It is worth noting that human life too has no moral value, only the feelings of pleasure and suffering do. There are three problems with taking a human life: (a) at the moment of the killing itself he suffers; (b) the loss of his future pleasures; (c) suffering to those around him who have lost him, and the loss of the pleasures he would have produced for others. Problem (a) is not difficult, because when his day comes he will suffer the pain of death anyway, so one only needs to ensure that in killing him now he suffers no more. Problem (b) can be debated at great length (parallel to the discussion of “wrongful life”), and in my opinion it has no substance. Problem (c) is solved if you kill those around him as well (and overall perhaps all of humanity). And that brings us to the conclusion that morally speaking there is no problem at all with wiping out all of humanity in an instant. And from that, apply the same to animals.
As for the act of killing itself, of course it has no importance whatsoever (as any sensible person who can tell his flour from his wheat understands: there is no moral importance to any act in itself. The command is not to perform actions that bring about bad states of affairs, and nothing more).