Abstract
SUMMARY Samples of whole and fore-milk were obtained from dairy cows on the day of insemination and 24 days later. Whole milk samples only were collected on day 42 after insemination and at the time of rectal examination about two weeks later. The accuracy of pregnancy determination by the assay of progesterone in whole and fore-milk was compared and the effect of correction for fat content of sample was examined. An assessment was made of the relationship between milk progesterone levels at insemination and the conception and calving rates. At the time of insemination, milk progesterone concentration ranges within whole and fore-milk groups were similar for animals having positive or negative rectal pregnancy diagnoses. At day 24, accuracy of pregnancy tests was high in both fore-milk (positive 92·2%, negative 100%) and whole milk (positive 96·7%, negative 100%). Correction of levels to unit fat percentage reduced the difference between whole and fore-milk progesterone levels, but did not improve overall accuracy of pregnancy prediction.
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