Neither of any of the above. All of these animals are used and killed for research all the time. The issue for many of them is the personal connection and memo

Neither of any of the above. All of these animals are used and killed for research all the time. The issue for many of them is the personal connection and memories individuals have developed with one species or the other. Then it does matter more if it is a pig or a dog that you are doing harm to. For that matter I have known researchers who are excessively fond of pigs, chicken or cows ...