Serial blood collection in anaesthetised rats: Enhancing animal welfare without the need for jugular vein catheterisation.

Serial blood collection is a key requirement for pharmacological and toxicological studies in rodents, but existing approaches such as tail vein, retro-orbital, or catheter-based sampling are constrained by limited sample volume, variability, and welfare concerns. We developed a percutaneous technique for serial blood sampling from the external jugular vein in male Wistar rats under isoflurane anaesthesia. The method was evaluated over 14 days by monitoring body weight, behaviour, haematological and clinical chemistry parameters in a preclinical safety study at a No-Observable-Adverse-Effect-Level dose setting. Rats tolerated repeated sampling without distress, skin lesions, or behavioural abnormalities. Isoflurane induction was rapid and uneventful, and blood samples (0.5-1 ml) were consistently obtained within 2 min. Body weight changes were minimal across sessions (1.2 % after the first to 0.2 % after the sixth), indicating procedural adaptation. Haematological values remained within reference ranges, with only a significant reduction in RDW-CV, while biochemical parameters including AST, CK, and lipids showed no significant alterations; minor, non-adverse trends included reduced ALT (p < 0.041) and non-significant cholesterol and minimal non-significant increases in plasma creatinine. This study establishes repeated percutaneous jugular vein puncture as a minimally invasive, welfare-compliant, and reliable method for longitudinal blood sampling in anaesthetised rats without catheterisation, supporting robust preclinical research.