How much should a four‑month‑old rat weigh? - briefly
A rat aged four months typically weighs 200–300 g. Males usually reach the upper end of this range, while females are nearer the lower end.
How much should a four‑month‑old rat weigh? - in detail
A rat that is four months old is nearing adult size. Expected body mass depends on strain, sex, nutrition, and health status.
Typical weight ranges for common laboratory and pet strains are:
- Sprague‑Dawley male: 300 – 350 g
- Sprague‑Dawley female: 250 – 300 g
- Wistar male: 280 – 340 g
- Wistar female: 230 – 290 g
- Domestic pet male: 300 – 500 g
- Domestic pet female: 250 – 400 g
These figures represent 80 %–90 % of the strain’s mature weight. Males consistently exceed females by 10 %–20 %. Adequate protein (18 %–20 % of diet) and caloric intake (15–20 kcal / 100 g body weight) support growth; deficiencies delay weight gain. Illness, parasitism, or chronic stress can reduce body mass by 5 %–15 % below the expected range.
Growth curves show a rapid increase from birth (≈20 g) to 2 weeks (≈50 g), then a steadier rise to 4 months. After this point, weight plateaus unless significant dietary changes occur. Monitoring weight weekly from weaning provides a reliable indicator of normal development and early detection of health problems.
In practice, record the animal’s weight with a calibrated scale, compare to the appropriate range above, and adjust husbandry if measurements fall outside expected limits.