For those who continue to doubt the studiability of distress or suffering or misery in all of its forms in animals, consider the following thought experiment: If the government were to come up with a billion dollars in research funding for animal distress, would that money go a-begging? We can study these states just as we studied pain—excellent work on boredom by Franciose Wemelsfelder in a volume on laboratory animal welfare I co-edited made the methodology for such study quite explicit. (Wemelsfelder, 1990) And when the ideological scales fall from our eyes, we realize that the work of scientists like John Mason (Mason, 1971), Seymour Levine (Levine, 1990) and even the odious work of Harlow do provide clear ingression into animal unhappiness. Even more promising, it has recently become legitimate to talk of animal happiness, a notion I have argued elsewhere is in fact clearer than that of human happiness (Rollin, 2004).
Rollin, Bernard E., "Recognition of Distress in Animals – A Philosophical Prolegomenon" (2009). Animal Sentience, Intelligence, and Behavior. Paper 12.