Pain-related facial expressions, heart rate variability and operator-assessed procedural ease during transvaginal follicular aspiration in mares: effect of procedure, sedation and butylscopolamine bromide - metamizole.

This study evaluated the effect of stock restraint, mare preparation, ovarian manipulation and/or puncture, sedation and butylscopolamine bromide-metamizole on Heart Rate Variability (HRV), facial expressions and operator - assessed procedural ease during ovum pick up (OPU) in mares. Six healthy adult mares were subjected to the three experimental protocols in a randomized crossover design: sham OPU without sedation, sham OPU with sedation and regular OPU with sedation. Each experimental protocol consisted of five sequential phases: baseline assessment, post-sedation (or saline) assessment, mare preparation, ovarian manipulation or follicular puncture before butylscopolamine bromide-metamizole administration, and a final ovarian manipulation or follicular puncture after butylscopolamine bromide-metamizole administration. HRV, pain-related facial expressions, operator-assessed procedural ease, and the number of rectal peristaltic waves recorded in real time during ovarian manipulation were evaluated. HRV data were analysed using repeated-measures general linear models, whereas facial expression data were analysed using generalized linear mixed models. Operator-assessed procedural ease and peristaltic waves were analysed using paired and unpaired tests, as appropriate. HRV parameters differed primarily according to sedation status, with no additional changes associated with follicular puncture. Non-sedated mares showed higher heart rate (HR) and sympathetic nervous system index (SNSi), and lower parasympathetic nervous system index (PNSi), than sedated mares. Butylscopolamine bromide-metamizole reduced peristaltic waves from 2.2 ± 1.5 to 0 waves (p < 0.012) in non-sedated mares and sedation reduced peristaltic waves from 2.2 ± 1.5 to 0.4 ± 0.9 waves (p = 0.041). The frequency of pain-related facial expressions increased during ovarian manipulation in non-sedated mares compared with sedated mares (p < 0.05), whereas follicular puncture itself did not further increase this parameter. In conclusion, HRV showed limited utility for pain assessment, due to pharmacological effects, whereas facial expressions provided a sensitive identification of discomfort, particularly during ovarian manipulation and puncture. Butylscopolamine bromide-metamizole facilitated ovarian handling and reduced peristaltic activity and discomfort. Follicular puncture did not appear to increase pain beyond ovarian manipulation. These findings support the use of behavioral parameters to evaluate pain and highlight the need to refine analgesic protocols to improve animal welfare during OPU.