Abstract
Simple SummaryIn the United States, castration is a common husbandry procedure utilized in the cattle industry. Despite castration being painful, it is commonly performed without the use of analgesia, one reason being the lack of available approved analgesics in the United States for use in alleviating pain associated with castration in cattle. Additionally, if pain mitigation is used, it is more often provided to older animals as there is a notion that younger animals experience pain to a lesser degree than older ones. The aim of this study was to characterize physiological responses to unmitigated surgical castration in calves of varying ages in terms of cortisol concentration, heart rate variability, and changes in eye temperature. Overall, our results indicate that the measured physiological responses to castration differed between age groups and changed over time post-castration. Younger calves showed a different response pattern than older calves for many of the variables measured suggesting that the response to castration-induced pain may be age-specific. For example, the youngest calves had lower cortisol and average eye temperature as compared to the oldest calves. Additionally, many variables showed a differential response to castration-induced pain, as compared with simulated castration, thus suggesting physiological indicators that could be targeted in future development and validation of analgesics for alleviation of pain associated with castration in cattle.The objective was to characterize physiological responses to unmitigated surgical castration in calves of varying ages. Thirty male Holstein calves of three ages [<6 w (6W); 3 m (3M); 6 m (6M); n = 10] underwent a simulated castration treatment (SHAM) followed 24 h later by castration (CAST). For both treatments, heart rate variability, eye temperature, and cortisol were measured over time from treatment to specified end points to capture the acute response period. Interactions between treatment and age (p = 0.035) and time and age (p < 0.001) were noted for cortisol. The 6W calves had lower cortisol compared to 6M calves at SHAM and CAST. Cortisol of 6W calves decreased from peak to pre-treatment levels faster than 6M calves. An interaction between time and age was reported in squared differences of inter-beat-intervals (RMSSD; p = 0.02) and high-frequency power (HFP; p = 0.05), whereby both responses decreased in 6W calves during the sampling period which was not seen in 3M and 6M calves. Average eye temperature (AET) differed by age (p = 0.0018) whereby 6W calves had lower AET than 6M calves (p = 0.0013) regardless of treatment and time. The findings suggest that responses to unmitigated surgical castration seem to be mediated by the autonomic nervous system in an age-related manner.
Highlights
Bovine castration is a painful procedure typically performed without analgesia in the United States [1,2], stakeholder groups do encourage the adoption of techniques to minimize pain and distress associated with the procedure [3,4,5]
During SHAM, cortisol concentration decreased from peak levels to pre-treatment levels within 50 min post-treatment in 6 weeks (6W) calves, whereas for 3 months (3M) and 6 months (6M) calves, cortisol concentrations returned to baseline values 120 min after the treatment (Table 1)
During CAST, cortisol concentrations for 6W and 3M calves decreased from peak levels to pre-treatment levels within 120 min after treatment, whereas for 6M calves, cortisol concentrations returned to baseline values 240 min after treatment (Table 2)
Summary
Bovine castration is a painful procedure typically performed without analgesia in the United States [1,2], stakeholder groups do encourage the adoption of techniques to minimize pain and distress associated with the procedure [3,4,5]. One of the limitations with providing pain mitigation for castration in the United States is the lack of available. FDA-approved drugs to control pain associated with castration [1,2,6]. There are several approved analgesics for use to control pain in cattle available in other countries, in the United States, there is only one approved drug authorized for this use (e.g., transdermal flunixin meglumine, for pain related to interdigital phlegmon, i.e., foot rot; [7]). Castration is generally considered more painful in older calves, studies examining physiological and neuroendocrine responses to pain as a function of age are lacking. There are several physiological measures that can be used to measure the activation of these systems in response to a painful procedure such as castration in cattle.
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