The Benefits of Increasing Livestock Species in Comparative Cognition Research
Abstract
The future of comparative cognition should incorporate more studies that use livestock species (i.e., cattle, sheep, goat, swine and chicken models). Livestock can be considered a dual-purpose model, with the potential to increase the efficiency of comparative biomedical, psychological, and agricultural research. This increase would also enhance efforts in animal welfare science by targeting more precise and objective methods to evaluate affective states of animals using cognitive methods.
Keywords: animal welfare, cognition, farm, livestock
A memorable advertising campaign for the California dairy industry, created by Deutsch Inc. Advertising, stated that “great cheese comes from happy cows, and happy cows come from California” (Stampler, 2012). This catchphrase is a great example of how the field of comparative cognition (specifically, understanding the affective state of nonhuman animals) is expanding to address ethical concerns of animal use, especially the welfare of domestic livestock. Although there are scientific societies dedicated to the study of animal welfare (e.g., International Society of Applied Ethology), for decades the research has focused on overt indicators of poor welfare such as illness, injury, or performance of abnormal behaviors. With the advances made in the study of animal sentience, which is the capacity of an animal to have subjective experiences whether conscious or unconscious with positive or negative valence (Browning & Birch, 2022), the future of comparative cognition may play an essential role for veterinary medicine, animal welfare science, and animal agriculture.
Animal Welfare Applications
The validation of pain or pleasure indicators in animals using comparative cognition is an area of research that will be highly valued by livestock producers, small- and large-animal veterinarians, veterinary pharmaceutical companies, and pet owners. Many animal welfare studies use behavioral measurements of conditioned responses to infer subjective pain or pleasure experience, such as conditioned place or reward preference (Fraser & Duncan, 1998). For example, injured rats and lame chickens will work to consume more water that contains a pain-relieving drug over pure water as compared with noninjured conspecifics (Danbury et al., 2000; Persinger, 2003). How an animal processes, stores, and acts on environmental information can give us clues as to whether it is in a more positively or more negatively valenced affective state.
Recent research attempting to investigate the affective state of animals after an intervention or treatment often implements a modified cognitive bias test. Evidence from the human and animal literature suggests that pessimistic judgments of ambiguous stimuli are indicators of negative affective states, such as anxiety or depression (Hallion & Ruscio, 2011; Mendl et al., 2009). This appraisal of stimuli can be the result of conscious mental checks (e.g., dangerous? familiar?) and memory recall, or the result of rapid and automatic reactions to stimuli (Grandjean & Scherer, 2008; Mendl et al., 2009). Using operant conditioning, animals learn to distinguish stimuli that vary on one dimension (e.g., size, color concentration, location) and associate a particular stimulus with a pleasant outcome (e.g., food reward) and another stimulus with an aversive outcome (e.g., shock, time-out). The animals’ response to an ambiguous, or intermediary, stimulus indicates whether they are expecting the pleasant outcome (i.e., optimistic) or the aversive outcome (i.e., pessimistic). Although this approach requires ample training time and is vulnerable to disengagement by the animals after multiple nonrewarded trials, it provides animal welfare scientists with a proof-of-concept tool to provide answers to questions such as “Is this stocking density for piglet impacting the animals’ affective state?” (Scollo et al., 2014) or “Are the dairy calves still in pain from the hot-iron removal of horn buds?” (Neave et al., 2013).
Dual-Purpose Psychological Research
The United States has approximately 66,000 pork producers, which market an average of 140 million hogs each year (Cook & Schultz, 2022). Although these animals are produced for the primary purpose of slaughter and human consumption, there is a significant opportunity to take advantage of this expansive animal population to conduct mutually beneficial cognitive research. A few examples of early cognitive research used livestock species, such as Walk and Gibson’s (1961) research on depth perception in chickens; however, very few examples of comparative cognition research used common livestock species (e.g., cattle, goat, sheep, swine). There have been academic workshops (e.g., Michigan State 2004), government funding (e.g., USDA and NIH Dual Purpose with Dual Benefit program), and scientific commentaries (Ireland et al., 2008) on the advantages of using livestock as dual-purpose models for biomedical research. And although the use of sheep and swine in translational medicine has increased (e.g., transgenetic animals; Prather et al., 2003), there is very little research on the practicality of using livestock for animal models in psychological or cognitive research.
Given that the overall prevalence for stress-induced anxiety disorders is significantly higher for women than men (Pigott, 2003), the mechanisms underlying these sex differences need to be further investigated. This need is especially pertinent given that available therapeutics to treat anxiety disorders have not proven to be completely effective, even in combination with cognitive-behavioral therapy (Davidson et al., 2004; Otto et al., 2000). A common method to induce anxiety via social conflict in animals is through the Social Defeat Test. In this test, a focal animal is placed in an unfamiliar arena as an “intruder” and is the recipient of repeated aggression from a “resident” animal (Solomon, 2017). A major drawback to using the rodent model for Social Defeat testing is that, for most species, females do not engage in contexts of social stress or aggression, and therefore males are disproportionately overrepresented (Beery & Zucker, 2011; Haller et al., 1999). For future research on the mechanisms of anxiety disorders to have a higher relevance for human health, the mechanisms need to be replicated in a model with more translational value.
Female pigs form complex social relationships, they maintain a flexible dominance hierarchy through indirect or direct aggression, and the anatomy and development of the pig brain closely resembles that of the human brain (D’Eath & Turner, 2009; Lind et al., 2007). Using a comparative cognition approach, researchers may find that female pigs may serve as an ideal animal model of anxiety. Several studies that assessed both physiological and behavioral outcomes found that, as in humans (Chorpita & Barlow, 1998), mild and extreme social stress can cause sustained anxiety in pigs (Andersen et al., 2000; Goumon & Špinka, 2016; Janczak et al., 2003). Furthermore, peer interactions and social status during adolescence are key to the development of chronic anxiety in humans (La Greca & Lopez, 1998) and pigs (Ruis et al., 2001).
The domestic pig is a preferred preclinical model in several areas, including cardiovascular, nutrition, and infectious diseases, because it is anatomically and physiologically similar to humans (Miller & Ullrey, 1987). There is a need to understand if we are missing an incredible opportunity to observe these animals while they are alive, as it could provide vital information about social cognition, learning, and emotional development. With an open mind and a goal to practice sustainable research, researchers could have more opportunities in the future to advance the comparative cognition field into the applied animal welfare sector of veterinary medicine.
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