This situation probably doesn't apply to people on HN, but as a thought experiment: In a pre-industrial society or one where rule of law has broken down I could see a situation where the labor and protection provided by an animal made them a part of the family in a very real way. In those circumstances I could see that the life of an animal might be much more important than the life of an outsider; even if only in a strictly practical sense.

Note that I'm not necessarily trying to argue whether that would be correct in a moral sense.