Rapid milk progesterone assay as a tool for the selection of potential donor cows prior to superovulation

This study investigated the accuracy of a commercially available rapid milk progesterone (P(4)) assay (RMPA) and its usefulness for the screening of potential donor cows prior to superovulatory treatment. Superovulation was induced in 90 lactating Holstein-Friesian crossbred dairy cows with twice daily injections over a 4-day period for a total of 40 mg follicle stimulating hormone (FSH-P), starting 9 to 13 d post estrus. Prior to induction of superovulation, a milk sample was collected and assayed for a P(4) level using the RMPA. The test determines P(4) by a simple visual color inspection of the respective sample, which is compared to a standard containing 10.5 ng/ml of P(4). All animals were divided into six groups according to the color intensity of their sample; three groups had a lower level, one group had an equal level and two groups had a higher P(4) level than the standard. Results of the semiquantitative RMPA were verified by a quantitative enzymeimmunoassay (EIA). Samples evaluated as equivalent to the standard had a mean P(4) level of 10.7 +/- 1.3 ng/ml (x +/- SEM). In total, P(4) levels differed (P<0.05) among groups, except in those with lower P(4) concentrations (1.1 +/- 0.0; 1.0 +/- 0.0; 3.7 +/- 1.5; 10.7 +/- 1.3; 13.8 +/- 1.3; 19.0 +/- 1.5 ng/ml, respectively). The correlation between RMPA-groups and EIA P(4) levels was 0.69 (P<0.001). Donors classified as having less P(4) than the standard yielded fewer corpora lutea (CL) (P<0.005), ova and embryos (P<0.05), and transferable embryos (P<0.05) compared with donors having similar or higher P(4) levels (3.4 +/- 1.0 vs 10.8 +/- 0.7 CL; 1.7 +/- 0.8 vs 6.2 +/- 0.9 ova and embryos; 1.2 +/- 0.7 vs 2.8 +/- 0.4 transferable embryos). Our results indicate that RMPA determines milk P(4) levels with sufficient accuracy and is a simple and useful tool for the screening of potential donor cows.