The chemical profiles of vaginal fluid collected from cows in oestrus and nonoestrus were analysed by gas chromatography-mass spectrometry (GC-MS) to establish any qualitative differences that might have potential value in bovine biocommunication. Eight different organic compounds were detected using the two chromatograms. The chemical profiles of oestrus vaginal fluid were distinguished significantly by the presence of three specific substances, namely, trimethylamine, acetic acid, and propionic acid that were not present in nonoestrus phase. The oestrus specific synthetic compounds were rubbed onto the genital region of nonoestrus animals (dummy cows), and the bulls were allowed to sniff the genital region and observed sexual behaviours. The statistical significance was higher ( ) in bulls exhibiting repeated flehmen and mounting behaviours towards the mixture of acetic acid, propionic acid, and trimethylamine as compared to test these compounds separately. It was concluded that the volatile substances present in the bovine vaginal fluid during oestrus may act as chemical communicators. 1. Introduction The role of pheromones in reproduction has been well documented in several species of mammals [1–4]. The pheromonal cues excreted through faeces, urine, vaginal secretions, saliva, and specialised scent glands play a significant role in sexual and social behaviour [5]. In cattle, it is known that bulls can detect pheromone odours and differentiate between oestrus and nonoestrus urine or vaginal fluid [6–8]. The physical and chemical properties of bovine vaginal mucus have been of long standing interest to reproductive biologists because the mucus enhances conception by facilitating viability and transport of sperm [9]. The oestrus female attracts the male and informs its receptive state by means of chemical signals deriving from vaginal discharge [10] and urine [11]. There is considerable evidence that olfactory components produced from vaginal fluid influence the male sexual behaviour in buffaloes [12], hamsters [13], sheep [14], and bovines [15, 16]. In addition, it has reported that vaginal secretions of heifers at oestrus stimulated sexual activity and mounting behaviour [17]. The individual animal may produce several volatile compounds from a single source but the influence of pheromone activity may be one compound or a mixture of compounds. Hence, it is necessary to analyse the bioactivity of individual volatile compounds identified in the bovine vaginal fluid. However, identification of the volatile compounds in bovine vaginal fluid and knowledge
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