General biology and management Rats have a highly developed sense of smell and hearing but vision is poor and colour vision is non-existent. They have a well-defined diurnal rhythm, being active during the dark and sleeping and resting during the light hours. Feeding occurs at night and digestion during the early daylight hours. During this period caged rats are easily handled. After repeated gentle handling they can be trained to receive some noxious stimuli such as injections with minimal restraint.
Males are more aggressive than females.
Rats will bite without warning but not repeatedly. Animals of the same sex may be housed together and when a male is placed with a female it will attempt to mate immediately, although the female will accept the male only in early oestrus. A vaginal plug, which is a mixture of secretions of the vesicular and coagulating glands of the male, fills the vagina from the cervix to the vulva after mating. Plugs remain for several hours and then fall out and are usually seen on the bottom of the cage. Observation of a vaginal plug is taken as the first day of pregnancy.