Short communication: Assessment of disbudding pain in dairy calves using nonlinear measures of heart rate variability

Authors: BYRD, CHRISTOPHER - Purdue University; CRAIG, BRUCE - Purdue University; Eicher, Susan; RADCLIFFE, JOHN - Purdue University; Lay Jr, Donald

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/13/2019
Publication Date: 7/10/2019
Citation: Byrd, C.J., Craig, B., Eicher, S.D., Radcliffe, J., Lay Jr, D.C. 2019. Short communication: Assessment of disbudding pain in dairy calves using nonlinear measures of heart rate variability. Journal of Dairy Science. 102(9):8410-8416. https://doi.org/10.3168/jds.2018-15948.
DOI: https://doi.org/10.3168/jds.2018-15948

Interpretive Summary: Removal of the horn buds is a common, but painful, procedure for dairy calves in the United States, where 94% of operations perform some sort of disbudding or dehorning procedure. Approximately 50% of calves born annually are disbudded with a hot iron dehorner, and of those, approximately 70% go without analgesic or anesthetic treatment for management of pain. The reluctance to provide disbudding pain management in dairy calves is often cited as a matter of cost to the producer, but recent stakeholder surveys have also reported a belief that young calves exhibit decreased sensitivity to pain due to an immature central nervous system and that disbudding pain is relatively short lasting; although, previously published evidence has shown alterations to physiology and behavior can be long-lasting. Heart rate variability is a common, non-invasive, proxy measure of the stress response and has been used in several studies focused on evaluating the stress response of dairy cattle to common on-farm stressors. As a result, changes to the interval between adjacent heart beats over a period of time can be used as an indicator of the stress response.The objective of this study was to evaluate temporal changes to heart rate variability for 5 days post-disbudding using heart rate variability. We hypothesized that calves disbudded without pain mitigation would exhibit evidence of increased stress as a result of hot-iron disbudding compared to calves that were disbudded with pain mitigation or sham disbudded. In response to disbudding, calves disbudded without analgesics had higher plasma cortisol concentrations (stress hormone) than calves on analgesics and calves that were not disbudded and spent less time in an active posture. Calves that received analgesics also spent less time in an active posture and exhibited less heart rate variability. These results may indicate that calves on analgesics also experienced pain-related stress, compared to calves not on analgesics, as a result of the disbudding procedure. Therefore, a single dose of analgesic may not be sufficient for mitigating disbudding pain. However, future research should rule out potential confounding factors such as the role of the nervous system in wound healing that may impact the use of heart rate variability as an indicator of disbudding pain severity in dairy calves.

Technical Abstract: The purpose of this study was to evaluate whether pain-related stress caused by disbudding could be detected using nonlinear measures of heart rate variability (HRV). Twenty-five female Holstein calves (4–7 wk of age) were randomly assigned to 1 of 3 treatments: (1) sham disbud (SHAM; n = 9), (2) disbud with lidocaine–meloxicam pain mitigation (MED; n = 8), or (3) disbud without pain mitigation (NoMED; n = 8). Heart rate variability (sample entropy, percentage determinism, percentage recurrence, or mean length of diagonal lines in a recurrence plot) was recorded on d -1, 0, 1, 3, and 5 relative to the experimental procedure, with disbudding taking place on d 0. The short-term detrended fluctuation analysis scaling exponent was greater in MED calves than in SHAM calves, indicating a greater stress response to the disbudding procedure regardless of pain mitigation. These results indicate that calves in the MED group may have experienced pain-related stress as a result of the disbudding procedure. The remaining nonlinear HRV measures did not differ by treatment. Future research on this topic should address additional potential confounding factors, such as the effect of pain-mitigating drugs on autonomic function or the influence of the autonomic nervous system on wound healing, that may prohibit HRV measurement as an indicator of disbudding pain severity.