CO2 euthanasia is acceptable only when it is done with a validated delivery system and chamber, under IACUC-approved guidance, to ensure the death is humane and any distress is minimized. Using a validated flow rate and chamber means the equipment and protocol have been tested to reliably render the animal unconscious before significant suffering occurs, and the exposure is controlled to avoid unnecessary stress. Following IACUC guidance brings formal oversight, trained personnel, and review of the protocol, including consideration of alternatives if CO2 is not the best option for a particular animal or situation. Proper setup, monitoring, and the option to choose other methods when appropriate are essential to upholding welfare standards.

Intraperitoneal injections in mice are positioned lower on the abdomen to minimize injury to internal organs. The cecum is a large, easily punctured part of the gut that sits in the lower abdomen, and approaching from the right side keeps the needle away from it. Puncturing the cecum can release intestinal contents into the peritoneal cavity, causing inflammation or infection and compromising the procedure as well as the study. So, choosing the right-side lower quadrant makes the injection safer by reducing the risk of hitting the cecum. The other ideas listed don’t directly address this particular injury risk, which is why this site is preferred.

Standard operating procedures in a mouse facility are formal written instructions that define exactly how routine and welfare-critical tasks are performed so every team member does them the same way. In practice, this means SOPs cover how mice are housed, fed, and watered; how they are handled and restrained; how health monitoring, disease prevention, analgesia, anesthesia, and euthanasia are performed; how breeding, colony management, and procedures for transfers or experimental interventions are conducted; how sanitation, disinfection, equipment maintenance, and waste disposal are managed; and how records are kept for traceability and regulatory review. The goal is to ensure animal welfare and compliance with laws and guidelines, such as IACUC oversight and GLP standards, and to support reproducibility of results. They are mandatory and routinely reviewed and updated, with training tied to their content. They are not primarily about financial records, do not determine the genetic background, which is about strains and genetics rather than procedural instructions.

Oral gavage is the technique of delivering a precise volume of liquid directly to the stomach by threading a gavage needle through the mouth and down the esophagus. This method is used to ensure the substance reaches the stomach for accurate dosing in mice and other small animals, rather than relying on absorption from the oral cavity or alternative routes. A gavage needle or soft feeding tube is used, and proper restraint and technique are essential to guide the tip to the stomach and avoid injury or misplacement that could lead to aspiration. The volume is typically calculated based on body weight and the protocol being followed. The other options describe different administration routes or purposes: delivering fluid into the bloodstream, into the peritoneal cavity, or inhaling anesthetic gas.