The role of pheromones and biostimulation in animal reproduction

It is now known that pheromonal communication plays an important role in ma mmalian behaviour and reproductive processes. Chemical communication with p heromones is one means of transmitting such information. In mammals, signal ling and priming pheromones are thought to act either singly or in combinat ion through olfaction, auditory, visual (sight) or tactile stimuli. Pheromo nes are air-borne chemical substances ("signals") released in the urine or feces of animals or secreted from cutaneous glands that are perceived by th e olfactory system and that elicit both behavioural and endocrine responses in conspecifics. Extensive studies in insects, rodents, swine, sheep, goats and cattle have established the importance of pheromones in the strong influence exerted by the male on reproductive activity in the female. There is a pheromone prod uced by the queen honey bee, which has two functions: inhibition of queen r earing and suppression of oogenesis in workers and in addition attracts dro nes during nuptial flight. It has also been demonstrated that the urine of male mice, rats, feral species and other wild rodents contains a priming ph eromone that is responsible for hastening puberty in the females. Pheromone s in the wool, wax and urine of a ram are sufficient to stimulate ewes to o vulate, while the buck has a strong characteristic seasonal odor and a buck jar containing the odor of the buck can be used as an aid in the detection of oestrus in does. The mere presence of the boar at the time of inseminat ion of the sow improves sperm transport and ovulation, while the presence o f the vasectomised bull has been reported to hasten the onset of puberty in heifers and also early resumption of ovarian activity in cattle following parturition. The role of pheromones in bovine reproduction is not as clearl y defined as in sheep, goats and swine. Pheromones and other allelomimetic cues can exert profound effects on repro ductive activity via the hypothalamic system that generates pulses of gonad otropin-releasing hormone. Manipulations of these factors and other pathway s linking environmental inputs to reproductive output can lead to developin g the concept of "control systems technologies", aimed at controlling repro ductive performance. The knowledge acquired on the effectiveness of biostim ulation: the factor which conditions it and the biological mechanism which produces it in livestock species, allows its use as a breeding management t ool. The understanding of the role of pheromones could be of potential econ omic importance in addressing some of the problems associated with livestoc k production in the tropics. The biostimulation technique offers a potentia lly useful and practical way to improve reproductive efficiency in livestoc k species in the tropics. The exact nature of the cues and the role of bios timulation in livestock species especially swine, sheep, goats and cattle i n developing countries require more attention. (C) 2001 Published by Elsevi er Science B.V.