In a study published last year, Weary and his colleagues showed calves demonstrate this negative judgment bias after going through the procedure of hot-iron dehorning. Nearly all farms that keep Holstein cattle dehorn them at a young age to protect workers and other cattle. To reduce the pain as much as possible, the cows can be given a sedative to relax them and then a local anesthetic injection to block the immediate pain during the procedure. However, calves do experience some pain as the drugs wear off because of the inflammatory response to the operation.
"We now know that calves in this period of post-operative pain show this depressive-like response," Weary says. "They show this cognitive bias, a pessimistic response to ambiguous stimuli."
Weary and his colleagues saw the cognitive bias after physical pain and wondered if they could use the same judgment bias task as a way of asking the animals how they perceive other things that typically happen to them on dairy farms, such as the early separation from their mothers.
Pessimistic Calves
The researchers compared the responses of calves to ambiguous stimuli before and after separation from their mothers at 42 days of age.
The calves were trained on what's known as a "go/no-go" task. The researchers presented them with either red or white panels on LCD screens and gave them a reward when they approached the white screen, but a time-out if they approached the red screen.
Then they used Photoshop to blend the colors together, creating ambiguous stimuli that were in-between the two colors: a reddish-pink (75% red), a true pink (50% red), and a pale pink (25% red).
Weary and his colleagues found calves were less likely to approach ambiguous screens after both dehorning and separation from their mothers, indicating they were experiencing a negative emotional state after both events. The calves continued to show this negative judgment bias for at least two and a half days after separation.
Although the magnitude of the negative bias was similar following dehorning and separation, it's not clear if magnitude can be used as a measure of the strength of an emotional response.
Caring for Cows
Weary says for him, it all comes back to the welfare of the animals.
"We can't say that separation is just some instantaneous event that may be painful but doesn't bother the animal," he says. "It does bother the animal. It bothers them enough that their mood state changes for at least a couple days."
Weary thinks people are becoming more aware of the complexity of the emotional lives of animals, partly due to the development of scientific methods and tools that can assess that.
Galia ^, via Wikimedia Commons.
In another study earlier this year, Weary and his colleagues showed calves housed in isolation performed worse on cognitive tests than calves reared in groups. Housing calves individually, which is typical on most dairy farms, actually resulted in anxiety and cognitive deficits.
A 2004 study by Cambridge University researchers revealed cows have "eureka" moments, taking pleasure in their own learning achievements. When the cows made improvements in learning, they showed emotional and behavioral reactions that indicated excitement.
"It's interesting to us to come to understand how complex these animals are," says Weary. "It's important to provide a good quality of life for them at an early age, not just in terms of their immediate ability to enjoy life, but also in terms of the long-term effects that we have on these animals."
Reference:
Daros, R. R., Cost, J. H. C., von Keyserlingk, M. A. G., Hötzel, M. J., and Weary, D. M. (2014). Separation from the Dam Causes Negative Judgement Bias in Dairy Calves. PLoS ONE 9(5): e98429. doi: 10.1371/journal.pone.0098429.
