Researchers in both the U.S. and England conducted the earliest vitamin research on rats in the early 1900's. Rats are popular today in other types of research, such as psychological and biological tests, because they're easy to use. Their light food consumption makes them economical in the lab. It is possible to evaluate the effects of minute amounts of experimental material on rats -- a test that is impractical with larger animals.

Physiologically, rats are similar to other single-stomached animals, except for their lack of a gall bladder and their diffuse pancreas, an organ that is well-formed in other monogastric animals. Three bile ducts lead directly from the liver to the duodenum. The best research results are obtained from uniformly sized rats that are produced in closed colonies. By using rats from the same source you can ensure uniformity of size, good reproduction, and fewer genetic variations.

Frequent handling of the animals will make them gentle and easier to control. Handling will permit you to check them for physical defects and the presence of external parasites. A gentle, firm grip around the thoracic cavity is comfortable for the rat, while still restricting movement. Young rats usually have to become accustomed to handling gradually because they are so playful and active.

Psychological tests have proved that rats are highly intelligent and sensitive. They need attention and will usually come to the front of their cages when a human being approaches. Rats will stay cooperative and easily manageable if they are treated kindly and if their cage area is kept clean and quiet.

Strains of inbred mice are a special category of animals for research uses. Usually inbred mice have higher mortality and poorer growth rates than outbred mice. They are subject to cannibalism, uneven temperaments, and some birth defects. But these mice do serve important functions. Breeders, for example, have developed inbred strains of mice that are susceptible to muscular dystrophy, a debilitating human disease whose cure is still unknown. Various strains are bred to have other inborn errors of metabolism that aid the biologist in gaining an in-depth knowledge of abnormal reactions.
On arrival at the laboratory, new mouse shipments should be placed in quarantine and the shipping material should be burned. It is best, if possible, to avoid mixing animals that come from different suppliers.

Gentle handling of the mouse is important because it affects its disposition. Gloves or forceps should never be used to pick up a mouse. It's easier to catch the active mouse if you use your hand as a dipper and hold the mouse's body gently in the palm of your hand, letting the head stick out between your thumb and forefinger.

Individual mice are hard to differentiate in a group. The ear punch method of marking is a practical way to identify up to 100 mice. If more than 100 are in a colony, toe clipping and fur dyeing can be used as alternative methods.

Three types of hamsters are commonly used in laboratory research: the Golden hamster, the European hamster, and the Chinese hamster.

The Golden hamster, also known as the Syrian Golden hamster, is the most popular in U.S. laboratories. It is also used frequently in many other countries. This breed's name may be misleading, since its color may range from albino to dark brown with a light gray belly. The Golden hamster has twice as many chromosomes as the other breeds, with 44. It has a friendly, gentle disposition and it more easily adapts to captivity than the European or Chinese hamsters, making it preferred among breeders and researchers.

The European hamster is also known as a black-bellied hamster for a good reason; it has a black belly and brown back. This strain is rarely used outside of Europe.

The Chinese hamster is used frequently in Asia for laboratory research. It has striped sides, thus is sometimes referred to as a striped hamster.

The hamster is prolific, easy to handle and able to resist infection, useful qualities in a research environment. Hamsters are docile animals if they are treated kindly and given a comfortable cage. During the day they often sleep, but at night they are very active and require room in which to exercise. They enjoy playing on exercise wheels.

Anatomically, the hamster is more like the rat than any other member of the rodent family. Its large cheek pouches and short stubby tail clearly distinguish it from other lab rodents. The pouches are valuable to researchers interested in studying circulation because part of the circulatory system is very near the surface in this area.

The laboratory uses of the hamster are similar to those of other rodents, but they are used less often because their reactions to tests are not yet well known. The hamster has been shown to have a more specific reaction to certain experiments, such as those involving growth of cancerous tumors. Besides cancer research, hamsters are used in diabetes and radiation research and in vascular physiology studies.