Using the mouse grimace scale and behaviour to assess pain in CBA mice following vasectomy

Mice used in biomedical research should have pain reduced to an absolute minimum through refinement of procedures or by the provision of appropriate analgesia. Vasectomy is a common and potentially painful surgical procedure carried out on male mice to facilitate the production of genetically modified mice. The aim of our study was to determine if 0.05 mg/kg buprenorphine would ameliorate pain associated changes following abdominal vasectomy and to determine if the mouse grimace scale is an appropriate tool for the assessment of pain in this model. Eight male CBA mice underwent abdominal vasectomy as part of a genetically modified mouse-breeding programme. Here we assessed pain using a previously validated behaviour-based method and the mouse grimace scale. All mice received buprenorphine (0.05 mg/kg s.c.) pre-surgery. Behaviour and grimace scores were compared between baseline (pre-surgery), 30 min, 5 h, 24 h and 25 h post surgery. Following 24 h post-op, all mice were administered 5 mg/kg meloxicam (s.c.) as additional analgesia. Significant increases in specific pain behaviours and mouse grimace scale score were found 30 min post surgery. At 5 h post surgery, scores were returning to baseline levels. Frequency of rearing was significantly decreased at both 30 min and 5 h post surgery compared to baseline, demonstrating a longer lasting change in normal exploratory behaviour. Buprenorphine (0.05 mg/kg) was ineffective at ameliorating these pain-associated changes in CBA mice and should be considered inadequate at this dose. By 24 h post surgery, pain associated behaviours, grimace scale and rearing had all returned to baseline levels. There was no change in pain behaviours or MGS following administration of meloxicam indicating that an additional dose of meloxicam does not appear to offer benefit at this point. Using the mouse grimace scale to assess pain in mice, appeared to be effective in the immediate post vasectomy period in CBA mice demonstrating the same duration of increased score as the pain associated behaviours.