Short communication: Comparative proteomic analysis of the lactating and nonlactating bovine mammary gland

The objective of this study was to determine how bovine mammary protein profiles vary during lactation and the dry period. Three lactating and 3 nonlactating cows were selected for mammary gland tissue sampling. Compared with the mammary proteins in nonlactating cows, a total of 60 differentially expressed proteins (DEP, including 57 upregulated and 3 downregulated) were identified in lactating cows using 2-dimensional difference gel electrophoresis combined with mass spectrometry. These DEP included enzymes and proteins associated with various macromolecular metabolic processes, and appeared to promote the increased metabolic activity associated with milk synthesis and secretion. The increased DEP were primarily related to initiation, maintenance, and involution of lactation, and included proteins involved in glycolysis/gluconeogenesis, the tricarboxylic acid cycle, the pentose phosphate pathway, oxidative phosphorylation, aminoacyl-transfer RNA biosynthesis, and fatty acid biosynthesis. Identified DEP were further validated by real-time, reverse-transcription PCR and Western blot. Five new DEP associated with lactation were uniquely identified. This work provided some protein-associated insights to facilitate further investigation of the mechanisms underlying lactation in dairy cows.