Measuring 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. (C) 2015 Elsevier B.V. All rights reserved

Development of the Horse Grimace Scale (HGS) as a Pain Assessment Tool in Horses Undergoing Routine Castration

<div><p>Background</p><p>The assessment of pain is critical for the welfare of horses, in particular when pain is induced by common management procedures such as castration. Existing pain assessment methods have several limitations, which reduce the applicability in everyday life. Assessment of facial expression changes, as a novel means of pain scoring, may offer numerous advantages and overcome some of these limitations. The objective of this study was to develop and validate a standardised pain scale based on facial expressions in horses (Horse Grimace Scale [HGS]).</p><p>Methodology/Principal Findings</p><p>Forty stallions were assigned to one of two treatments and all animals underwent routine surgical castration under general anaesthesia. Group A (n = 19) received a single injection of Flunixin immediately before anaesthesia. Group B (n = 21) received Flunixin immediately before anaesthesia and then again, as an oral administration, six hours after the surgery. In addition, six horses were used as anaesthesia controls (C). These animals underwent non-invasive, indolent procedures, received the same treatment as group A, but did not undergo surgical procedures that could be accompanied with surgical pain. Changes in behaviour, composite pain scale (CPS) scores and horse grimace scale (HGS) scores were assessed before and 8-hours post-procedure. Only horses undergoing castration (Groups A and B) showed significantly greater HGS and CPS scores at 8-hours post compared to pre operatively. Further, maintenance behaviours such as explorative behaviour and alertness were also reduced. No difference was observed between the two analgesic treatment groups.</p><p>Conclusions</p><p>The Horse Grimace Scale potentially offers an effective and reliable method of assessing pain following routine castration in horses. However, auxiliary studies are required to evaluate different painful conditions and analgesic schedules.</p></div

Details of the horses of the control group.

<p>Details of the horses of the control group.</p

Example images and HGS scores.

<p>Example images and associated HGS scores of the same horse pre (a; c) and 8-hours post-procedure (b; d). Images a and b underwent castration; c and d were control animals.</p

The percentage of “not able to score” for each Facial Action Unit identified.

<p>The percentage of “not able to score” for each Facial Action Unit identified.</p

Mean Horse Grimace Scale (HGS) scores pre and 8-hours post-procedure.

<p>HGS scores are presented on the y-axis (±1 SE) for horses undergoing routine castration (A and B), and anaesthesia control group (C) with the pre and 8-hours post-procedure recordings on the x-axis (** P = 0.000).</p

Video cameras position.

<p>The drawing in the middle (b) shows the position of the two HD cameras. Pictures on the left (a) and on the right (c) show frames grabbed from Cam1 and Cam2 respectively.</p

Horse Grimace Pain Scale (HGS).

<p>The Horse Grimace Pain Scale with images and explanations for each of the 6 facial action units (FAUs). Each FAU is scored according to whether it is not present (score of 0), moderately present (score of 1) and obliviously present (score of 2).</p

Breed and mean age of the stallions of the two treatment groups.

<p>Breed and mean age of the stallions of the two treatment groups.</p

Mean Composite Pain Scale (CPS) scores pre and 8-hours post-procedure.

<p>CPS scores are presented on the y-axis (±1 SE) for horses undergoing routine castration (A and B), and anaesthesia control group (C) with the pre and 8-hours post-procedure recordings on the x-axis (** P = 0.000).</p