Disbudding dairy calves is a common but painful procedure to prevent horn growth. Even when controlling for the immediate, intra-operative pain, post-operative pain can last for days after the procedure. Anhedonia, the reduced ability to experience pleasure, is associated with low mood in humans. In the current study, UBC researchers report the first evidence of anhedonia after disbudding in dairy calves. They found that calves reduced their consumption of a sweet solution for at least 5 days after the procedure. The researchers also found evidence of individual differences in this response. Calves that were rated as more pessimistic before disbudding showed more evidence of anhedonia after disbudding, suggesting that these animals were particularly vulnerable to pain. These results emphasize the importance of preventing post-operative pain, and the importance of individual differences in pain vulnerability.
Read the full study: https://doi.org/10.1371/journal.pone.0242100
The above videos show how researchers assessed pessimism in the calves. Calves were trained to approach a milk bottle for a drink of fresh milk, from a bottle placed on the far right of the pen. When the bottle was placed on the far left of the pen calves did not get the milk reward. After this training phase, calves were tested using ambiguous cues, i.e. with milk bottles placed in locations between the positive and negative training positions. The first video shows the response of a more optimistic calf – this calf quickly approaches the bottle in the test location. In contrast, the second calf shows a more pessimistic response – this calf stays close to the training location on the right side of the pen and never approaches the test bottle.