Vet Column 8-10-09
In 1982, two proteins specific to pregnancy were isolated. They were identified as pregnancy-specific protein A (PSPA) and pregnancy-specific protein B (PSPB). Further research determined that PSPB is produced by cells within the placenta; it is produced early in gestation; and it may persist in the bloodstream following calving for up to 90-100 days. Manufacturer recommendations indicate that pregnancy in cattle can be detected with this test for PSPB as early as 30 days post-breeding.
Due to the need to accurately detect non-pregnancy as soon as possible after breeding to improve reproductive management of the dairy herd, investigators from Cornell University recently published data comparing the usefulness of a blood test for PSPB with standard rectal palpation. Blood samples were taken via the tail vein, packaged, and sent by overnight courier to a commercial laboratory to determine PSPB concentrations using ELISA methodology (BioPRYN, BioTracking LLC, Moscow, Idaho). Results were electronically returned in four to five days with interpretations of pregnant, not pregnant, pregnant and retest recommended or not pregnant and retest recommended.
1,483 dairy cattle from 16 herds ranging in size from 30 head to 3,000 head in the central region of New York were used in this study. Phase I involved taking blood samples for comparison on the same day as rectal palpation was performed for determining pregnancy. Phase I was conducted between October 2006 and February 2007. The interval from last insemination to first rectal palpation varied among herds from approximately 35 to 60 days. Only cattle with accurate insemination dates were included in the study. Phase II involved only lactating cows from four of the 16 herds. In these four herds, use of prostaglandin and gonadatrophin releasing hormone were used to manage breeding.
The importance of the duration of PSPB in the blood following calving is reflected in the results of this study. Of the animals sampled, 9 percent were heifers, 36 percent were cows in their first lactation, and 55 percent of the cows were in their second or greater lactation. When disagreement between rectal palpation and the PSPB ELISA existed, 10.1 percent of the variation occurred when sampling was performed between 35 and 39 days post-insemination; 12.8 percent disagreement occurred between 40 and 44 days post-insemination; 8.5 percent disagreement occurred between 45 and 49 days post-insemination. When sampling occurred more than 50 days post-insemination, disagreement occurred only 2.7 percent of the time.
When rectal palpation determined pregnancy, the ELISA test agreed 95 percent of the time. When rectal palpation determined non-pregnancy, the ELISA test agreed 97 percent of the time.
Conclusions from this study indicate that good agreement existed between the two tests, particularly beyond 50 days post-insemination. Discrepant results appeared to be attributed to a nonviable fetus, embryonic loss, or fetal loss. An additional study using a different PSPB test in 1995 found that rectal palpation did not increase embryonic loss. As a result of this study, pregnancy test performance in dairy cattle using a PSPB ELISA test versus the standard rectal palpation pregnancy test is equal.