Prevalence of the protein SIgA may reflect an animal’s psychological and physiological well-being better than other non-invasive methods.

One of the biggest issues animal advocates encounter is proving that animals objectively suffer. Part of the problem with making that statement, from a scientific standpoint, is that the process of evaluating animals’ psychological or physiological well-being can cause further stress or harm, thereby altering the results.



Researchers have tried to counteract this unintended, potentially negative effect by looking for non-invasive, accurate physiological biomarkers that provide a picture of an animal’s subjective experience. Unfortunately, prior methods, such as measurements of activity of the hypothalamic-pituitary-adrenal axis (as expressed by the prevalence of glucocorticoids) have been unpredictable. Even though glucocorticoids can signal a physiological response to stimuli, they do not express valence; in other words, while we know that something is measurably changing, we’re not sure whether it’s a positive or negative response.



Nonetheless, other biomarkers may enable more accurate assessments. In this research review, scientists focus on the potential of the antibody isotope Immunoglobulin A (IgA) –specifically, the secretory form (SIgA) – as a non-invasive indicator of the stress-immune system response.



IgA is a promising biomarker because it’s a protein whose synthesis is influenced by stress-immune interactions, and scientists believe that it is indicative of an individual’s overall immune health. To summarize briefly, there is evidence that the immune system is weakened by stress, so the reasoning is that lower levels of SIgA mean more stress and, therefore, reduced overall well-being and health.



Measuring animals’ subjective welfare using SIgA has two main benefits compared to other methods: first, SIgA can be collected through saliva or fecal samples, so collecting it would not disturb the animal or distort the objective results; second, it seems to be the only biomarker whose prevalence expresses a correlation with stress and immune health.



However, the authors caution that SIgA may sometimes cause confusing results because its amount may initially increase in response to both positive and negative stimuli; nonetheless, long-term results will typically only reflect a response to negative stimuli. Thus, it’s usually necessary to measure SIgA over a sustained period of time. The researchers advise others to collect a baseline measurement before initiating a study of responses, and taking frequent samples throughout the study to get the most accurate results. They also note that different species may have different responses, and that it may be useful to measure other biomarkers in conjunction with SIgA to account for any discrepancies.



Overall, SIgA seems to be an effective and universal means to understand an animal’s personal experience. By incorporating SIgA measurements into the standard model of thinking about and analyzing animal welfare, the authors are hopeful that animal care specialists and animal industries will incorporate the practices into their work, and thereby improve animals’ welfare overall.

