Health and activity

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 over 400 outbred and inbred strains, all derived from the wild rat via a specific selection pathway. 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-being. 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. 


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 they will chew at and destroy materials like wood and plastic.

Rats are social animals. Single housing can lead to boredom and potentially result in stereotypic behaviour. When animals are fed ad libitum, they can easily become overweight.

About 40% of a rat's time is spent keeping coat and body clean, usually after feeding, drinking or exploring. Decreased grooming quickly becomes apparent and can be seen around the anus, and in the form of a reddish-brown secretion around the eye and sometimes the nose, produced by the Harder gland and known as 'red tears' (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.

Movie 1: subterranean habitat of the rat.

Three healthy rats in a cage. The animals are alert, active and have a flat coat, are well-groomed and have faeces of normal consistency.

Movie 2: social behaviour of the rat.

Exploratory behaviour of the rat.

Two rats with diarrhea. The animal in front has a dirty coat, is not well-groomed and has lost weight (sunken flanks). In the left side of the cage a large bolus of soft stool can be seen.   

"Red tears"