How long does it take for a rat to grow? - briefly
Rats achieve sexual maturity at about five to six weeks and reach full adult size by eight to twelve weeks. After the third month growth slows considerably, with weight stabilizing around 300–500 g for typical laboratory strains.
How long does it take for a rat to grow? - in detail
Rats reach full physical size within a defined developmental schedule that varies among species, strains, and environmental conditions. The process can be divided into distinct phases.
The prenatal period lasts approximately 21–23 days, during which embryonic development proceeds rapidly. After birth, neonates are hairless, blind, and weigh about 5–7 grams. The first two weeks constitute the lactation stage; pups double their birth weight and begin to open their eyes around day 14.
Weaning occurs between days 21 and 28. At this point, offspring transition to solid food, and growth rate accelerates. By the end of the third week, body mass typically reaches 30–40 grams, representing roughly 50 % of adult weight.
Sexual maturity is achieved between weeks 5 and 7 for most laboratory strains. Males exhibit testicular development, while females enter estrous cycles. Physical dimensions approach adult proportions, though slight increases in body mass continue.
Full adult size is generally attained by week 10 to 12. Standard laboratory rats (e.g., «Rattus norvegicus») average 250–300 grams, with a length of 20–25 cm excluding the tail. Growth beyond this point is minimal, except in cases of obesity or prolonged high‑calorie diets.
Factors influencing the timeline include:
- Genetic strain (e.g., Sprague‑Dawley vs. Wistar)
- Nutritional quality and quantity
- Ambient temperature and housing density
- Health status and presence of disease
In summary, a rat progresses from birth to mature adult within roughly three months under optimal laboratory conditions, with the most rapid growth occurring during the first four weeks post‑natally.