Identification of p-cresol as an estrus-specific volatile in buffalo saliva: comparative docking analysis of buffalo OBP and β-lactoglobulin with p-cresol.

Assessment of salivary volatile compounds adopting gas chromatography-linked mass spectrometry (GC-MS) analysis revealed the presence of a total of 11 compounds in the buffalo saliva irrespective of the stages in the reproductive cycle. p-cresol was identified as an estrus-specific volatile compound in the saliva. In addition, modeling of odorant-binding protein (OBP) and β-lactoglobulin revealed that OBP is highly stable and has strong binding affinity with p-cresol. Hydrogen bond interactions indicated that OBP is responsible for pheromone release through saliva. In contrast, β-lactoglobulin, which belongs to the same lipocalin family as OBP, possesses less affinity to p-cresol than OBP, suggesting that it is not involved in p-cresol binding and transport. Phylogenetic characterization revealed that bovine family of OBP is separately clustered. It is suggested that p-cresol has the potential to be developed as a biomarker to detect the reproductive status in the buffalo and for behavioral manipulations.