Faecal chemical cues in water buffalo that facilitate estrus detection

Chemo-signals are among the reliable non-invasive methods for estrus detection in mammals. Water buffalo is a silent heat animal and, hence, there is search for chemo-signals which would be effective non-invasive indicators of estrus state. We analyzed the faecal chemical cues during the estrous cycle in buffalo and to find the estrus-specific faecal volatile compounds adopting bull behavior assay. The faecal samples were collected at three phases of the estrous cycle (i.e., proestrus, estrus and postestrus) and subjected to gas chromatography-mass spectrometry analyses. We found 27 volatile compounds in the faeces of buffaloes, of which 4-methyl phenol (4mp) and trans-verbenol (tv) were found only in estrus faeces. The faecal samples of estrus buffaloes and the estrus-specific compound(s) (4mp+tv) at three different concentrations were tested for behavioral responses (flehmen and mounting behavior) in the bull. The bulls exhibited repeated flehmen when exposed to a combination of the two compounds (i.e., 4mp+tv) as compared to the individual compounds or raw faecal sample collected from buffalo when in estrus (P<0.05). However, higher number of mounting behavior was recorded when bulls were exposed to 4mp followed by a combination of the two compounds (4mp+tv) and trans-verbenol (P<0.05), in that order. By contrast, less number of mounting behavior was exhibited by bulls when exposed to the control sample (i.e., Hexadecanoic acid) (P<0.05). As inferred from the bull behavior assay, the present study suggests that the two compounds, 4 methyl phenol and trans-verbenol would be reliable indicators of estrus in buffaloes.