The Half-Empty Glass: Dairy Calves And Pessimism

In humans, pessimism and optimism are related to personality traits like neuroticism and extroversion. In the case of non-human animals, studies have shown that rats can be pessimistic, and those individuals are more likely to develop depressive states; that pessimistic dolphins showed fewer affiliative behaviors; and that pigs have judgement bias responses, and those individuals with reactive personalities were affected by their environment and showed pessimistic responses.

So far, scientists have established that emotional states affect attention, memory, and judgement biases in different species. Various studies have used tests to assess “ambiguity responses” to a specific task. Depending on the direction of the response (e.g., positive = reward, negative = no reward), scientists have been able to assess the emotional state of animals. These studies have mainly focused on animal welfare; for example, animals exposed to negative experiences (e.g., painful procedures) were more pessimistic, and animals exposed to positive experiences (e.g., environmental enrichment) were more optimistic.

This study investigated the relationship between pessimism and personality traits in dairy calves. Personality traits were identified in 32 dairy calves using four tests that assess the calves’ social motivation and fearfulness. The personality and judgment bias tests were performed when calves were 25 and 50 days of age. Social motivation was measured by the time a calf took to reach the herd, and fearfulness was measured by the time a calf took to touch a novel object and an unfamiliar human.

Judgement biases were assessed by placing a calf in a small room where they first learned the location of a bottle with milk (reward) and an empty bottle plus an air blower (“unrewarded event”). The bottles were located on opposite sides of the room. Once calves learned the positive and negative locations, ambiguous responses (empty bottles) were added: one was placed closer to the rewarded corner, another closer to the unrewarded corner, and one was placed in the middle (between the rewarded and unrewarded locations). The time a calf took to approach an ambiguous location was used to measure her judgement bias. So, the longer it took to approach an ambiguous location, the more pessimistic an individual was.

In the personality tests, calves were consistent in the degree of fearfulness or sociability they showed during the two testing sessions. In the judgment bias tests, the researchers found that calves took longer to reach a location that was farther from the rewarded corner, and the time decreased depending on the distance to the rewarded corner. Finally, the study found that the fearfulness trait was related to the time a calf took to approach the ambiguous location, meaning that more fearful calves were also more pessimistic. Judgement bias results were not associated with calves’ social motivation.

The study’s authors describe how these results could affect how we see animal welfare: based on their personalities, animals that are pessimistic may not reach or enjoy opportunities to improve their welfare. For example, pessimistic animals could potentially miss out on environmental enrichment due to fear of new objects. On the other hand, optimistic animals may suffer more when their environment does not satisfy their expectations, leading to frustration, boredom, and worse.

For animal advocates, this study — though it does use captive animals to draw its data — increases our knowledge of the personality dimensions of calves. It also makes us consider that the inconsistency observed in previous cognitive bias may have been influenced by individual differences in animal personalities such as optimism and pessimism. Overall, studies like this could help us craft animal welfare measures that are more effective for more fearful animals. Simultaneously, it shows just how important it is to recognize that non-human animals, like humans, have individual personalities that affect how they experience the world.