The Association between Heart Rate, Heart Rate Variability, Endocrine and Behavioural Pain Measures in Horses Suffering from Laminitis*

Abstract

The objective of this study was to compare the stress response of horses suffering from laminitis after short- and long-term treatment with the intent to evaluate power spectral analysis of heart rate variability (HRV) for pain monitoring. Data were collected from 19 horses with acute or chronic exacerbating laminitis without known primary disease before and after treatment with non-steroidal anti-inflammatory drugs (NSAID). Recordings were carried out the day after admission to the equine hospital. Measurements were repeated on day 7 of the treatment. The recorded parameters included a clinical orthopaedic index (OLPI: Obel-grade plus hoof tester score), frequency of weight-shifting between contralateral limbs, mean beat-to-beat interval (R-R) duration, standard deviation of continuous R-R intervals, low- (LF) and high-frequency (HF) components of HRV, sympatho-vagal balance (LF/HF), and plasma concentration of cortisol, adrenalin and noradrenalin. The LF represents mainly sympathetic influences on the heart whereas HF is mediated by the parasympathetic tone. Weight-shifting and OLPI decreased significantly with treatment. The LF normalized units (n.u.) decreased after NSAID from 60.41 +/- 21.42 to 51.12 +/- 19.81 and was 49.33 +/- 22.64 on day 7, whereas HF n.u. increased from 35.07 +/- 20.02 to 43.14 +/- 18.30 and was 45.98 +/- 23.00 on day 7. Hormone levels showed no tendency to change with treatment. The OLPI was only correlated with LF/HF, LF and HF (R = 0.57, 0.55 and -0.54 respectively). Significant negative correlations existed between HFn.u. and weight-shifting frequency (R = -0.37), HFn.u. and adrenalin (R = -0.47), and HFn.u. and noradrenalin (R = 0.33). The LFn.u. only correlated positively with adrenalin. Cortisol levels were poorly associated with the other parameters. Determination of the sympatho-vagal influences on cardiac function may offer complementary information for reliable assessment of pain and may represent a valuable alternative method to catecholamine measurements.

Welfare implication of measuring heart rate and heart rate variability in dairy cattle: literature review and conclusions for future research

“…Although, some researchers have suggested the LF component to be mainly of sympathetic origin (Malliani et al, 1991) -in horses it is used as the indicator of sympathetic outflow (Physick-Sheard et al, 2000;Rietmann et al, 2004) -in cattle it does not represent the changes in sympathetic activity (Després et al, 2002;Mohr et al, 2002;Hagen et al, 2005). It has been confirmed, that the LF componentbesides other physiological mechanisms (Malik et al, 1996;Kuwahara et al, 1999) -arises from the interaction of sympathetic and vagal responses (Akselrod et al, 1985;Houle and Billman, 1999) and can be reduced with either sympathetic or parasympathetic antagonists (Cacioppo et al, 1994).…”

“…Effects of technology and of social interactions can be described not only by classical descriptive behavioural observations (e.g. Milmann, 2013;Theurer et al, 2013), but with physiological measures as well (Hopster and Blokhuis, 1994;Rietmann et al, 2004). Most dairy cattle studies have focused on the stress reactions of animals expressed in neuroendocrine changes that are considered to be reliable indicators of stress and pain in livestock species (Dantzer and Mormède, 1983;Matteri et al, 2000;von Borell, 2000).…”

Analgesic effects of butorphanol tartrate and phenylbutazone administered alone and in combination in young horses undergoing routine castration

“…13 Power spectral analysis of heart rate variability, a function of resting autonomic tone, is a helpful technique for measuring stress response to pain; however, sophisticated equipment and specific training are needed for this technique, and it is not widely available. 43 Heart rate and respiratory rate are considered to have moderate sensitivity and specificity as pain indicators, but were not useful for assessment of pain level when used to evaluate signs of pain in horses with experimentally induced synovitis (considered representative of orthopedic pain); similarly, rectal temperature was not considered a sensitive or specific pain indicator in those horses. 44 Gastrointestinal tract sounds were not significantly different among groups in the present study at any time point.…”

Identifying and monitoring pain in farm animals: a review

“…However, HRV as a pain indicator has been poorly investigated. To our knowledge, there is only one study showing that treatment of horses, suffering from laminitis, with NSAID resulted in changes in HRV with an increase of high-frequency components and a decrease of low-frequency components together with less weight shifting behaviours (Rietmann et al, 2004). Trembling resulting probably from activation of the sympathetic nervous system was observed during the first hours following castration in piglets (Hay et al, 2003;Llamas Moya et al, 2008) and in lambs (Molony et al, 2002).…”