Different methods to identify pain after routine surgical castration of equine stallions: composite pain scale, facial expressions, faecal glucocorticoid metabolites and plasma cytokines

Reasons for performing study:

Lack of ‘gold standard’ for pain assessment in horses.

Objectives:

To assess different approaches of quantifying pain in horses. Castration was chosen as a pain model because of its wide clinical relevance. Study design: Exploratory study.

Methods:

51 equine stallions undergoing castration under general anaesthesia were divided in 3 pain-relieving treatment groups: A) single perioperative administration of flunixin (n = 19), B) additional subsequent flunixin administrations (n = 21), D) like A but with intraoperative mepivacaine injections into the spermatic cord (n = 11). All horses were assessed before and 5 times after surgery (up to 44 h) by means of a modified composite pain scale (CPS), a newly developed facial expression pain scale (FEPS), faecal glucocorticoid metabolites (GCMs) and plasma cytokine profiles. The same parameters were measured in a control group C, undergoing general anaesthesia for different nonpainful procedures (n = 6). Data were analysed with nonparametric statistical tests (Wilcoxon, Mann Whitney U).

Results:

Time had an influence on CPS and FEPS scores in treatment groups A, B and D but not in C. Scores of groups A and B were higher compared to groups D and C at 4 (CPS, FEPS) and 8 h (CPS), whereas there was no difference between groups A and B nor between groups D and C. Only in group AB wa there an increase of faecal GCMs 20 h after surgery. GCMs in group AB were higher compared with groups C and D at 32 h. No effects by time or treatment could be identified for the different plasma cytokines.

Conclusions:

CPS and FEPS seem to be able to detect different levels of post castration pain differentiating from possible anaesthesia effect. Additional local anaesthesia of the spermatic cord was associated with lower post surgical pain scores when compared to perioperative flunixin application alone, whereas subsequent applications of flunixin had no obvious effect.