There is no need for overnight fasting of rats in regulatory toxicology studies.

For many years overnight fasting of rats before the collection of clinical pathology blood samples and necropsy has been a common procedure in toxicological studies for regulatory purposes. The fasting was thought to minimize the intragroup variability for clinical pathology and organ weights. However, depriving rats of food overnight will impact animal welfare by interfering with the general metabolism and may result in physiological and behavioural changes.