Assessment of post-operative pain by nest complexity scoring in mice

Abstract

Pain in laboratory mice is difficult to detect with conventional methods as mice do not obviously show symptoms of mild to moderate pain. Here we investigated the feasibility and reliability of nest building performance under various conditions as a method to detect mild to moderate post-operative pain in laboratory mice and aimed to standardise this method for the routine use.
Female mice were randomly allocated into control (anaesthesia +/- analgesia) and surgery groups (minor laparotomy +/- analgesia) in two housing conditions. Animals were observed before (baseline) and after treatments (experiment). The nests were scored at seven time points with a numeric scoring system and latency of nest building was measured as well as consumption of the nesting material.
Baseline nest scores were always higher than experimental scores and a reliable discrimination was found at three to nine hours after the start of the measurements. A clear graduation in nest complexity was seen after experiments, with higher nest scores in control groups than in surgery groups. Latency in the baseline was always shorter than in the experiment and latency in control groups was shorter than in surgery groups during experimental measurements. Pair housed mice had a slightly higher consumption of the nesting material than individually housed mice.
In conclusion, scoring of nest complexity at three to nine hours after laparotomy was useful to identify post-operative impairment, caused by moderate pain.