When does a rat develop fur? - briefly
Rats are born without fur; hair begins to emerge at about five to seven days old and is usually complete by two weeks.
When does a rat develop fur? - in detail
Rats are born hairless, with a thin layer of soft, down‑like lanugo covering the body. This initial covering appears during the late embryonic stage, typically around day 18 of gestation, but it is shed shortly after birth.
The first true fur emerges during the first post‑natal week. Between days 4 and 7, the dorsal and ventral surfaces begin to develop coarse guard hairs, while the surrounding regions acquire finer underfur. By the end of the second week (day 14), most of the body is covered with a complete pelage, although the tail may remain relatively sparsely furred until day 21.
Key developmental milestones:
- Embryonic lanugo: appears ~day 18 of gestation, provides minimal insulation.
- Hair follicle activation: occurs immediately after birth, initiating keratinocyte proliferation.
- Guard hair formation: starts ~day 4, visible as coarse hairs on the back and sides.
- Underfur development: follows guard hairs, filling gaps and providing thermal regulation.
- Complete coat: generally achieved by day 14; tail fur may finalize by day 21.
Factors influencing the rate of pelage maturation include genetic strain, ambient temperature, and maternal nutrition. Laboratory strains such as Sprague‑Dawley typically follow the timeline described, while wild‑derived rats may exhibit slight variations, often reaching full coat slightly earlier due to environmental pressures.
Understanding these stages assists in scheduling experimental procedures that depend on thermoregulation, as the presence of a full coat markedly improves the pup’s ability to maintain body temperature.