Unmitigated Surgical Castration in Calves of Different Ages: Electroencephalographic and Neurohormonal Findings

Abstract

Castration is a common management procedure employed in North American cattle production and is known to cause a pain response. The present study was designed to investigate the effect of unmitigated surgical castration on the electroencephalography (EEG) responses and plasma substance P (SP) concentrations in calves of different ages under the same experimental conditions. Thirty male Holstein calves in three age categories [<6 weeks (6W); 3 months (3M); 6 months (6M); 10 calves per age group] were used in the study. Calves were subjected to a simulated castration session (SHAM) followed 24 h later by surgical castration (CAST) without analgesia. An EEG analysis was performed before the procedure (i.e., baseline), at treatment, and 0–5, 5–10, and 10–20 min post-treatment for both SHAM and CAST, respectively. Blood samples were collected immediately prior to both treatments (time 0) and again at 1, 2, 4, 8, and 12 h after both treatments. The EEG results showed a three-way interaction between treatment, age, and time for delta and beta absolute power, beta relative power, total power, and median frequency (p = 0.004, p = 0.04, p = 0.04, p = 0.03, and p = 0.008, respectively). Following CAST, EEG total power decreased, and median frequency increased relative to SHAM in 6W and 3M calves only following treatment. For 6W and 3M calves, delta and beta absolute power increased at CAST and at later time points relative to SHAM. Marginal evidence for two-way interactions was noted between time and treatment and between age and treatment on the concentration of SP (p = 0.068 and p = 0.066, respectively). Substance P concentrations decreased in CAST treatment compared to SHAM at the later times (8 h: p = 0.007; 12 h: p = 0.048); 6W calves showed lower SP concentration at CAST relative to SHAM (p = 0.017). These findings indicate variation in EEG responses and in SP concentrations following unmitigated surgical castration in calves and that these responses may be age specific. These EEG findings have implications for supporting the perception of the pain associated with surgical castration in young calves and emphasize the urgency of pain mitigation strategies during routine husbandry practices such as castration, as typically implemented in North American cattle management.

Unmitigated Surgical Castration in Calves of Different Ages: Cortisol Concentrations, Heart Rate Variability, and Infrared Thermography Findings

“…This study characterized the acute physiological responses to unmitigated surgical castration in calves of varying ages, specifically cortisol concentration, heart rate variability, and changes in eye temperature, with the ultimate goal of supporting pain mitigation strategies for routine management practices like castration. Additional outcomes are reported in Bergamasco et al [ 21 ], a companion paper that can be referred to for further information. Despite the fact that surgical castration is a painful procedure having both acute and chronic impacts, the use of pain control is not routinely practiced in the United States [ 1 , 2 ].…”

“…Research reported here was part of a large study reported in a companion paper [ 21 ] and therefore the experimental design and sampling methods are as described in that study. This research was approved by the Institutional Animal Care and Use Committee at Kansas State University (Protocol #2831).…”

“…Jugular catheters were placed following the methods of Bergamasco et al [ 21 ]. In brief, the area over the jugular vein was clipped and 70% isopropyl alcohol and povidone iodine swabs were used to disinfect the area.…”

“…Both SHAM and CAST procedures were conducted between 0600 and 1030 on each processing day at 45 min intervals. Each calf was restrained in the chute with head movement limited by a halter drawn close to a table attachment (For-most Livestock Equipment, Hawarden, IA, USA) for approximately 30 min in order for experimental procedures to be completed; additional measurements to what is reported in this manuscript were taken [ 21 ]. The same operator performed all surgical procedures.…”

“…For both treatments, the scrotum was washed with chlorhexidine disinfectant. The SHAM and CAST experimental procedures followed Bergamasco et al, [ 21 ]. For SHAM, the testes were firmly grasped, and ventral traction was applied for approximately 20 s. For CAST, the lower one-third of the scrotum was cut with a sharp, disinfected scalpel and the testes and spermatic cords were exteriorized followed by manual traction until the spermatic cord and connective tissue ruptured.…”