The measurement of animal welfare is notoriously complex and inherently constrained by the difficulty of assessing the subjective experiences of nonverbal subjects. Yet, to effectively improve animals’  lives, we must clearly understand the relative impact of different living conditions and risk factors on welfare. But how can we compare aversive conditions of a different nature? For example, what is more unpleasant for a pig or chicken: the acute pain from a fracture or prolonged hunger? What about conditions that do not involve tissue damage or unmet physiological needs, such as behavioral deprivations?

To answer these questions, we developed a framework to describe and quantify negative affective states (operationally defined simply as ‘pain’) in animals. It focuses on the two most relevant dimensions of negative affective experiences: intensity and duration. The metric enables estimating the time individuals spend in negative affective states of a physical or psychological nature of different intensities as the result of one or more harms (e.g., diseases, injuries, deprivations). A new notation protocol (the Pain-Track) is used in which the duration of the experience is represented along the horizontal axis and intensity is represented by four categories in the vertical axis. Pain experiences are partitioned into temporal segments, where hypotheses for the experienced duration and intensity are proposed based on existing welfare indicators (e.g., neurophysiological, behavioral, anatomical, evolutionary). The analytical framework can be similarly applied to quantify positive affective experiences.

This structure forces transparency about assumptions and uncertainties, highlights knowledge gaps, and enables estimates to be continuously adjusted. Because the Cumulative Pain metric is based on parameters with a broadly common biological meaning, it provides the much needed interoperability among assessments of animal welfare in different species. It enables comparing the impact of practices and living conditions, policies and interventions, and the calculation of welfare footprints of animal-sourced products using a universal measurement unit: time in pain of different intensities. The results of applying this method have now been used to inform decision-making by institutions and organizations working with farm animal welfare.