Location: Livestock Behavior ResearchTitle: Measuring disbudding pain in dairy calves using nonlinear measures of heart rate variability Author
|Byrd, Christopher - Purdue University|
|Craig, Bruce - Purdue University|
|Radcliffe, John - Purdue University|
|Lay, Jr, Donald - Don|
Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/13/2019
Publication Date: N/A
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: Hot-iron disbudding is a common, but painful, procedure for dairy calves in the United States and has been shown to alter autonomic function in the period immediately following the disbudding procedure. The purpose of this study was to evaluate whether pain-related stress resulting from disbudding was long-lasting and could be measured using heart rate variability, a proxy measure of autonomic nervous system (ANS) function. Twenty-five female Holstein calves (4 to 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 was collected on d -1, 0, 1, 3, and 5 of the experimental procedure, with disbudding taking place on d 0. Additionally, blood was collected via jugular catheter at – 0.5, +0.5, +1, +2, +4, +8 and +24 h relative to disbudding for cortisol analysis. Plasma cortisol concentrations for NoMED calves were greater (45.9 ± 7.6 ng/mL) at +0.5 h post-disbudding compared to MED (11.4 ± 4.8 ng/mL; P = 0.03) and SHAM calves (10.5 ± 3.7 ng/mL; P = 0.003). Calves in the SHAM treatment group spent more time in an active posture (32.7 ± 2.6 %) than MED (21.2 ± 2.8 %; P = 0.02) and NoMED (22.1 ± 2.8 %; P = 0.03) calves. Average R-R interval (RR) was lower (P = 0.004) and the short-term detrended fluctuation analysis scaling exponent (DFA a1) was greater (P = 0.04) in MED calves compared to SHAM calves. In conclusion, RR and DFA a1 were altered in MED calves compared to SHAM calves, indicating increased stress as a result of the disbudding procedure. Calves in the NoMED group displayed an intermediate HRV response when compared to MED and SHAM calves, however numeric temporal changes to RR and DFA a1 in NoMED calves clearly mirrored MED calves instead of SHAM calves. These results may indicate that calves in the MED group also experienced pain-related stress as a result of the disbudding procedure. Future research on this topic should address additional potential confounding factors, such as the influence of the ANS’s role in wound healing, that may prohibit HRV measurement as an indicator of disbudding pain severity.