This article is from the Mar./Apr. 1986 AFRMA Rat & Mouse Tales news-magazine.

By Ivan Golakoff, Administrative Assistant & Educational Director,
Animal Care and Education Center, Rancho Santa Fe, CA

Pheromones are a type of triggering chemical secreted by many mammals which alter or affect a recipient animal’s hormonal state. They often trigger behavioral actions in surrounding animals and have a strong implication in controlling sexual behavior in mammals.

Studies done by Parkes and Bruce in 1961 and Bronson in 1971, show the strong affect hormones have on the estrus cycle of female mice. Tests done on Mus musculus or laboratory mice show that when mice are kept in large groups, some individuals become anestrus.

When kept in small groups, some mice developed pseudo pregnancies through continued secretions of the corpus luteum in the absence of fertilization.

The anestrus condition can also be induced by removing the female’s olfactory bulbs.

It has been found that adding one or more males to a group of females will produce a regular and shorter estrus cycle.

Marsden and Bronson (1964) also showed that when male urine was added to the female nares, it produced the same effect. Whitten, Bronson, and Greenstein (1968) also showed that female mice caged downwind from male mice, developed synchronized estrus cycling. Females that were caged upwind in fact tended to not show any such signs and some even became anestrus.

Another affect of pheromones on mice can be noticed in the physiology of reproduction. Tests show that a pregnancy can be blocked if a newly impregnated female is exposed to a male other then her mate. Estrus will usually resume within a week. This same effect can be seen by just exposing the female to the urine of the alien male.

As can be seen, pheromones can be a powerful stimulus for behavior and must be considered when breeding mice.

Reference: Smith. The Behavior of Communicating. Harvard Press, 1977. (An excellent book)