In the April 2018 Regulatory Update, we informed establishments of the importance of refining anaesthesia in rabbits and rodents. We have noticed that these refinements have not been consistently implemented in all project applications. Therefore, we are republishing the segment on this that appeared in the April 2018 update:
Both inhalational and injectable anaesthesia are used frequently for procedures in rabbits and rodents. Inhalational agents can provide safe and effective anaesthesia, and induction is usually straightforward. Injectable anaesthesia is also used commonly, but there are areas where it can be refined which we would like to highlight:
i. The negative effects of α-2 agonists (e.g. xylazine, medetomidine) used in injectable protocols should be reversed using atipamezole once the procedure has been completed. This is, of course, caveated with the requirement to provide appropriate analgesia, since reversal of the anaesthetic effects of the α-2 agent also abolishes any analgesic effects.
ii. Xylazine should be replaced with medetomidine where possible, as medetomidine is a more specific α-2 agonist and is therefore safer, and is more effectively reversed with atipamezole (since the duration of action of medetomidine and atipamezole are similar). This helps to minimise unwanted anaesthetic side effects such as respiratory depression or hypothermia. Using dexmedetomidine rather than xylazine is equally acceptable, but does not offer any significant advantages over medetomidine.
iii. Intraperitoneal (IP) injection of anaesthetics in rodents is associated with a 10-20% failure rate (i.e. some injectate may be administered into the gut, fat, subcutaneous tissue etc.), whereas subcutaneous (SC) dosing appears both more reliable, and better tolerated by rodents and rabbits. Studies by Prof Paul Flecknell (an expert in the field of laboratory animal anaesthesia) and his colleagues have found that a combination of ketamine/medetomidine takes effect just as quickly when given SC compared to IP or intramuscular, and at the same dosages. Therefore, switching from the IP to SC route is recommended, since it is technically easier to perform, is well tolerated by the animal, and seems to reduce the failure rate thus reducing unwanted variability. It is also noted that the intravenous route is also acceptable (and very effective), but the intramuscular route should be avoided due to muscle pain and the risk of necrosis.
Where necessary, applicants are encouraged to seek additional advice from their designated veterinarian regarding these refinements


A number of papers on zebrafish welfare and the 3Rs have recently been published. We recommend that researchers using zebrafish, as well as ethics committees, AWBs and information officers in establishments that keep zebrafish are familiar with these publications:
i. The importance of ethical considerations surrounding fish in research
ii. The impact of invasive procedures on the patterns of movement of zebrafish
iii. Is heightened-shoaling a good candidate for positive emotional behaviour in zebrafish?
iv. The effects of environmental enrichment on survivorship, growth, sex ratio and behaviour in laboratory maintained zebrafish Danio rerio.
v. Welfare challenges influence the complexity of movement: fractal analysis of behaviour in zebrafish