THERMOREGULATION
Rats have few sweat glands and, being unable to pant, have poor heat tolerance. They do not increase their water intake at high ambient temperatures but instead try to cool down by increasing salivation and seeking shade (Bivin et al.
1979). Death occurs at temperatures over 37° C. The tail and ear are very important for heat dispersion, with blood vessels vasoconstricting and dilating according to ambient temperatures (Fallon 1996; Sharp & LaRegina 1998).Adult brown rats have good tolerance to cold and can adapt extremely well to cold climates by laying down brown fat within 3 or 4 weeks. This can form extensive sheets of pink
The vasodilation of the tail vessels can be used to advantage for venepuncture from the lateral tail vein. The rat should be kept at a warm ambient temperature and the tail immersed in warm water to dilate the blood vessels prior to sampling.
fatty tissue along the ventrolateral and dorsal aspects of the neck (Bivin et al. 1979; Greene 1962). Pups, however, have no intrinsic thermoregulatory mechanisms until the end of the first week of life and are kept warm by siblings and the mother (Fallon 1996; Koolhaas 1999).
The preferred ambient temperature range for captive rats is 18-26° C and with a relative humidity of 40-70%. Unweaned rats that are less than 17 days old and kept at low humidity develop a condition called ringtail. This is where annular lesions on their tail causes the distal end to become necrotic and slough off.
Photoperiod
The rat is mainly nocturnal but will have cycles of activity by day as well as night. A photoperiod of 12 hours day, 12 hours night is recommended for captive rats (Baker 1979; Koolhaas 1999). Albino rats are light sensitive so bright lights should be avoided (Koolhaas 1999).