" or "went to his reward". A person "died", suffered "death" or was "killed". Write plainly and use straightforward terms. When an animal is put to death it is simply "killed" or "killed by lethal injection by the vet" or "shot dead by the police officer". What on earth does "destroyed" mean? Destroyed the animal's reputation? Blown-up with dynamite? Don't wimp it with polite terms for unpleasant facts.
This is about a bigger duty than one word. A reporter's job is to tell the truth plainly, even when the truth is uncomfortable. The soft word, the polite word, the word that lets everyone look away, is nearly always the wrong word, because it blurs exactly the thing the reader needs to see clearly.
The trade is full of these dodges. People do not "pass away", they die. A patient is not "lost", they die. Soldiers are not "neutralised", they are killed. A company does not "let staff go", it sacks them. A government does not "misspeak", it lies. Each soft phrase is a small act of cowardice, and readers can smell cowardice in writing a mile off.
Now, there is a difference between plain and brutal, and you must judge it with care. Writing plainly does not mean writing cruelly. When you report a death you can be straight and still be kind, choosing the plain word "died" while treating the family with respect. Plain language and decency are not enemies. The enemy is the foggy phrase that hides what happened.
So say died. Say killed. Say sacked. Give the reader the hard, clear word, and trust them to handle the truth. That trust is the whole basis of the job.