How much do male rats weigh? - briefly
«Adult male rats generally range from 300 g to 500 g, with common laboratory strains such as Sprague‑Dawley averaging 350–400 g». «Weight varies with age, diet, and genetic background».
How much do male rats weigh? - in detail
Male rats of laboratory strains typically reach an adult body mass between 300 g and 500 g, although considerable variation exists among genetics and husbandry conditions. The lower end of the range corresponds to smaller strains such as Long‑Evans, while larger strains like Sprague‑Dawley often approach the upper limit.
Factors that modify weight include genetic background, age, nutritional regimen, ambient temperature, and cage density. Younger animals display rapid growth; weight gains of 20–30 g per week are common during the first six weeks after weaning. After this period, growth slows, and adult weight stabilises by eight to ten weeks of age.
Typical adult weights for frequently used strains are:
- Sprague‑Dawley: 350 g – 500 g
- Wistar: 300 g – 450 g
- Long‑Evans: 250 g – 350 g
- Fischer 344: 200 g – 300 g
These values represent averages from multiple breeding colonies; individual specimens may fall outside the reported intervals.
Accurate mass determination requires calibrated analytical balances with a precision of at least 0.01 g. Animals are usually weighed in a metabolic cage or on a platform while restrained gently to minimise stress‑induced weight fluctuations. Repeated measurements at consistent times of day reduce variability caused by feeding cycles.
In experimental protocols, body mass influences drug dosage calculations, metabolic rate assessments, and cage‑space planning. Ensuring that each male rat conforms to the expected weight range supports reproducibility and ethical standards in biomedical research.