Animal advocates, scientists, and policymakers often need to understand how their actions impact animal welfare. Making a decision with the greatest overall welfare impact can be challenging when the affected animals come from the same species (e.g., comparing two different cows), but it’s even more difficult when we have to compare different species members (e.g., comparing a cow to a fish).

As humans, we can only approach things with our human perspective. How can we decide whether one action is benefiting animals more than an alternative option?

There are methods to estimate and compare animal welfare, both within and across different species. To do this, researchers usually rely on animal behaviors (e.g., speech patterns) or body functions (e.g., heart rate) and find a way to convert these measurements to an animal welfare estimate. In this paper, the author details the existing animal welfare comparison methods, potential justifications for choosing one method over another, and how to improve our ability to make welfare comparisons in the future. 

The author describes welfare as the overall “goodness” of an individual’s conscious feelings. We therefore need methods to convert behavioral data, which we can measure, to estimates of welfare, which we cannot. However, this can be difficult in practice because two different animals may display two different types of behavior either because their welfare is different or because they’re unique individuals who just happen to behave differently in the same situation.  

To get around this, the author says we have to make a “similarity assumption.” In other words, researchers typically assume that when it comes to two animals, either their range of potential welfare levels (hereout their “capacity”) or their behaviors (hereout their “responses”) are similar.

• Similarity In Capacity: This assumes that both animals’ ability to experience welfare (including their maximum and minimum welfare levels and the strength of their feelings) is roughly the same. In this way, two individuals may display different levels or types of expression — say, one animal may be quieter than the other — but researchers assume they can still experience the same welfare benefits or implications.
• Similarity In Response: In contrast, assuming that two animals will respond to a situation in similar ways means that behaviors are taken as a direct measure of welfare. For example, when one animal is twice as loud as another, researchers may assume their welfare impacts are twice as strong as the other animal’s. This only works if we know for sure that two animals’ behaviors are the same, and that they coincide directly to their welfare experiences. 

Researchers use brain anatomy, evolutionary histories, and other factors to justify using these types of assumptions. In practice, however, the author points out that justifying and applying these assumptions is often unclear due to gaps in our knowledge. This is especially the case when trying to compare across species.

If neither similarity can be justified, the author says we must turn to other metrics. Examples include whether animals are in good health or whether their individual preferences are satisfied. The author believes that no alternative is ideal — they either have debatable links to welfare, or, as in the similarity assumptions, are difficult to use in practice. 

According to the author, more research is needed to improve our understanding of welfare experiences and how to compare them (especially for dissimilar animals and species). Choosing a method is highly context-specific, and none of the methods described above may be justifiable in practice without additional research. Until then, the author recommends that anyone who needs to make a welfare comparison should make it clear why they’re comparing animals, go through every available method, and choose the most reasonable one for the situation at hand while recognizing its drawbacks.   

Animal advocates can help to ensure transparency in the decision-making process by demanding details about how important animal welfare decisions have been made (e.g., by businesses, governments, and other advocates). As our understanding of animal welfare deepens, advocates can eventually work to deter people from using outdated methods of measuring animal welfare.