Abstract
A scale with robust statistical validation is essential to diagnose pain and improve decision making for analgesia. This blind, randomised, prospective and opportunist study aimed to develop an ethogram to evaluate behaviour and validate a scale to assess acute ovine postoperative pain. Elective laparoscopy was performed in 48 healthy sheep, filmed at one preoperative and three postoperative moments, before and after rescue analgesia and 24 hours after. The videos were randomised and assessed twice by four evaluators, with a one-month interval between evaluations. Statistical analysis was performed using R software and differences were considered significant when p <0.05. Based on the multiple association, a unidimensional scale was adopted. The intra- and inter-observer reliability ranged from moderate to very good (intraclass correlation coefficient ≥ 0.53). The scale presented Spearman correlations > 0.80 with the numerical, simple descriptive, and visual analogue scales, and a correlation of 0.48 with the facial expression scale. According to the mixed linear model, the scale was responsive, due to the increase and decrease in pain scores of all items after surgery and analgesic intervention, respectively. All items on the scale demonstrated an acceptable Spearman item-total correlation (0.56-0.76), except for appetite (0.25). The internal consistency was excellent (Cronbach's α = 0.81) and all items presented specificity > 0.72 and sensitivity between 0.61-0.90, except for appetite. According to the Youden index, the cut-off point was ≥ 4 out of 12, with a diagnostic uncertainty zone of 4 to 5. The area under the curve > 0.95 demonstrated the excellent discriminatory capacity of the instrument. In conclusion, the Unesp-Botucatu pain scale in sheep submitted to laparoscopy is valid, reliable, specific, sensitive, with excellent internal consistency, accuracy, discriminatory capacity, and a defined cut-off point.
Highlights
The lack of valid and reliable instruments to recognise and quantify pain in farm animals compromises their welfare state and limits the use of analgesics in these species [1,2,3,4]
The study was approved by the Ethics Committee on Animal Use from the School of Veterinary Medicine and Animal Science, São Paulo State University (Unesp), Botucatu, São Paulo, Brazil, under protocol 0027/ 2017 and followed the recommendations of ARRIVE [44] adapted to the experimental design
This methodology was followed in the current study; an ethogram was constructed during the preoperative period when animals were supposedly devoid of pain, followed by the postoperative period when animals probably had severe pain, followed by rescue analgesia for pain reduction and reassessment after 24 hours
Summary
The lack of valid and reliable instruments to recognise and quantify pain in farm animals compromises their welfare state and limits the use of analgesics in these species [1,2,3,4]. The sheep species is an experimental model for humans due to its similarity in size and weight. Pigs followed by sheep are more commonly used than dogs and non-human primates as non-rodent models for research and teaching [8,9]. Actigraphy can be used to monitor sheep activity from a distance, this method requires specific equipment [15]. Other physiological measures, such as hair cortisone concentration [16], heart rate variability [17], blood pressure, ocular and rectal temperature, electromyography, and electroencephalography are not clinically feasible and some require physical restraint [18]
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