Aggression in fancy rats

Aggression in fancy rats is not a pleasant theme. Nobody likes to think that their wonderful baby rat with the soft fur can become a monster with teeth and claws. At the same time aggression is one of the two traits that serious Norwegian breeders are most concerned about. They wish to breed aggression out, (and breed health in). This just shows how lucky we are to have rats for pets! Rats are among the most studied animals for aggression. There are hundreds of scientific articles, and some are even available for free on the Internet. There are good articles written for the layman too, about rat aggression. Unfortunately the popularized articles did not answer all my questions. That is why I started gathering information from original sources. Many of the answers I was looking for do not exist yet. Even so I found exciting news that made me sit up straight and take notes.
If you would like to read about current knowledge of rat aggression, about different types of aggression, I hope you will find something worthwhile here. The references are so numerous I have put them on a separate webpage.

Aggression and inheritance

Imagine taking a gene test to learn if your rat was carrying inheritable aggression! What a difference it would make for breeding! Alas, that gene test does not exist. In spite of all the rat research there are still so much we do not know yet. Among mice and men, gene mutations have been found which cause aggressive tendencies. With mice there are even models for creating these gene mutations in the laboratory. The rats, however, have not been as complacent. Even so it is quite evident that some gene mutations can lead to aggression in rats. Actually, we know that different gene mutations can lead to different kinds of aggressive behaviour. For that reason any hope of taking just one gene test must be rudely crushed from the start. One blood sample might do, but there would have to be a whole array of tests performed.

One rat can live harmonically with its kin, but attack humans again and again. Another rat is the perfect, lovable pet in the arms of its owner, but is turned into a killing machine when presented with baby rats. Some does are only aggressive when pregnant or while nursing. Some rats get along well in their own group but go bananas over strangers. There are rats that mainly show aggression in a feeding situation, or in a particularly stressful situation. Other rats are selectively aggressive against their own or the opposite sex. Then there are those who will pick on a particular victim, and those that simply cannot stand any other rats. It is possible that some of these forms of aggression have the same genetic cause. Some are unquestionably unrelated. Aggression, however, is not always (or perhaps even as a rule) inherited. Environmental factors will be discussed further on. This chapter focuses on current knowledge of inheritable aggression in rats.

As we do not know the genes that cause aggression in rats, we cannot study the effects of gene manipulation directly. Evidence for inheritance comes from two types of trials. One is breeding for low and high aggression. The other type of evidence comes from comparing existing lines of laboratory rats. The results can hardly have come as a surprise to the scientist. People experienced in laboratory animals do not need a controlled study to discover that with regard to aggression, Sprague-Dawly rats are different form Fischer-rats... For the benefit of less experienced rat handlers the difference has now been documented. There is also evidence that the tendency to bite when subject to pain is independently inheritable from the tendency to bite when restrained. Restrain aggression have no direct link with aggression when competing for food. And aggressive behaviour because of social isolation can be inherited independently of all the three above.