Throughout the lives of most mammalian species, the sense of smell plays an important role in response to chemical messengers that are involved in many different behavioral activities. Pheromones are the most important compounds for olfactory communication. The term pheromone was invented by Karlson & Lüscher in 1959. Pheromones are chemical substances that, when emitted from one animal, cause behavioral or physiological responses in other animals of the same species. Pheromones are secreted by specific organs that are widely scattered on the bodies of different animals. Released pheromones stimulate rapid behavioral changes in the neuroendocrine system and subsequently produce a physiological and behavioral change in the receiving individual. Pheromones also indicate an animal's identity and territory. Pheromones in mammals convey specific information concerning species, gender, physiological phases and identities of animals, thus triggering stereotyped behavioral and neuroendocrine responses. Such responses ensure breeding and hierarchical order in the animal group.
Olfactory communications between conspecific mammals facilitate reproductive processes. Pheromones produced by males and females influence their sexual behavior and hormone activity (Marchlewska-Koj, 1984). In most species, males can distinguish between females in estrus or anestrus phases by their scents. Females, too, are able to identify sexually active males by odor. Production of such olfactory stimulants is controlled by gonadal hormones, mainly testosterone. Pheromones produced by males can accelerate puberty in juvenile females, induce estrus in anestrus females and block pregnancy in recently inseminated females.