Review articleMeasuring heart rate variability in horses to investigate the autonomic nervous system activity - Pros and cons of different methods

Power spectrum analysis of heart rate variability (HRV) may provide insight into the mental state of the animal held in restricted specific experimental conditions. Determining inter-beat-interval (IBI) variations is one way to measure changes in autonomic nervous system (ANS) activity in horses. An imbalance between the sympathetic and parasympathetic nervous system can indicate pain or stress, for example, if other stimuli such as excitement or fear can be eliminated. However, the outcomes of a HRV analysis hinge on the accuracy of the IBI measurements and the analysis methods. Applied measurement techniques, analysis methods and even frequency bands for power spectrum analysis differ considerably across studies. Hence, the measurement of heart rate variability in horses is handled rather inconsistently and results from different studies are not entirely comparable. The current review presents an overview of the technical issues of HRV analyses, then discusses recent HRV measurements in horses and finally gives recommendations for standardised IBI-measurement and HRV analysis in horses.