Heart rate variability, eye temperature, and spontaneous blink rates as measures of emotions in working donkeys

Quantitative measures of emotion play a crucial role in objectively assessing animal welfare. However, there is currently no research available on donkey emotions. Our study investigated spontaneous blink rate (SBR), eye temperature (ET), and heart rate variability (HRV), quantified as RMSSD (root mean square of the successive differences between beat-to-beat intervals), as potential measures of donkey emotions. Thirty-four donkeys were exposed to three treatments: positive, negative, and control. The positive and negative treatments were feeding high-quality lucerne and exposing donkeys to the sound of hair clippers, respectively. The control group was recorded standing in their usual environment, and were not subjected to any additional positive or negative stimuli. Data were analyzed using linear models. SBR increased during positive treatment and decreased with the negative treatment compared to the control. An increase in ET was found for both negative and positive treatment compared to the control. We found a positive relationship between changes in SBR and HRV (estimated = 1.32, t = 5.44, p < 0.001), whereas negative relationships were found between changes in ET and HRV (estimated= -12.76, t= -5.93, p < 0.001). ET, SBR, and HRV may act as indicators of emotions in donkeys. Additional studies should investigate these metrics through a thorough analysis of donkey behavior.