Pain in humans is known to affect mood, making us more likely to interpret ambiguous stimuli as being negative. When shown a half-full glass of water a person in pain is more likely to describe this as “mostly empty”.
The Animal Welfare Program recently published a study that provides the first ever use of this phenomenon of ‘cognitive bias’ to test the effect of common management procedures that cause pain in farm animals.
Dairy producers dehorn calves to reduce the risk of injury to farmers and other animals. Heather Neave, the M.Sc. student responsible for this project, tested dairy calves before and after hot-iron dehorning. Pain control drugs were used, but burn wounds also cause pain hours after the injury and this post-operative pain is not typically treated on farm.
Neave trained calves to either approach or not approach a video monitor depending on the colour of the screen. Using milk as a reward, calves were trained to approach the monitor when it was red and avoid it when it was white. Once trained, calves were tested to see how they responded to intermediate shades of pink.
Before dehorning calves responded to these intermediates as expected; they approached more often when the shade of pink was closer to red. But after dehorning calves showed a pessimistic bias, responding less frequently to these ambiguous screens.
This pessimistic bias is similar to the bias shown by human patients experiencing anxiety or depression, suggesting that the calves were experiencing a low mood state associated with the post-operative pain.
These results provide the first evidence of a cognitive bias associated with pain in non-human animals. These results provide a scientific basis for the recommendation to dairy producers to either avoid dehorning or use post-operative pain control after dehorning.
The study was conducted at the UBC Dairy Education and Research Centre in Agassiz, B.C. Co-authors included graduate students Heather Neave, Ruã Daros and João Costa and Professors Nina von Keyserlingk and Dan Weary.