Are you ready for a challenge? Personality traits influence dairy calves' responses to disease, pain, and nutritional challenges

Dairy calves routinely experience disease, pain, and nutritional stressors such as diarrhea, dehorning, and weaning early in life. These stressors lead to changes in behavioral expression that varies in magnitude between individuals, where a greater magnitude change would suggest lower resilience in individuals to a stressor. Thus, this study first aimed to quantify the individual variation in magnitude change in feeding behaviors and activity in response to a bout of diarrhea, dehorning, and weaning. The next objective was to then investigate if personality traits were related to this magnitude of behavioral response in dairy calves, and thus their resilience toward these stressors. Calves were followed with 2 precision livestock technologies (e.g., an automatic feeding system, and leg accelerometer) to track behavioral changes in response during the time when the stressors were present. The automatic feeding system provided daily measures of milk intake, drinking speed, rewarded and unrewarded visits to the milk feeding station, and calf starter intake. The leg accelerometer provided daily measures of steps, activity index, lying time, and lying bouts. At 23 ± 3 d of age, Holstein dairy calves (n = 49) were subjected to a series of standardized personality tests that exposed the calf to novelty and fear stimuli. Factors extracted from a principal component analysis on the behaviors from the personality test were interpreted as personality traits: Factor 1 (fearful), Factor 2 (active) and Factor 3 (explorative). The magnitude changes in behaviors from the precision livestock technologies were calculated relative to the behavior performed on the day the stressor occurred (i.e., day of diagnosis, day of dehorning, day weaned). Linear regression models were used to determine whether calf scores on each factor were associated with magnitude change in behavior for each of the stressor periods with day relative to the stressor included as a repeated measure. Models were run independently for the period leading up to and following each stressor. We found that calves varied in their behavioral responses to diarrhea, dehorning, and weaning stressors, despite being reared in the same environment and experiencing consistent management procedures. Additionally, personality traits measured from standardized tests were associated with both the direction and magnitude of change in behaviors around each stressor. For instance, with diarrhea, calves that were highly fearful had a greater magnitude change in milk intake and drinking speed following diagnosis than the least fearful calves. With dehorning, calves that were highly explorative had a greater magnitude change in lying time when dehorned, but a smaller magnitude change in lying bouts and drinking speed following dehorning, compared with the least explorative calves. With weaning, calves that were highly active had a smaller magnitude change in unrewarded visits leading up to and following weaning than calves that were the least active. Each of the personality traits had a significant association with change in behavior surrounding each of the stressors evaluated, although these associations depended on the type of stressor. These results have implications for how individual calves experience each stressor and therefore individual animal welfare.