Pain affects calves’ emotional state: study

Pessimistic attitude | Researcher says the test linking calf pain to depression may apply to other animals and situations

LINDELL BEACH, B.C. — It may be relatively easy to measure pain in animals by observing behavioural or physiological changes, but understanding their emotional state is more difficult.

Researchers at the University of British Columbia have conducted the first ever judgment bias test on a non-human species. They found that calves that recently had their horns removed showed signs of pessimism, or negative interpretations.

“My interest in pain started when I was working at the UBC Dairy Education and Research Centre and helping with research projects,” said Heather Neave, a recent master’s graduate at UBC’s animal welfare program who led the project.

“One of my chores at the farm was helping to dehorn the calves, and I noticed that calves often appeared despondent in the hours after the procedure. Farmers often give their calves a local (lidocaine) block. This helps to control the immediate pain but not the pain the calves experience in the hours after hot-iron dehorning.”

It is becoming more common for farmers to treat the local pain, but it’s often overlooked for the time period after dehorning, she said. It was the hours following the dehorning procedure that she was most interested in.

“The available research shows that not only is there an immediate pain response but it continues for at least 24 hours.”

Human studies have shown that an individual’s emotions can influence how they process information, including their attention, memory and judgment. These phenomena are known under the umbrella term cognitive biases.

In judgment biases, people suffering depression may judge an ambiguous test negatively. For instance, in describing a partially filled glass of water, they will describe it as half empty rather than half full.

Neave’s study, published in the December issue of the science journal PLoS One, defined pain as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage.”

It used 17 male Holstein calves, starting at around three days of age. They were housed in individual sawdust bedded pens and managed according to standard farming protocols.

A separate pen was used for the test. Equipment included a nose touch start button, a 48 centimetre computer monitor that would display either a red (positive) screen or a white (negative) screen, and a milk bottle dispenser that would, or would not, dispense a reward.

Each screen colour was displayed for three seconds. Calves learned that they needed to approach and touch the screen to receive a milk reward from the bottle if it was red but stay away from the screen if it was white because milk would be withheld.

The colour red was chosen for its ease of recognition by the calves.

Neave spent three weeks clicker training the calves to nose touch the start button, interpret the screen colour and decide whether to approach and touch the screen.

The calves were trained and tested at the same time twice a day, and training and testing sessions lasted 15 minutes for each animal. The same number of displays of positive or negative colours was displayed during the duration of the test.

Once the calves were trained, they were tested with three shades of pink: dark, medium and light.

The pink shades offered an ambiguous challenge for each calf because they are a mix of red and white.

Before dehorning treatments they interpreted the near-positive and near-negative pink screens the same way they did with the original red or white training screens. They treated the midway pink colour as intermediate, as expected.

However, after dehorning, the calves approached the ambiguous pink screens much less frequently.

“They interpreted these pink screens negatively,” said Neave.

“This pessimistic bias indicated that the calves believed they were less likely to receive a milk reward and is indicative of a negative emotional state similar to depression or anxiety.”

Neave’s study is consistent with earlier research that found post-operative pain can persist for 24 hours.

The calves exhibited the pain by head shaking, head rubbing and ear flicking. As well, they experienced an elevated heart rate and cortisol levels for several hours.

The calves were tested at six hours following dehorning, which is the peak of pain-associated behaviour, and at 22 hours, which is when pain behaviour begins to decline. The calves’ judgment bias of the ambiguous screen remained pessimistic in both tests.

The calves were about 30 days old.

“When starting the experiment, I wasn’t sure exactly how the training of the calves would go for the experiment, but I was amazed at how quickly they were able to learn it,” she said.

“The intelligence of the calves is something that really interests dairy producers and others who I have told about my study, especially when I show them the video of the calves performing the task.”

Neave hopes the research will encourage farmers to consider the emotional impact of dehorning and move toward treating the pain associated with this procedure.

“Xylazine and lidocaine can be used to treat local pain at the time of dehorning,” she said. “Ketoprofen and meloxicam are highly encouraged for treating post-operative pain for the 24 hour period following dehorning. The bias is an indication that something is going on cognitively, and it’s not simply a sensory response. This type of experiment could be used to investigate the effects of other common procedures, like castrating or tail–docking, on emotion and cognition.”

The 2013 edition of the Code of Practice for the Care and Handling of Beef Cattle requires dehorning to be done as early as possible with veterinary advice on pain control.

The recommendations are to avoid dehorning at the time of weaning to minimize stress and to consider a breeding program using homozygous polled bulls to eliminate the need for disbudding or dehorning.

“Farmers’ practices are definitely changing,” said Neave.

“In my experience, dairy producers realize that these practices cause pain and welcome changes in practices that can prevent or reduce the pain that calves experience.”

UBC researchers are also using cognitive bias tests to look at the emotional impact of calves when separated from their mothers.

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