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Does dehorning lead to depression?

Heather Neave Published on 24 February 2014
dehorning a calf

We all know that dehorning is painful. But have you thought about how calves feel after dehorning?

Research on humans has shown that our emotions influence the way we think and interpret information. Depressed individuals are more likely to expect that future events will be negative.

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They are less willing to take risks when having to make decisions regarding everyday life dilemmas. They also tend to interpret ambiguous stimuli more negatively, such as judging a glass to be “half-empty” rather than “half-full.”

Humans experiencing pain show the same pattern – they tend to choose negative pain – related meanings of ambiguous-sounding words (e.g., pain versus pane, or bury versus berry). These negative interpretations of uncertain information are called judgment biases.

If humans in pain and depressed patients show changes in the way they think, is it possible that calves experiencing pain from dehorning also show pessimistic judgment biases? Do calves see the glass as “half-empty” after dehorning?

The challenge is that we cannot just ask the calves how they feel – we needed to create clever experiments to “ask” calves how they judge ambiguous events. A recent study from the University of British Columbia’s Animal Welfare Program set out to do just this.

As the master’s student in charge of the project, I trained calves to approach a computer screen when the color of the screen was red. For this, the calf received a few sips of fresh milk. If calves approached the screen when it was white, they were not given milk and instead were given a “time-out” of one minute with no color on the screen. The calves were quick learners and soon approached the screen only when it was showing red.

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Once the calves were trained, I was able to test their responses to ambiguity. I continued to display the red and white screens as before, but every once in a while I displayed one of three shades of “pink” – one shade was close to red, one close to white, and one was an equal blend or red and white.

I expected that calves would treat the near-red screen like it was red and approach, and would treat the near-white like white and not approach. I also expected that calves would show a mixed response to the 50-50 red-white blend and approach the screen about half the time. This was exactly what the calves did when they were tested before dehorning.

Following standard practice for this and other farms in Canada, all the calves received a local block with lidocaine so that pain during the dehorning was not an issue.

However, other research has shown that calves experience pain for up to 24 hours after the procedure, so calves were tested at two time points: once at six hours, when the local block had worn off and pain is expected to be highest, and once at 22 hours, when pain is thought to ease.

After dehorning, calves continued to approach the red and white screens as previously trained but now approached the pink screens less frequently ( Figure 1 ).

After dehorning, calves continued to approach the red and white screens as previously trained but now approached the pink screens less frequently

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Now that the calves were feeling pain from the dehorning procedure, the calves were more wary of going to the pink shades. Calves responded as if they expected to receive a “time-out” for their response instead of the milk reward. This is what we call a pessimistic bias, much like the depressed human seeing the glass as half-empty.

The researchers concluded that these pessimistic responses indicate a negative emotional state in calves, similar to depression or anxiety in humans, and this bias persists for at least 22 hours after dehorning.

I think these findings are particularly compelling, and this work provides strong evidence that dehorning has an emotional impact for the animals despite providing the calves with lidocaine to treat the immediate pain.

Many farms provide lidocaine as a local block to prevent pain during the dehorning. This drug is effective for about two hours. Unfortunately, the inflammatory pain associated with a burn injury lasts much longer and needs to be treated with anti-inflammatory drugs.

Work with your veterinarian to develop a proper treatment plan. It is this pain, which occurs after the local lidocaine block wears off, that is often not treated on dairy farms.

Our study really highlights the importance of considering the pain that follows the procedure – calves were experiencing negative feelings even 22 hours later. So far farmers are doing a good job of treating immediate pain, but we need to go one step further to address this longer-term pain.

More importantly, our work shows how we can use judgement bias tests to ask calves and cows how they “feel” about the housing and management decisions we make. This provides a new scientific method to better understand and improve cattle welfare. PD

The study is published in the open-access journal PLoS ONE .

PHOTO: If humans in pain and depressed patients show changes in the way they think, is it possible that calves experiencing pain from dehorning also show pessimistic judgement biases? Do calves see the glass as ‘half-empty’ after dehorning? Photo by PD staff.

Heather Neave
  • Heather Neave

  • Master's Student
  • University of British Columbia
  • Email Heather Neave

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