Analgesic interventions in surgically castrated beef calves: impacts on biomarkers, thermography, and growth performance under tropical conditions.

Castration is common in beef cattle for reproductive and management purposes, but it causes pain and stress, raising welfare concerns. The adoption of perioperative anesthesia and analgesia remains uneven in tropical low- and middle-income settings, where infrastructure, costs, and weak enforcement limit its application. This study aimed to evaluate the effects of different analgesic protocols on physiological stress markers and growth performance in beef calves raised under tropical conditions in Colombia. Forty-two intact Blanco Orejinegro (BON) calves were randomly assigned to three protocols: spermatic cord block with lidocaine plus tolfenamic acid (T1), low epidural anesthesia with lidocaine plus tolfenamic acid (T2), or tolfenamic acid alone (T3). All calves underwent closed surgical castration. Physiological and welfare indicators were assessed through pulse rate variability (PRV), hematological parameters, serum haptoglobin and cortisol concentrations, and infrared thermography (IRT) of the scrotal area at defined intervals, whereas growth performance was evaluated by average daily gain (ADG). Statistical analyses included ANOVA and nonparametric tests when assumptions were violated, with multiple comparisons corrected via Tukey's test or Dunn's test. No significant differences were found among the protocols for the PRV, hematological parameters, cortisol, haptoglobin, IRT, or ADG. In contrast, significant temporal effects were observed, with cortisol decreasing at 48 h, haptoglobin peaking at 48-72 h, and IRT values increasing between 24 and 48 h postcastration. These results indicate that the time after castration, rather than the analgesic protocol, was the primary driver of physiological responses.