How much does a three-month-old rat weigh? - briefly
A three‑month‑old rat generally weighs between 150 g and 250 g, with variation due to strain and sex. Laboratory strains such as Sprague‑Dawley average approximately 180 g at this age.
How much does a three-month-old rat weigh? - in detail
A three‑month‑old laboratory rat typically weighs between 250 g and 350 g. The exact value depends on strain, sex, and husbandry conditions.
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Strain differences:
• Sprague‑Dawley males average 300 g; females about 260 g.
• Wistar males average 280 g; females about 240 g.
• Long‑Evans males reach 320 g; females near 280 g. -
Sexual dimorphism: Males consistently exceed females by roughly 15‑20 % at this age.
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Nutrition: Standard rodent chow (≈3.5 kcal g⁻¹) supports normal growth; high‑fat diets can increase weight by 10‑20 % within weeks.
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Housing: Group housing may reduce individual weight by 5‑10 % due to competition for food, whereas single housing generally yields higher body mass.
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Measurement protocol: Weigh rats on a calibrated analytical balance to the nearest 0.1 g, preferably after a brief fasting period (2‑4 h) to minimize gut content variation.
Wild‑caught juveniles of the same age show broader variability, often ranging from 150 g to 250 g, reflecting differences in diet and seasonal conditions.
Growth curves for common laboratory strains indicate that the 90‑day mark corresponds to approximately 80‑85 % of adult body mass. Consequently, the weights cited above represent near‑adult size, with further increase of 15‑20 % expected by maturity (≈6 months).