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Affect-driven cognitive biases can be used as an indicator of affective (emotional) state. Since humans in negative affective states demonstrate greater responses to negatively-valenced stimuli, we investigated putative affect-related bias in mice by monitoring their response to unexpected, task-irrelevant stimuli of different valence. Thirty-one C57BL/6J and 31 DBA/2J females were individually trained to return to their home-cage in a runway. Mice then underwent an affective manipulation acutely inducing a negative (NegAff) or a comparatively less negative (CompLessNeg) affective state before immediately being tested in the runway with either an ‘attractive’ (familiar food) or ‘threatening’ (flashing light) stimulus. Mice were subsequently trained and tested again (same affective manipulation) with the alternative stimulus. As predicted, mice were slower to approach the light and spent more time with the food. DBA/2J mice were slower than C57BL/6J overall. Contrary to predictions, NegAff mice tended to approach both stimuli more readily than CompLessNeg mice, especially the light, and even more so for DBA/2Js. Although the stimuli successfully differentiated the response of mice to unexpected, task-irrelevant stimuli, further refinement may be required to disentangle the effects of affect manipulation and arousal on the response to valenced stimuli. The results also highlight the significant importance of considering strain differences when developing cognitive tasks.

The number of animals bred, raised, and slaughtered each year is on the rise, resulting in increasing impacts to welfare. Farmed animals are also becoming more diverse, ranging from pigs to bees. The diversity and number of species farmed invites questions about how best to allocate currently limited resources towards safeguarding and improving welfare. This is of the utmost concern to animal welfare funders and effective altruism advocates, who are responsible for targeting the areas most likely to cause harm. For example, is tail docking worse for pigs than beak trimming is for chickens in terms of their pain, suffering, and general experience? Or are the welfare impacts equal? Answering these questions requires making an interspecies welfare comparison; a judgment about how good or bad different species fare relative to one another. Here, we outline and discuss an empirically-based methodology that aims to improve our ability to make interspecies welfare comparisons by investigating welfare range, which refers to how good or bad animals can fare. We begin our proposal with a theory of welfare. We operationalize that theory of welfare by identifying metrics that are defensible proxies for measuring welfare, including cognitive, affective, behavioral, and neuro-biological measures. We assign differential weights to those proxies that reflect their evidential value for the determinants of welfare, such as the “Delphi'' structured deliberation method with a panel of experts. Then we review the evidence and score its quality to ascertain whether a particular taxa may possess the proxies in question to construct a taxa-level welfare range profile. Finally, we use a Monte Carlo simulation to generate an overall estimate of comparative welfare range relative to our hypothetical index species - humans. Interspecies welfare comparisons will help facilitate empirically informed decision-making to streamline the allocation of resources and to ultimately better prioritize and improve animal welfare.

Billions of animals across many taxa are extensively farmed, with critical impacts on animal welfare. Societal efforts to reduce animal suffering lack rigorous and systematic approaches that facilitate maximising welfare improvements, such as informed funding allocation decisions. We present a multi-measure, cross-taxa framework for modelling differences in pain, suffering, and related cognition to assess whether certain animals have larger welfare ranges (how well or badly animals can fare). Measures include behavioural flexibility, cognitive sophistication, and general learning. We evaluated 90 empirically detectable proxies for cognition and welfare range (henceforth 'proxies') in pigs, chickens, carp, salmon, octopus, shrimp, crabs, crayfish, bees, and silkworms. We grouped a subset of proxies into: A) 10 ideal proxies and B) 10 less ideal proxies but with sufficient data for interspecies comparisons. We graded the strength of evidence per proxy across taxa, and constructed a cognition and welfare range profile, with overall judgement scores (ranging from likely no/low confidence to yes/very high confidence). We discuss the implications of comparisons and highlight key avenues for future research. This work is timely, given recent indications of significant political will towards reducing animal suffering, such as the inclusion of cephalopods and decapods in the Animal Welfare (Sentience) Bill following a UK government-commissioned research review. Given the novelty and robustness of our review, we believe it sets a new standard for investigating interspecies comparisons of cognition and welfare ranges and helps inform future research. This should help streamline funding allocations and improve the welfare of millions of farmed animals.