Enzyme linked immunosorbent assay for milk progesterone

A direct antigen heterologous enzyme linked immunosorbent assay (ELISA) for milk progesterone has been developed using progesterone-3-O-carboxymethyloxime-bovine serum albumin (P-3-O-CMO-BSA) antiserum and 17-α-hydroxy-progesterone-3-O-carboxymethyloxime-horseradish peroxidase (17-α-OH-P-3-O-CMO-HRP) enzyme conjugate. The data of the present study reveal that the homologous assay, which employed P-3-O-CMO-HRP as the label, showed no displacement. On the contrary, replacement of P-3-O-CMO-HRP with 17-α-OH-P-3-O-CMO-HRP as the label showed significant displacement and led to the development of a sensitive and specific assay. The recovery of the exogenously spiked progesterone from milk pools was in the range of 94.3-97.88% for toned milk and 97.6-101% for full-cream milk. The intra-assay and interassay coefficients of variation (CVs) ranged from 4.1-7.8% and 4.4-7.0%, respectively. A high ionic strength buffer was used to obtain released progesterone from binding protein/fat. The progesterone values measured in toned and full-cream milk ranged from 1.198-9.745 ng/mL and 6.949-14.923 ng/mL, respectively. The milk progesterone values obtained by this method correlated well with those obtained by radioimmunoassay; r = 0.95 (n = 65).