How much should a female rat weigh? - briefly
Adult female rats usually weigh between 150 g and 250 g, with the exact figure depending on strain, age, and nutritional status. Juvenile females are lighter, often ranging from 80 g to 120 g.
How much should a female rat weigh? - in detail
The normal body mass of an adult female laboratory mouse‑rat hybrid falls within a narrow range that reflects species, strain, and age. For a standard laboratory strain such as Sprague‑Dawley, mature females typically weigh between 200 g and 250 g. In other common strains, the limits shift slightly:
- Wistar: 180 g – 230 g
- Long‑Evans: 190 g – 240 g
- Fischer 344: 170 g – 210 g
Juvenile females exhibit progressive weight gain until reaching these adult values. A 4‑week‑old pup usually measures 45 g – 55 g; by 8 weeks the weight approaches 150 g, and by 12 weeks it stabilizes near the adult range.
Factors influencing body weight include:
- Nutrition: ad libitum access to a balanced rodent diet maintains target mass; caloric restriction reduces weight proportionally.
- Reproductive status: pregnant or lactating females gain 30 g – 50 g above baseline, with a rapid return to normal after weaning.
- Health condition: illness, parasites, or chronic stress can cause weight loss of 10 % or more, signaling the need for veterinary assessment.
- Environmental temperature: ambient temperatures below 20 °C increase metabolic demand, potentially lowering weight if food intake does not compensate.
Accurate monitoring requires weekly weighing with a calibrated scale, recording the data in a log to detect trends. Deviations exceeding ±5 % of the expected range merit investigation of diet, housing, and health status. Maintaining females within the specified weight interval supports optimal physiological function and reliable experimental outcomes.