Flehmen response in bull: role of vaginal mucus and other body fluids of bovine with special reference to estrus

Abstract

The present investigation was carried out with a view to evaluate the frequency of Flehmen behaviour in bull in response to body fluids of cows in various stages of the estrous cycle, in the context of estrus detection. The study was performed on free moving bulls under natural conditions. Samples of vaginal mucus, saliva, faeces and milk of pro-estrus, estrus and di-estrus stages collected from donor cows were rubbed individually onto the genital regions of non-estrus animals (dummy cows) and the bulls were observed for 30 min for assessment of Flehmen behaviour. The duration of Flehmen behaviour shown by bulls was maximum towards the dummy cows receiving estrus sample. Such Flehmen behaviour, however, did not occur in bulls in response to the cows receiving samples of other stages. The statistical significance was higher (P<0.001) in exhibiting repeated Flehmen behaviour towards estrus as compared to those of pro-estrus and di-estrus. Among the various body fluids tested, the exhibition of Flehmen behaviour was significantly higher (P<0.01) in response to estrus vaginal fluid. No response was observed on dummy cows (control) to which only water was applied on the genital region. The results suggest that vaginal mucus may act as an additional/secondary source along with urine in eliciting copulatary behaviour and executing coitus in bulls during estrus. The results further suggest that in addition to vaginal mucus, other body fluids like saliva, faeces and milk have estrus-related odours and are probably involved in bovine bio-communication.

Introduction

Chemical communication plays an important role in mammalian sexual behaviour and reproductive processes (Halpin, 1986, Dominic, 1991, Rekwot et al., 2001, Archunan, 2003). It is well documented that the female produces a specific odour during estrus through vaginal discharge and urine which constitutes a major source for mammalian chemical communication. Widespread distribution of estrus-related odours in other body fluids of some mammalian species, more specifically, the cow have been reported (Kiddy et al., 1984). For instance, sexually experienced males preferred the saliva of estrus females to that of non-estrus females in Mongolian gerbils (Block et al., 1981). It has been shown that the concentration of volatile compounds in the faeces differed based on sex and stage of the reproductive cycle and had a characteristic chemical finger print (Kimura, 2001). The volatile compound, γ-12:2 lactone, identified in cow’s milk was shown to be an active odorant (Bendall, 2001) and the lower rumen pH of cows fed on a concentrate diet might facilitate the production of such lactones (Urbach and Stark, 1978).

Estrus-specific bovine urinary chemical cues (pheromones) are identified successfully in our laboratory by gas chromatography linked with mass spectrometry (Ramesh Kumar et al., 2000). Even though urine is the primary source for chemical communication, vaginal fluid is also reported to act as a chemical signal (Klemm et al., 1987). It is possible that urine and vaginal fluid may act together for completion of the pre-copulatary behaviour and successful matting.

The Flehmen behaviour shown by males is an integral part of the premating scenario in mammals (Estes, 1972, Rasmussen, 1998). It is well known that the bull exhibits the Flehmen behaviour repeatedly after inhaling the olfactory cues from cows in estrus (Hradecky et al., 1983, Dehnhard et al., 1991, Ramesh Kumar and Archunan, 2002) sheep (Blissitt et al., 1990, Blissitt et al., 1994), cotton-top tamarins (Ziegler et al., 1993), equines (Ma and Klemm, 1997) and elephants (Rasmussen et al., 1997). Our recent study suggests that the occurrence of repeated Flehmen behaviour is significantly higher in male buffaloes in response to estrus than those of other reproductive stages and establishes that the Flehmen helps in the detection of estrus and provides necessary initiation for successful matting (Rajanarayanan and Archunan, 2004).

The vomeronasal organ (VNO), a peripheral receptor of accessory olfactory system, is very much involved in the perception of chemical communication for mammalian reproduction. The VNO has a direct sub-neocortical projection to the hypothalamic areas that mediates specific behavioural and hormonal responses to chemical (pheromonal) stimuli (Meredith, 1998). The integration and transmission of this information, however, can be modulated by learning mechanisms (Brennan, 2001). It has been demonstrated that the olfactory chemical signals produced from estrus females are mediated through VNO facilitating the matting behaviour through expression of Flehmen response in many species (Halpern, 1987, Johnston, 1998).

There are several reports regarding bio-communication involving bovine vaginal fluid and urine. Investigation on other body fluids, such as saliva, faeces and milk for their biological significance in relation to estrus detection, however, are scanty. Nevertheless, an inexpensive and simple method for improving estrus detection through other body fluids is still strongly needed (Jezierski, 1992). Therefore, the present investigation was carried out (1) to examine whether chemical signals present in bovine vaginal secretion will also be present in other body fluids like saliva, faeces and milk in various stages of the estrus cycle viz., pro-estrus, estrus and di-estrus, determined by bull behaviour and (2) to find out the body fluids which will be more efficient for estrus detection by the response shown by the bull Flehmen behaviour.