Abstract: To investigate the interindividual variation of plasma proteome of dairy cows and evaluate the minimal size of samples for proteomic analysis. In this study, plasma samples in early lactation dairy cows were collected and the proteome profiles of these samples were analyzed using two-dimensional gel electrophoresis. After visualization proteins with Coomassie Blue G-250 solution, the coefficient of variation values of 56 protein spots were analyzed and ranged from 8.7% to 59.6%. The five proteins with coefficient of variation values ranged from 35% to 59.6% were identified by ion trap mass spectrometer, and three spots identified as transthyretin, apolipoprotein A1 and alpha 1 acid glycoprotein. Moreover, the one-way ANOVA feature showed a correlation between sample size and individual variations. The results showed that when the sample size exceeded 4, the individual variations were not significant to the whole pool. The results indicated that individual variations are encountered in plasma protein expression profiles and further for number of samples (sample size) needed to detect given protein expression differences with statistical significance.

Key words: dairy cows; plasma; proteome; individual variations