Melatonin levels in Holstein-Friesian dairy cow milk

In the present study, milk melatonin concentrations of 37 Holstein-Friesian cows were determined by ELISA bimonthly for one year to record seasonal melatonin secretion. Mean melatonin concentrations ranged from 5.4 pg/ml in February up to 11.8 pg/ml in August with statistically significantly highest values in August and June and lowest concentrations in February. However, milk melatonin concentration is not related to fat/protein ratio, milk yield, somatic cell score and the number and stage of lactation. Mean melatonin concentration was 9.7 pg/ml prior the dry period, which was statistically significantly higher compared to 6.3 pg/ml after the dry period.