Effects of the administration of the xylazine or dexmedetomidine on plasma concentration of cortisol and substance d in calves undergoing disbudding and simulated disbudding

The aim of this study is to compare the behavior of cortisol and substance P plasma concentrations in dairy calves undergoing disbudding or simulated disbudding, after administration of xylazine, dexmedetomidine or placebo. Moreover this work evaluates the efficacy of dexmedetomidine versus xylazine during disbudding, in order to increase the number of analgesic molecules available for the bovine specie. The protocol for this study was approved by the Institutional Ethical Committee for Animal Care at University of Milan (protocol No. 28/2011. This study was a blinded, randomized, prospective and placebocontrolled trial, performed in healthy calves. Cortisol and substance P were analized in plasma in 60 calves divided in 6 groups of 10 animals and submitted to disbudding (BUD) or simulated disbudding (SIM) after the administration of a placebo (Groups 1 PLA-BUD and Group 2 PLA-SIM), 0.2 mg/kg b.w. xylazine (Groups 3 XYL-BUD and Group 4 XYL-SIM) or 5 μg/kg b.w. dexmedetomidine (Groups 5 DEX-BUD and Group 6 DEXSIM). Blood samples were collected for each group 30 minutes before disbudding or simulated disbudding (basal), within 5 minutes from the procedure (T0), 20 minutes (T1) and 1, 2, 3 and 4 hours after the procedure (T2, T3, T4 and T5 respectively). Cortisol plasma concentration increased at T0 and T1 especially in calves of groups 1 PLA-BUD, 2 PLA-SIM, 3 XYL-BUD; a little increase was detected also in group 4 XIL-SIM at T1. Substance P was higher only at T1 in group 1 PLA-BUD. Substance P has been suggested as biomarker of pain in assessment of analgesic efficacy instead of cortisol, that can be influenced by many stressors as trasport, manipulation, or alpha-2 agonist administration. Also in our study, substance P seems to be a better indicator of pain than cortisol because cortisol was influenced in groups 1 PLA-BUD, 2 PLA-SIM, 3 XYL-BUD and 4 XIL-SIM by stress caused by handling or hemodynamic and respiratory distress induced by xylazine administration. Even if society concerrn regarding animal welfare and suffering has grown up exponentially, there are really few sedatives or anestetics registered to alleviate pain during zootecnical mutilation in food animals, the present study proposes to consider the employment of dexmedetomidine, a new effective alpha-2agonist in calves submitted to disbudding.