A healthy rat

The laboratory rat is the domesticated form of the species Rattus Norvegicus. This species lives in shallow tunnels and burrows (see movie 1), usually in the vicinity of water. The animal tends to avoid open spaces. There are currently more than 400 outbred and inbred strains, each with its own specific selection of the genetic variation of the wild rat. A healthy laboratory rat is alert, curious, engages in social interactions (see pictures and movie 2), looks well-nourished and clean, and is vivacious. The extent to which a rat can satisfy species-specific behavioural needs, determines in no small measure its state of well-beingWell-being A complex and dynamic internal state that includes: successful biologic functioning, positive experiences, and absence of negative conditions. The animal adapts effectively to internal needs and external stimuli and maintains a good mental state.. Knowledge of wild rat behaviour is an important frame of reference for evaluating the behavioural repertoire of laboratory rats.

Rats have a short lifespan with an associated high metabolic rate and rapid maturation and reproduction. In general they have large litters.

Activity

The rat is a nocturnal animal. The rat engages in exploratory behaviour for orientation in its environment (food, threats). Rats prefer to eat when it is dark and they are in their most active phase. They are gnawers and will chew on and damage materials such as wood and plastic.

Rats are social animals. Single housing can lead to boredom and potentially result in stereotypic behaviourStereotypic behaviour A phenomenon that appears as a response to chronic stress. It is manifested as a set repeated pattern of seemingly purposeless activity.. When animals are fed ad libitumAd libitum Latin. At one's pleasure, free. In laboratory animals context: unlimited supply of food. Antonym: Restricted., they can easily become overweight.

The rat spends about 40% of its time on coat and body groomingGrooming The behavior animals engage in to keep clean. Grooming removes dirt from fur and body openings. Absence of this behavior indicates reduced well-being., usually after eating, drinking, or exploring. Decreased grooming quickly becomes apparent and can be seen around the anus, and in the form of a reddish-brown secretionSecretion The production of fluids by glandular organs or tissues in the body. around the eye and sometimes the nose, produced by the Harder gland and known as ‘red tearsRed tears Dried reddish-brown secretions of the Harderian gland (porphyrins). An increased production or decreased removal of porphyrin is indicative of reduced well-being and can frequently be observed in stressed rats. It may also be a sign of less meticulous grooming.’ (see picture).

An unkempt coat and the presence of ´red tears´ are frequent early signs of health problems. An unkempt coat is normal in older animals.