Overnight fasting of rats before collection of clinical pathology blood samples and necropsy has been common in toxicological studies for many years. This week, the practise, intended minimize the intragroup variability for clinical pathology and organ weights, has been brought into question by a team based at Charles River Den Bosch, Netherlands. The team evaluated 92 OECD 422 studies (Combined Repeated Dose Toxicity Study with the Reproduction/Developmental Toxicity Screening Test) in which roughly half were fasted before collection and the other half were not. Although some differences between fasted and non-fasted states exist, these were considered to be of little consequence. The authors propose that fasting is not required, and that the most ethical approach would be to continue feeding all rats ad libitum, to minimize physiological changes in these animals, to reduce variability, improve animal welfare and thereby improve the scientific value of study results.

https://www.sciencedirect.com/science/article/abs/pii/S0300483X2400218X?dgcid=coauthor