Abstract
Corticosterone and cortisol have been positively identified in jugular vein plasma in dairy cattle under normal dairy environment. The corticosteroids were extracted from plasma with dichloromethane and purified by solvent partition and paper chromatography. Quantitative analysis was carried out by isotope dilution and spectrophotometry. Criteria for identification Included solvent partition, Chromatographic mobility on paper and thin-layer, ultraviolet, sulfuric acid and infrared spectrum analysis. Other criteria included a maintenance of constant specific activity after chromatography of the free steroids and the steroid acetates each in three different chromatography systems, and non-separation of the steroid from internal radioactive standards throughout the solvent and Chromatographic partitions. The levels found in plasma from 18 lactating, non-pregnant dairy cows varied from 1.5 to 5.1 μg (mean = 3.0 μpg) corticosterone and 3.2 to 13.1 μg (mean 7.2 μg) cortisol per 100 ml. The ratio of cortisol/cortico-sterone varied from 0.85 to 5.94 with a mean of 2.40 for these dairy cows.
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