VOLATILE COMPOUNDS OF BOVINE-MILK AS RELATED TO THE STAGE OF THE ESTROUS-CYCLE

Previous reports on behavioral assays with trained dogs suggested that milk samples from cows at diestrus, proestrus, and estrus had differe nt odors. To identify the odor differences, volatile compounds in milk were isolated and analyzed by gas chromatography and mass spectrometr y. About 80 peaks were detected in each chromatogram, of which 59 were present in all samples, and 23 were tentatively identified. The major identified compounds included the following six structurally distinct classes: ester, aldehyde, ketone, alcohol, fatty acid, and lactone. A lthough no unique peaks were found to be specific to samples taken at diestrus, proestrus, or estrus, 36 compounds exhibited significant dif ferences in concentration among the three reproductive stages. These q uantitative differences may account for the variation of milk odors du ring the estrous cycle. In order to investigate the quantitative diffe rences systematically, multivariate discriminant techniques were used to relate the gas chromatographic profiles with the three stages of th e estrous cycle. Stepwise discriminant analysis indicated that 15 of t he 59 peaks in each chromatogram could best be used to reveal the diff erences among milk samples taken at diestrus, proestrus, and estrus st ages. The discriminant function based on the 15 key peaks could classi fy all of the samples into their original categories at a total accura cy of 97.9%. Canonical analysis indicated that milk samples from diffe rent stages were clearly separated from each other in a two-dimensiona l space.