Milk progesterone to predict reproductive status in a commercial dairy herd.

Progesterone was measured in milk strippings of cows to evaluate potential diagnosis of pregnancy and to estimate embryonic mortality. Progesterone in milk was measured at 20 days and at 10-day intervals thereafter through 90 days after artificial insemination when the cows were palpated for pregnancy. Mean progesterone for 24 nonpregnant cows in estrus was 4.5 ng/ml at 20 days after insemination. Cows were classified as pregnant or nonpregnant by a formula which provided a progesterone concentration for which the probability of nonpregnancy was .8. At 20 days after insemination, the success in identifying the nonpregnant and pregnant cows was 87% and 67%. Ten of 34 nonpregnant cows with low (nonpregnant range) progesterone in milk on day 20 were not seen in estrus. Progesterone at sampling intervals after 20 days was used to investigate incorrect assessments. Seventeen nonpregnant cows had progesterone indicative of pregnancy at day 20. Progesterone in milk decreased at various later sampling intervals in all 17 cows. Two of these cows were diagnosed as having pathology of their reproductive tracts. If the other 15 cows experienced death of their embryos, the frequency of embryonic mortality was 28%.