Machado, M., Freitas Silveira, R. M., Machado Bittar, C. M. et al. 2023. Can the emotional state of calves be noticed by their facial expression and heart rate? Applied Animal Behaviour Science 260, 105874.

The aim of this study was to identify whether or not dairy calves change their facial expression and heart rate according to their emotional state when subjected to a stroking or umbrella stimulus. Thirty-two mixed-breed Holstein calves of different ages were submitted to stroking and umbrella stimulus. For the stroking stimulation, a researcher performed stroking for 1 min in the neck region with continuous and frequent movements (about 40–60 movements per minute) to simulate the speed with which an animal would receive allogrooming. As for umbrella stimulus, a researcher positioned himself one meter in front of the calf, with an umbrella in his hand, without making eye contact. Then, the umbrella was suddenly opened and remained open for one minute. The eyebrow position, mouth, eye white area, nostril area and heart rate were investigated. For the continuous variables, eye white area, nostril area and heart rate we used the linear mixed effects. For the binary variables, mouth (open or closed) and eyebrow (raised or normal). We used the generalized linear mixed model with logit link function. The variables eye white area, nostril area, mouth and eyebrow did not present significant effects (P > 0.05) as a result of the stimulus. However, the heart rate showed a significant difference (F(1150) = 15.264, P < 0.001) according to the stimulus the animals received. Dairy calves do not express facial changes in their emotional state when subjected to stroking or umbrella stimuli, but there is a reduction in heart rate relates to the valence of a stimulus.

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