Is your prolaqctin purified or recombinant. You could do your own ELISA coating a plate with your prolactin trying to find the right concentration to coat the plate, then block the plate (bovine serum albumin) and then test your bovine plasma samples at different concentrations to see if you reach saturation. Use a negative and positive control always.
@Ricardo Espinola: Thank you for your advice on setting up an ELISA for bovine prolactin but my concern was to try to avoid to go through all the steps of an ELISA development and validation, which is fastidious, long and costly... That is why I would rather find a commercially available kit...
@Jelver Alexander Sierra restrepo: Thank you for the link to mybiosource. I did know this website but was a bit distrustful since the ELISA seems to me very very wide and unspecific. So I would be interested in knowing if you have had a personal experience with this provider and if it was positive...