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

Abstract

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.