Volatile fatty acids are the main energy product from rumen fermentation. This study investigated the individuality of VFA concentrations in samples of rumen fluid obtained from 10 Holstein cows using a esophageal probe to take samples repeatedly over a 7 week period. Systematic changes were seen for propionic acid after onset of lactation, but acetic and butyric acid was not affect. Repeatability was generally low, but highest for propionic acid. VFA traits should be used as supplementary information in metagenomic studies