Fertility control in cattle by use of the "milk progesterone test"

The development and validation of a radioimmunoassay for progesterone in cow's milk is described. Control of the temperature during storage of the milk and also during the sample incubation procedure appeared to be a critical requirement with respect to reduction of nonspecific binding of tritiated progesterone. Ranges of milk progesterone levels were established during pregnancy as well as during the luteal and the follicular phase of the oestrus and of pregnancy in three trials on two experimental farms. The mean accuracy with respect to the diagnosis "pregnant", "non-pregnant" or "not in oestrus" were 84.0, 97.6, and 100%, respectively. By leaving out of account all animals with high progesterone values (greater than 10 ng. ml(-1)) on day 1 (= day of insemination) the accuracy of the diagnosis "pregnant" was improved to 87.1%.