Heart rate and heart rate variability during a novel object test and a handling test in young horses.

This research article studies the temperamental traits of young horses by using heart rate (HR) and heart rate variability (HRV) measures during novel object and handling tests. The results suggest that these measures might highlight differences in the temperament of horses that have received additional training compared to those that haven’t, and could indicate the level of emotionality in horses.

Study Design and Participants

• The researchers used 41 young Dutch Warmblood horses in this study.
• From the age of 5 months, half of these horses received additional training while the other half did not.
• These horses were injected at 9, 10, 21, and 22 months of age with novel object and handling tests.
• Herald rate (HR) and HRV measures were taken during these tests.

Test Method and Calculations

• The mean heart rate and two heart variability indices—the standard deviation of beat-to-beat intervals (SDRR) and root mean square of successive beat-to-beat differences (rMSSD)—were calculated during the tests.
• To determine the response to the tests, these measures were then compared to baseline measures.

Findings

• The researchers observed a significant increase in mean HR and decrease in HRV measures in the horses during both tests at all ages.
• This change suggests that the balance of the autonomic nervous system’s function shifted towards sympathetic dominance—associated with the body’s “fight or flight” response—during the tests.
• This change in HR and HRV was more pronounced in horses that had not received additional training, particularly during the novel object test.
• The increase in mean HR was found to be greater than could be explained by physical activity alone.
• The increase in non-motor HR—which is the additional increase in HR beyond what’s expected for physical activity—was also more prominent in untrained horses. This suggests it may be related to the level of emotionality in the horses.
• The HR variables remained consistent across different ages and within the second year of life, implying individual consistency in these HR measures.

Conclusions

• The researchers concluded that mean HR and HRV measures can effectively quantify specific aspects of a horse’s temperament.
• These HR measures could potentially be used as indicators of a horse’s emotional state or temperament during certain tests or situations.