Enzyme-linked immunosorbent assays of bovine lactoferrin and a 39-kilodalton protein found in mammary secretions during involution.

Enzyme-linked immunosorbent assays were developed for two proteins found in mammary secretions during the non-lactating period: lactoferrin and a 39-kdal protein. Minimum detectable concentrations were .12 ng/ml for lactoferrin and .0037 ng/ml for the 39-kdal protein. Standard curves were linear in the ranges of .4 to 100 ng/ml for lactoferrin and 2.4 to 30 ng/ml for the 39-kdal protein. The immunoassays were used to measure concentrations of the proteins in mammary secretions during involution. From the last day of milking to d 30 of involution, mean concentrations of lactoferrin and the 39-kdal protein increased from .82 +/- .35 to 78.5 +/- 12.43 mg/ml and from 11.8 +/- 3.8 to 84.4 +/- 21.1 micrograms/ml, respectively. The immunoassays described will be valuable for further studies on the synthesis and secretion of these proteins during mammary involution.