How much does a one‑year‑old rat weigh? - briefly
A one‑year‑old laboratory rat generally weighs between 250 g and 300 g, with variations due to strain, sex, and nutrition.
How much does a one‑year‑old rat weigh? - in detail
A twelve‑month‑old laboratory rat typically weighs between 250 g and 350 g. The exact mass depends on strain, sex, and husbandry conditions.
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Strain differences:
• Sprague‑Dawley: 260‑320 g
• Wistar: 250‑300 g
• Long‑Evans: 280‑340 g -
Sexual dimorphism: Males exceed females by roughly 10‑15 % in the same strain.
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Dietary impact: Standard chow yields the weights listed above; high‑calorie formulas can increase body mass by 20‑30 % without altering growth rate.
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Housing factors: Group housing may reduce individual weight by 5‑10 % compared to isolated cages, owing to competition for food and reduced stress.
Growth follows a sigmoidal curve: rapid gain in the first six weeks, a plateau from weeks eight to twelve, then a gradual increase until adulthood. By the end of the first year, skeletal development stabilizes, and further weight changes reflect fat accumulation rather than lean tissue growth.
Weight measurement should use calibrated electronic balances with a precision of ±0.1 g. Animals are weighed in the morning after a brief fasting period to minimize gastrointestinal content variation.
In summary, a rat at twelve months typically falls within the 250‑350 g range, with precise values determined by genetic background, sex, nutrition, and environmental conditions.