Assessment of pain in horses after surgical castration: composition of a pain scale

The objective of this study was to evaluate physiological and behavioural parameters in order to create a composite pain scale for horses after surgical castration. Based on literature several parameters were chosen and tested for their use in a composite pain scale. Two groups of horses (3 in each group) were studied one day preoperatively and three days postoperatively after surgical castration. The horses in the control group received, according the protocol of the University of Utrecht, analgesia preoperatively. The horses in the meloxicam group received analgesia preoperatively and extra analgesia (meloxicam) during the first three days postoperatively. The physiological parameters tested were body temperature, body weight, plasma cortisol concentration, gait, heart rate variability and swelling of the scrotal area. The behavioural parameters consisted of a direct behavioural assessment and a time budget of behaviour, composed of videorecordings of the horses. No important significant differences were found between the meloxicam group and the control group in most of the tested parameters. Almost no significant differences within a group between the base line value and any other day were seen either. This suggests either that the horses of the control group did not experience more pain than the horses in the meloxicam group, or that none of the parameters was sensitive enough to measure the difference between the meloxicam group and the control group. However, only six horses were tested, limiting the results and conclusions that can be drawn from this study. The parameters tested in this study were concluded to need more testing in following studies containing more animals before they can be exluded for sure