What type of blood collection method is typically discouraged because of its painful nature in rodents?

The retroorbital blood collection method is typically discouraged in rodents primarily due to the potential for pain and injury it can cause. This technique involves piercing the membrane behind the eye to obtain blood, which not only carries a risk of significant discomfort to the animal but can also lead to complications such as damage to the eye or surrounding structures. The sensitivity of the ocular region makes this method particularly concerning in terms of animal welfare, leading to its limitation or avoidance in many institutional animal care protocols.

In contrast, while other methods such as facial vein collection or lateral saphenous collection may be less invasive and generally accepted, the retroorbital method's unique position as a source of pain and distress stands out. This understanding aligns with the principles of humane treatment and the guidelines of the IACUC, which prioritize minimizing pain and distress in research animals.