Abstract
Summary
The concentration of progesterone in milk and blood plasma was determined by radioimmunoassay in 56 pregnant cows. Samples were from eight cows on each of the following days of pregnancy: 30, 60, 90, 120, 150, 180, and 210. Validity of the assay was indicated by parallelism among unknowns, whether milk or plasma, and between unknowns and the standard. Progesterone was higher (P < 0.005) in milk (21.2 ng/ml) than in blood plasma (5.3 ng/ml) averaged over all days of pregnancy. The difference among days and the interaction of day and type of fluid (milk vs plasma) were not significant.
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