I have a very old dog, he doesn’t walk any better, he’s blind, he suffers a lot, often bites who passes by because he thinks he’s another animal, in these cases what should I do? Does halakha in this case allow to sacrifice the dog so he doesn’t suffer anymore?
You don’t have to sacrifice the dog, but you are allowed to kill it or give it to be killed, to end its suffering, because it is harming other animals, and because at this point keeping it alive is an unnecessary expense. Needless to say, it should be killed in a way that will cause it the least suffering.
Nefesh Kol Chai chap. 5-3,5,6,7, ftnt. 16 in the name of R’ Eliyasiv zt”l that it should be killed in a way that minimizes its pain.