Oral gavage dose volume is the amount of liquid delivered to the stomach of a laboratory animal in a single gavage administration, expressed relative to the animal's body weight in millilitres per kilogram (mL/kg). For both mice and rats, the widely used good-practice volume for a single administration is 10 mL/kg body weight. At this rate a 25 g mouse receives about 0.25 mL, and a 250 g rat receives about 2.5 mL. Lower volumes are preferred whenever the concentration of the dose formulation allows, because smaller volumes reduce gastric distension and animal stress.
The 10 mL/kg figure is a widely used reference point in institutional animal ethics guidance and in published good-practice guides for aqueous formulations dosed to non-fasted animals. It is treated as a practical working volume rather than a target: the aim is to deliver the required dose in the smallest volume that is technically and physiologically reasonable. Some published guidance permits higher volumes with explicit justification. The good-practice guide of Diehl et al. (2001), for example, lists possible maxima of around 40 mL/kg for rats and 50 mL/kg for mice, while noting that such large volumes can overload the stomach, so institutional practice generally works to the lower 10 mL/kg figure. Where a compound is soluble enough to concentrate the dose, a volume of 5 mL/kg or lower is generally preferable.
To convert the guideline into an actual volume, multiply body weight in kilograms by the volume rate. A 20 g mouse (0.020 kg) at 10 mL/kg receives 0.20 mL, or 200 microlitres. A 30 g mouse receives 0.30 mL. A 200 g rat receives 2.0 mL and a 400 g rat receives 4.0 mL. Because body weight varies between individual animals, gavage volumes should be calculated per animal from a current weight rather than applied as a fixed volume across a cohort.
Fasting state and species affect how much can be given. In non-fasted animals the stomach already holds food, and 10 mL/kg remains the usual good-practice volume. Turner et al. (2011) give a wider range of 10 to 20 mL/kg for rats, and removing food for a few hours before dosing is sometimes used to allow a larger gavage volume. Volumes above the usual figure should only be used where the institutional protocol explicitly approves them. Exceeding the approved volume can cause gastric distension, reflux into the oesophagus, altered gastric emptying, and stress responses that may confound study results.
Repeated and chronic dosing generally warrants more conservative volumes than a single acute administration. When animals are gavaged daily over days or weeks, the cumulative burden of large volumes can increase the risk of oesophageal and gastric irritation, so good practice for chronic studies favours the lower part of the range. The approved volume for any study is set by the institutional animal ethics committee (AEC in Australia, IACUC in North America), and that approval, together with the relevant OECD test guideline for the study type, is the authoritative source.
Key Points
- Widely used good-practice volume for a single oral gavage is 10 mL/kg body weight in both mice and rats
- A 20 g mouse at 10 mL/kg receives 0.20 mL (200 microlitres); a 250 g rat receives 2.5 mL
- Calculate volume per animal from a current body weight, not as a fixed volume across a cohort
- Prefer lower volumes (5 mL/kg or below) where the formulation can be concentrated
- Published good-practice maxima run higher (around 40 mL/kg for rats, 50 mL/kg for mice per Diehl et al. 2001) but are used only with explicit justification
- Some guidance allows up to 20 mL/kg in rats, but only where the institution explicitly approves it
- Chronic and repeat dosing favours the lower end of the range to limit cumulative irritation
Relevant Standards
- OECD Test Guidelines (use oral gavage as a dosing route for acute and repeated-dose oral toxicity studies)
- Good practice guidance on the administration of substances to laboratory animals (Diehl et al., 2001; Turner et al., 2011)
- Institutional animal ethics committee approval (AEC in Australia; IACUC in North America) is the authoritative source for approved volumes
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Frequently Asked Questions
What is the maximum oral gavage volume for a mouse?
The widely used good-practice volume for a single oral gavage in mice is 10 mL/kg body weight. For a typical 20 g mouse this is 0.20 mL (200 microlitres), and for a 30 g mouse it is 0.30 mL. Some published guidance permits more with explicit justification, but 10 mL/kg is the figure most institutions work to. Lower volumes are preferred where the dose formulation can be concentrated, and the volume approved by your institutional animal ethics committee is the authoritative limit.
What is the maximum oral gavage volume for a rat?
For rats, 10 mL/kg body weight is the widely used good-practice volume for a single administration, so a 250 g rat receives about 2.5 mL. Turner et al. (2011) give a wider range of 10 to 20 mL/kg for rats, but volumes above 10 mL/kg should only be used where the institutional protocol explicitly approves them. Chronic or repeat dosing studies generally work at the lower end of the range.
How do I calculate the gavage volume for a given animal?
Multiply the animal's body weight in kilograms by the volume rate in mL/kg. At 10 mL/kg, a 0.025 kg (25 g) mouse receives 0.025 x 10 = 0.25 mL, and a 0.25 kg (250 g) rat receives 0.25 x 10 = 2.5 mL. Weigh each animal before dosing and calculate its volume individually, since body weight varies across a cohort.
Why does gavage volume matter?
The stomach has a limited capacity, and delivering too large a volume can cause gastric distension, reflux into the oesophagus, altered gastric emptying, and a measurable stress response, any of which may confound study results or harm the animal. Keeping to the 10 mL/kg good-practice volume, and using the smallest practical volume, protects both animal welfare and data quality.