Abstract: This study aimed to provide important reference for the development of silent estrus identification technology based on the fact that male and female cows communicate through sex pheromone. The 25 healthy Holstein cows aged 3 to 5 weeks from Shijiazhuang Tianquan Good Breed Dairy Co. Ltd. were pre-selected, which were 15 to 35 d postpartum, and artificial observation, activity monitoring, rectal examination and B-ultrasound detection and other methods were used to identify the estrus of Holstein cows, and distinguish between normal estrus and silent estrus. The saliva samples of a total of 4 normal estrus and 5 silent estrus cows were collected at different stages of estrus. The Solid Phase Micro-extraction Gas Chromatography-Mass Spectrometry (SPME-GC-MS) was used to identify and analyze the volatile compounds in these saliva samples, and compare the differences between different estrus states and different estrus stages. The results showed that 40 compounds were found in the saliva of all cows, and 23 compounds with significantly higher content during estrus than before estrus (P<0.05) were screened out by paired analysis, among which 13 compounds (1-Pentanol, pyrrole, 1-Hexanol, 3-hexen-1-ol, Phenethyl alcohol, 6-methyl-2-heptanone, 6- (2,2,2-trichloro-1-hydroxyethyl)-1-methyl Cyclohexene and 2-pentylfuran, 2-methyl-1- pentanol,2,6,6-trimethyl-2-neneneba cyclohexene 1,4-dione, 3-methyl-1-butanol, Methylsulfonylmethane, Sulfonyl group bismethane) showed an increasing trend in all cows during estrus. These compounds can be used as estrus candidate markers for cow estrus identification, and their content is small in difference between normal estrus and silent estrus cows, providing important reference for simultaneous identification of normal estrus and silent estrus.

Key words: Holstein cow, estrus identification, saliva, pheromones