How do we set thresholds for animal welfare?

Recommendations for animal welfare often rely on reference to different welfare thresholds. While some welfare science simply aims at the comparative goal of welfare improvements (i.e. increasing the level of welfare from its previous baseline), other applications aim at the more absolute goals of achieving good welfare, or creation of a life worth living. The latter cases involve a normative element in judging where the relevant thresholds lie. Here I discuss some of the commonly used thresholds and outline some principled ways of setting their levels.