Estimation of melatonin in bovine plasma: patterns in Jersey heifers treated with cloprostenol at two times of day.

The estimation of melatonin in bovine plasma by radioimmunoassay is described and some aspects of specificity are discussed. Mean values for individual heifers ranged from 0.025 to 0.25 nmol/l during the day and were significantly (P less than 0.01) raised in each animal to mean values of 0.19 to 1.41 nmol/l at night. The hormonal changes after cloprostenol injections were not affected by the time of day at which the heifers were treated.