Milk progesterone enzyme immunoassay: modifications and a field trial for pregnancy detection in dairy cows.

A milk progesterone enzyme immunoassay was modified to shorten the antibody:antigen incubation time and tested in a field trial. Coupling the antibody to paper fibers at pH 7 increased the binding activity of the paper-antibody conjugate to allow incubation for 3 h at room temperature with no significant loss of competitive binding of progesterone. The relationship between progesterone concentrations measured by the modified and original enzyme immunoassays was r = .94 (n = 80 pairs). Milk samples (n = 67) collected 21 d after artificial insemination were classified by the original and modified methods as being from pregnant or nonpregnant cows using both spectrophotometric and visual evaluations. Comparison to subsequent rectal palpation or return to estrus showed that the two methods were comparable. A field trial was conducted involving 622 cows and 40 producers using the modified enzyme immunoassay method. The overall field trial accuracy of the enzyme immunoassay in diagnosing the cow's reproductive status for a single sample on d 21 after breeding was 71% for correct diagnosis of pregnancy and 81% for correct diagnosis of nonpregnancy. It was concluded that the modified method is a valuable technique for rapid monitoring of milk progesterone concentrations.