Embryonic mortality in dairy cows estimated by nonreturns to service, estrus, and cyclic milk progesterone patterns.

Cyclic patterns of progesterone in milk were studied in 262 Holstein cows. Milk progesterone data were obtained from 153 cows for at least 75 days after conception as indicated by continuous high progesterone concentrations in milk for 28 days or more following artificial insemination. Cycling was reinitiated in 11 of these cows between 28 and 75 days after breeding, for an estimated 7.2% rate of embryo-fetal mortality. This was considerably less than a corresponding rate of 22.7% estimated for this herd by the delayed returns to estrus (28 to 75 days). In 350,180 cows inseminated with semen from Holstein bulls the estimated embryo-fetal mortality by the same delayed return to service method was 12.5%. Biases in this latter method of estimation are discussed.