Enzyme immunoassay for on-line sensing of milk progesterone

Reproductive management is a major financial concern for the dairy industry, with inefficient estrus detection as the foremost cause of lost income. The most accurate predictors of estrus are baseline patterns of reproductive hormones such as progesterone. To quantify progesterone concentration, blood samples are assayed in vitro using enzyme immunoassays (EIA). These assays generally require several hours to perform. Progesterone concentrations in milk are similar to those in blood plasma and, thus, provide a convenient means for on-line estrus detection. We have modified a standard progesterone EIA for use with a biosensor to measure hormone concentrations each time a cow is milked. The kinetics of the antibody-antigen reaction were studied. We have shown that a total assay time of 4 min (2-min antibody-antigen binding, 2-min substrate development) is sufficient for monitoring progesterone concentrations. Further work is needed to improve the sensitivity of the measurement protocol.